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Sample records for agb mass loss

  1. Starlight and Sandstorms: Mass Loss Mechanisms on the AGB

    NASA Astrophysics Data System (ADS)

    Höfner, S.

    2011-09-01

    There are strong observational indications that the dense slow winds of cool luminous AGB stars are driven by radiative pressure on dust grains which form in the extended atmospheres resulting from pulsation-induced shocks. For carbon stars, detailed models of outflows driven by amorphous carbon grains show good agreement with observations. Some still existing discrepancies may be due to a simplified treatment of cooling in shocks, drift of the grains relative to the gas, or effects of giant convection cells or dust-induced pattern formation. For stars with C/O < 1, recent models indicate that absorption by silicate dust is probably insufficient to drive their winds. A possible alternative is scattering by Fe-free silicate grains with radii of a few tenths of a micron. In this scenario one should expect less circumstellar reddening for M- and S-type AGB stars than for C-stars with comparable stellar parameters and mass loss rates.

  2. Constraining Mass Loss and Lifetimes of Low Mass, Low Metallicity AGB Stars

    NASA Astrophysics Data System (ADS)

    Rosenfield, P.; Marigo, P.; Girardi, L.; Dalcanton, J. J.; Bressan, A.; Gullieuszik, M.; Weisz, D. R.; Williams, B. F.; Dolphin, A.; Aringer, B.

    2015-08-01

    The evolution and lifetimes of thermally pulsing asymptotic giant branch (TP-AGB) stars suffer from significant uncertainties. We present a detailed framework for constraining model luminosity functions of TP-AGB stars using resolved stellar populations. We show an example of this method that compares various TP-AGB mass-loss prescriptions that differ in their treatments of mass loss before the onset of dust-driven winds (pre-dust). We find that models with more efficient pre-dust driven mass loss produce results consistent with observations, as opposed to more canonical mass-loss models. Efficient pre-dust driven mass-loss predicts, for [Fe/H] ≲ -1.2, that lower mass TP-AGB stars (M≲ 1 M⊙) must have lifetimes less than about 1.2 Myr.

  3. Probing the Mass Loss History of AGB Stars with Herschelfootnotemark

    NASA Astrophysics Data System (ADS)

    Kerschbaum, F.; Mecina, M.; Ottensamer, R.; Luntzer, A.; Groenewegen, M. A. T.; Blommaert, J. A. D. L.; Decin, L.; Royer, P.; Vandenbussche, B.; Waelkens, C.; Barlow, M.; Lim, T.

    2011-09-01

    An overview is given of AGB stars imaged with the PACS and SPIRE instruments on-board the Herschel Space Observatory in the framework of the MESS Guaranteed Time Key Programme. The objects AQ And, U Ant, W Aql, U Cam, RT Cap, Y CVn, TT Cyg, UX Dra, W Ori, AQ Sgr, and X TrA all show detached or extended circumstellar emission.

  4. Infrared photometry and evolution of mass-losing AGB stars. III. Mass loss rates of MS and S stars

    NASA Astrophysics Data System (ADS)

    Guandalini, R.

    2010-04-01

    Context. The asymptotic giant branch (AGB) phase marks the end of the evolution for low- and intermediate-mass stars, which are fundamental contributors to the mass return to the interstellar medium and to the chemical evolution of galaxies. The detailed understanding of mass loss processes is hampered by the poor knowledge of the luminosities and distances of AGB stars. Aims: In a series of papers we are trying to establish criteria permitting a more quantitative determination of luminosities for the various types of AGB stars, using the infrared (IR) fluxes as a basis. An updated compilation of the mass loss rates is also required, as it is crucial in our studies of the evolutionary properties of these stars. In this paper we concentrate our analysis on the study of the mass loss rates for a sample of galactic S stars. Methods: We reanalyze the properties of the stellar winds for a sample of galactic MS, S, SC stars with reliable estimates of the distance on the basis of criteria previously determined. We then compare the resulting mass loss rates with those previously obtained for a sample of C-rich AGB stars. Results: Stellar winds in S stars are on average less efficient than those of C-rich AGB stars of the same luminosity. Near-to-mid infrared colors appear to be crucial in our analysis. They show a good correlation with mass loss rates in particular for the Mira stars. We suggest that the relations between the rates of the stellar winds and both the near-to-mid infrared colors and the periods of variability improve the understanding of the late evolutionary stages of low mass stars and could be the origin of the relation between the rates of the stellar winds and the bolometric magnitudes.

  5. Luminosities and mass-loss rates of SMC and LMC AGB stars and red supergiants

    NASA Astrophysics Data System (ADS)

    Groenewegen, M. A. T.; Sloan, G. C.; Soszyński, I.; Petersen, E. A.

    2009-11-01

    Context: Mass loss is one of the fundamental properties of Asymptotic Giant Branch (AGB) stars, and through the enrichment of the interstellar medium, AGB stars are key players in the life cycle of dust and gas in the universe. However, a quantitative understanding of the mass-loss process is still largely lacking, particularly its dependence on metallicity. Aims: To investigate the relation between mass loss, luminosity and pulsation period for a large sample of evolved stars in the Small and Large Magellanic Cloud. Methods: Dust radiative transfer models are presented for 101 carbon stars and 86 oxygen-rich evolved stars in the Magellanic Clouds for which 5-35 μm Spitzer IRS spectra are available. The spectra are complemented with available optical and infrared photometry to construct the spectral energy distribution. A minimisation procedure is used to fit luminosity, mass-loss rate and dust temperature at the inner radius. Different effective temperatures and dust content are also considered. Periods from the literature and from new OGLE-III data are compiled and derived. Results: We derive (dust) mass-loss rates and luminosities for the entire sample. Based on luminosities, periods and amplitudes and colours, the O-rich stars are classified as foreground objects, AGB stars and Red Super Giants. For the O-rich stars silicates based on laboratory optical constants are compared to “astronomical silicates”. Overall, the grain type by Volk & Kwok (1988, ApJ, 331, 435) fits the data best. However, the fit based on laboratory optical constants for the grains can be improved by abandoning the small-particle limit. The influence of grain size, core-mantle grains and porosity are explored. A computationally convenient method that seems to describe the observed properties in the 10 μm window are a distribution of hollow spheres with a large vacuum fraction (typically 70%), and grain size of about 1 μm. Relations between mass-loss rates and luminosity and pulsation

  6. Evolution of thermally pulsing asymptotic giant branch stars. IV. Constraining mass loss and lifetimes of low mass, low metallicity AGB stars

    SciTech Connect

    Rosenfield, Philip; Dalcanton, Julianne J.; Weisz, Daniel; Williams, Benjamin F.; Marigo, Paola; Girardi, Léo; Gullieuszik, Marco; Bressan, Alessandro; Dolphin, Andrew; Aringer, Bernhard

    2014-07-20

    The evolution and lifetimes of thermally pulsating asymptotic giant branch (TP-AGB) stars suffer from significant uncertainties. In this work, we analyze the numbers and luminosity functions of TP-AGB stars in six quiescent, low metallicity ([Fe/H] ≲ –0.86) galaxies taken from the ACS Nearby Galaxy Survey Treasury sample, using Hubble Space Telescope (HST) photometry in both optical and near-infrared filters. The galaxies contain over 1000 TP-AGB stars (at least 60 per field). We compare the observed TP-AGB luminosity functions and relative numbers of TP-AGB and red giant branch (RGB) stars, N{sub TP-AGB}/N{sub RGB}, to models generated from different suites of TP-AGB evolutionary tracks after adopting star formation histories derived from the HST deep optical observations. We test various mass-loss prescriptions that differ in their treatments of mass loss before the onset of dust-driven winds (pre-dust). These comparisons confirm that pre-dust mass loss is important, since models that neglect pre-dust mass loss fail to explain the observed N{sub TP-AGB}/N{sub RGB} ratio or the luminosity functions. In contrast, models with more efficient pre-dust mass loss produce results consistent with observations. We find that for [Fe/H] ≲ –0.86, lower mass TP-AGB stars (M ≲ 1 M{sub ☉}) must have lifetimes of ∼0.5 Myr and higher masses (M ≲ 3 M{sub ☉}) must have lifetimes ≲ 1.2 Myr. In addition, assuming our best-fitting mass-loss prescription, we show that the third dredge-up has no significant effect on TP-AGB lifetimes in this mass and metallicity range.

  7. The mass-loss evolution of oxygen-rich AGB stars and its consequences for stellar evolution

    NASA Astrophysics Data System (ADS)

    van der Veen, W. E. C. J.

    1989-02-01

    A semiempirical mass loss equation (MLE) for Asymptotic Giant Branch (AGB) stars with oxygen-rich circumstellar shells is presented. The MLE is a function of stellar luminosity, expansion velocity of the circumstellar shell, and the ratio between the IRAS 25 and 12 micron flux densities. The results are compared with previously derived MLEs. The IRAS Point Source Catalog is used to find the mass loss as a function of time. The MLE is tested by estimating the total mass lost on the AGB. A simple expression is found relating the initial main sequence mass and the maximum AGB luminosity. The time-dependent properties of the MLE are tested using a sample of Miras and OH/IR stars. A relation between period, luminosity, and stellar envelope mass is found and compared with the observed period-luminosity relations for globular cluster Miras and Miras in the LMC. Good agreement is found.

  8. Evolution of Thermally Pulsing Asymptotic Giant Branch Stars. V. Constraining the Mass Loss and Lifetimes of Intermediate-mass, Low-metallicity AGB Stars

    NASA Astrophysics Data System (ADS)

    Rosenfield, Philip; Marigo, Paola; Girardi, Léo; Dalcanton, Julianne J.; Bressan, Alessandro; Williams, Benjamin F.; Dolphin, Andrew

    2016-05-01

    Thermally pulsing asymptotic giant branch (TP-AGB) stars are relatively short lived (less than a few Myr), yet their cool effective temperatures, high luminosities, efficient mass loss, and dust production can dramatically affect the chemical enrichment histories and the spectral energy distributions of their host galaxies. The ability to accurately model TP-AGB stars is critical to the interpretation of the integrated light of distant galaxies, especially in redder wavelengths. We continue previous efforts to constrain the evolution and lifetimes of TP-AGB stars by modeling their underlying stellar populations. Using Hubble Space Telescope (HST) optical and near-infrared photometry taken of 12 fields of 10 nearby galaxies imaged via the Advanced Camera for Surveys Nearby Galaxy Survey Treasury and the near-infrared HST/SNAP follow-up campaign, we compare the model and observed TP-AGB luminosity functions as well as the ratio of TP-AGB to red giant branch stars. We confirm the best-fitting mass-loss prescription, introduced by Rosenfield et al., in which two different wind regimes are active during the TP-AGB, significantly improves models of many galaxies that show evidence of recent star formation. This study extends previous efforts to constrain TP-AGB lifetimes to metallicities ranging ‑1.59 ≲ {{[Fe/H]}} ≲ ‑0.56 and initial TP-AGB masses up to ˜4 M ⊙, which include TP-AGB stars that undergo hot-bottom burning. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

  9. Evolution of Thermally Pulsing Asymptotic Giant Branch Stars. V. Constraining the Mass Loss and Lifetimes of Intermediate-mass, Low-metallicity AGB Stars

    NASA Astrophysics Data System (ADS)

    Rosenfield, Philip; Marigo, Paola; Girardi, Léo; Dalcanton, Julianne J.; Bressan, Alessandro; Williams, Benjamin F.; Dolphin, Andrew

    2016-05-01

    Thermally pulsing asymptotic giant branch (TP-AGB) stars are relatively short lived (less than a few Myr), yet their cool effective temperatures, high luminosities, efficient mass loss, and dust production can dramatically affect the chemical enrichment histories and the spectral energy distributions of their host galaxies. The ability to accurately model TP-AGB stars is critical to the interpretation of the integrated light of distant galaxies, especially in redder wavelengths. We continue previous efforts to constrain the evolution and lifetimes of TP-AGB stars by modeling their underlying stellar populations. Using Hubble Space Telescope (HST) optical and near-infrared photometry taken of 12 fields of 10 nearby galaxies imaged via the Advanced Camera for Surveys Nearby Galaxy Survey Treasury and the near-infrared HST/SNAP follow-up campaign, we compare the model and observed TP-AGB luminosity functions as well as the ratio of TP-AGB to red giant branch stars. We confirm the best-fitting mass-loss prescription, introduced by Rosenfield et al., in which two different wind regimes are active during the TP-AGB, significantly improves models of many galaxies that show evidence of recent star formation. This study extends previous efforts to constrain TP-AGB lifetimes to metallicities ranging ‑1.59 ≲ {{[Fe/H]}} ≲ ‑0.56 and initial TP-AGB masses up to ∼4 M ⊙, which include TP-AGB stars that undergo hot-bottom burning. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

  10. Pulsation-triggered Mass Loss from AGB Stars: The 60 Day Critical Period

    NASA Astrophysics Data System (ADS)

    McDonald, I.; Zijlstra, A. A.

    2016-06-01

    Low- and intermediate-mass stars eject much of their mass during the late, red giant branch (RGB) phase of evolution. The physics of their strong stellar winds is still poorly understood. In the standard model, stellar pulsations extend the atmosphere, allowing a wind to be driven through radiation pressure on condensing dust particles. Here, we investigate the onset of the wind, using nearby RGB stars drawn from the Hipparcos catalog. We find a sharp onset of dust production when the star first reaches a pulsation period of 60 days. This approximately coincides with the point where the star transitions to the first overtone pulsation mode. Models of the spectral energy distributions show stellar mass-loss rate suddenly increasing at this point, by a factor of ∼10 over the existing (chromospherically driven) wind. The dust emission is strongly correlated with both pulsation period and amplitude, indicating stellar pulsation is the main trigger for the strong mass loss, and determines the mass-loss rate. Dust emission does not strongly correlate with stellar luminosity, indicating radiation pressure on dust has little effect on the mass-loss rate. RGB stars do not normally appear to produce dust, whereas dust production by asymptotic giant branch stars appears commonplace, and is probably ubiquitous above the RGB-tip luminosity. We conclude that the strong wind begins with a step change in mass-loss rate and is triggered by stellar pulsations. A second rapid mass-loss-rate enhancement is suggested when the star transitions to the fundamental pulsation mode at a period of ∼300 days.

  11. Pulsation-triggered Mass Loss from AGB Stars: The 60 Day Critical Period

    NASA Astrophysics Data System (ADS)

    McDonald, I.; Zijlstra, A. A.

    2016-06-01

    Low- and intermediate-mass stars eject much of their mass during the late, red giant branch (RGB) phase of evolution. The physics of their strong stellar winds is still poorly understood. In the standard model, stellar pulsations extend the atmosphere, allowing a wind to be driven through radiation pressure on condensing dust particles. Here, we investigate the onset of the wind, using nearby RGB stars drawn from the Hipparcos catalog. We find a sharp onset of dust production when the star first reaches a pulsation period of 60 days. This approximately coincides with the point where the star transitions to the first overtone pulsation mode. Models of the spectral energy distributions show stellar mass-loss rate suddenly increasing at this point, by a factor of ˜10 over the existing (chromospherically driven) wind. The dust emission is strongly correlated with both pulsation period and amplitude, indicating stellar pulsation is the main trigger for the strong mass loss, and determines the mass-loss rate. Dust emission does not strongly correlate with stellar luminosity, indicating radiation pressure on dust has little effect on the mass-loss rate. RGB stars do not normally appear to produce dust, whereas dust production by asymptotic giant branch stars appears commonplace, and is probably ubiquitous above the RGB-tip luminosity. We conclude that the strong wind begins with a step change in mass-loss rate and is triggered by stellar pulsations. A second rapid mass-loss-rate enhancement is suggested when the star transitions to the fundamental pulsation mode at a period of ˜300 days.

  12. Stellar Dust Production in Chemically Primitive Environments: Infrared Lightcurves and Mass Loss in Extremely Metal-poor AGB Stars

    NASA Astrophysics Data System (ADS)

    Sonneborn, George

    In their final stage of evolution, asymptotic giant branch (AGB) stars inject a substantial amount of dust into the surrounding interstellar medium, potentially dominating the total stellar dust budgets of their host galaxies. However, stellar models conflict over whether metal-poor AGB stars can condense enough dust to drive a strong stellar wind, so it is unclear what role AGB stars play in the early Universe compared to other dust sources, e.g., in high-redshift quasars that show evidence for massive dust reservoirs. Empirically, AGB stars that are massive enough to contribute in the early Universe are only well studied in the Milky Way and the nearby Magellanic Clouds; all three environments are relatively metal-rich and thus unlikely to be representative of high-redshift AGB stars. This lack of observations of metal-poor AGB stars motivated the survey of DUST in Nearby Galaxies with Spitzer (DUSTiNGS), which imaged 50 nearby dwarf galaxies in the infrared and identified 526 dusty "extreme" AGB stars. The DUSTiNGS stars confirm that dust can form at metallicities as low as 0.008 solar, more than an order of magnitude lower than had been previously observed. However, very little is known about the DUSTiNGS stars; among the unknowns are the photospheric chemistries, stellar masses, temperatures, luminosities, pulsation periods and amplitudes, dust-production rates, and even their statuses as bona fide AGB stars. To eliminate these unknowns, we were awarded 56 hours of Priority 1 observing time in Spitzer's cycle 11 to obtain 6 new epochs of imaging for a subset of the DUSTiNGS variables over an 18 month baseline. These will be the first infrared light curves of metal-poor, dust-producing AGB stars, allowing us to study the influence of metallicity on pulsation and dust production. Combined with additional archival data, our cycle-11 Spitzer program will allow estimates of all of the parameters listed above, enabling the first direct comparisons to models of AGB

  13. Nucleosynthesis in Low Mass Very Metal Poor AGB Stars

    NASA Astrophysics Data System (ADS)

    Serenelli, A.

    The evolution of a 1.5 M⊙, Z= 10-5 stellar model has been followed starting at the ZAMS up to the thermally pulsating asymptotic giant branch (TP-AGB) phase. Calculations were done using the LPCODE [1], to which some changes were done. The most important and relevant to this work is the incorporation of a full nuclear network from H to Po, comprising about 525 isotopes and 910 nuclear reactions, appropriate for the computation of the s-process occurring in AGB stars. Convection is treated according to the mixing length theory (λMLT = 1.7) and convective mixing as a diffusive process. Diffusive overshooting is also included according to [2] and the free parameter f adopted is 0.015. Mass loss is given by the Reimers formula, with the parameter η = 1.

  14. Probing the mass-loss history of AGB and red supergiant stars from CO rotational line profiles. II. CO line survey of evolved stars: derivation of mass-loss rate formulae

    NASA Astrophysics Data System (ADS)

    De Beck, E.; Decin, L.; de Koter, A.; Justtanont, K.; Verhoelst, T.; Kemper, F.; Menten, K. M.

    2010-11-01

    Context. The evolution of intermediate and low-mass stars on the asymptotic giant branch is dominated by their strong dust-driven winds. More massive stars evolve into red supergiants with a similar envelope structure and strong wind. These stellar winds are a prime source for the chemical enrichment of the interstellar medium. Aims: We aim to (1) set up simple and general analytical expressions to estimate mass-loss rates of evolved stars, and (2) from those calculate estimates for the mass-loss rates of the asymptotic giant branch, red supergiant, and yellow hypergiant stars in our galactic sample. Methods: The rotationally excited lines of carbon monoxide (CO) are a classic and very robust diagnostic in the study of circumstellar envelopes. When sampling different layers of the circumstellar envelope, observations of these molecular lines lead to detailed profiles of kinetic temperature, expansion velocity, and density. A state-of-the-art, nonlocal thermal equilibrium, and co-moving frame radiative transfer code that predicts CO line intensities in the circumstellar envelopes of late-type stars is used in deriving relations between stellar and molecular-line parameters, on the one hand, and mass-loss rate, on the other. These expressions are applied to our extensive CO data set to estimate the mass-loss rates of 47 sample stars. Results: We present analytical expressions for estimating the mass-loss rates of evolved stellar objects for 8 rotational transitions of the CO molecule and thencompare our results to those of previous studies. Our expressions account for line saturation and resolving of the envelope, thereby allowing accurate determination of very high mass-loss rates. We argue that, for estimates based on a single rotational line, the CO(2-1) transition provides the most reliable mass-loss rate. The mass-loss rates calculated for the asympotic giant branch stars range from 4 × 10-8 M⊙ yr-1 up to 8 × 10-5 M⊙ yr-1. For red supergiants they reach

  15. Mass loss

    NASA Technical Reports Server (NTRS)

    Goldberg, Leo

    1987-01-01

    Observational evidence for mass loss from cool stars is reviewed. Spectra line profiles are used for the derivation of mass-loss rates with the aid of the equation of continuity. This equation implies steady mass loss with spherical symmetry. Data from binary stars, Mira variables, and red giants in globular clusters are examined. Silicate emission is discussed as a useful indicator of mass loss in the middle infrared spectra. The use of thermal millimeter-wave radiation, Very Large Array (VLA) measurement of radio emission, and OH/IR masers are discussed as a tool for mass loss measurement. Evidence for nonsteady mass loss is also reviewed.

  16. Dusty Mass Loss from Galactic Asymptotic Giant Branch Stars

    NASA Astrophysics Data System (ADS)

    Sargent, Benjamin A.; Srinivasan, Sundar; Meixner, Margaret; Kastner, Joel H.

    2016-06-01

    We are probing how mass loss from Asymptotic Giant Branch (AGB) stars depends upon their metallicity. Asymptotic giant branch (AGB) stars are evolved stars that eject large parts of their mass in outflows of dust and gas in the final stages of their lives. Our previous studies focused on mass loss from AGB stars in lower metallicity galaxies: the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC). In our present study, we analyze AGB star mass loss in the Galaxy, with special attention to the Bulge, to investigate how mass loss differs in an overall higher metallicity environment. We construct radiative transfer models of the spectral energy distributions (SEDs) of stars in the Galaxy identified as AGB stars from infrared and optical surveys. Our Magellanic Cloud studies found that the AGB stars with the highest mass loss rates tended to have outflows with carbon-rich dust, and that overall more carbon-rich (C-rich) dust than oxygen-rich (O-rich) was produced by AGB stars in both LMC and SMC. Our radiative transfer models have enabled us to determine reliably the dust chemistry of the AGB star from the best-fit model. For our Galactic sample, we are investigating both the dust chemistries of the AGB stars and their mass-loss rates, to compare the balance of C-rich dust to O-rich dust between the Galactic bulge and the Magellanic Clouds. We are also constructing detailed dust opacity models of AGB stars in the Galaxy for which we have infrared spectra; e.g., from the Spitzer Space Telescope Infrared Spectrograph (IRS). This detailed dust modeling of spectra informs our choice of dust properties to use in radiative transfer modeling of SEDs of Galactic AGB stars. BAS acknowledges funding from NASA ADAP grant NNX15AF15G.

  17. Mass Loss from Low- and Intermediate-mass Stars

    NASA Astrophysics Data System (ADS)

    Wood, P. R.

    2007-11-01

    Low- and intermediate-mass single stars (LIMS) have initial masses M<~6-7 Msolar. They end up as white dwarfs of ~0.6-1.4 Msolar, the rest of their mass being lost during their nuclear-burning lifetimes. Stellar pulsation theory can be used to estimate current (as opposed to initial) stellar masses and can be used to trace accumulated mass loss when the initial mass is known. Some examples are given for RR Lyrae stars, first giant branch (FGB) and asymptotic giant branch (AGB) stars, and Cepheid variables. Most of the mass loss from LIMS is thought to occur on the FGB and AGB, although it has been argued that pulsation masses derived for Cepheids suggest that there is significant mass loss in earlier evolutionary phases. Direct estimates of mass loss rates can also be used to estimate the amounts of mass lost from LIMS. Some recent Spitzer-based estimates of mass loss rates for AGB stars in the Magellanic Clouds are discussed. Finally, binary and variable AGB stars that may be related to asymmetic mass loss such as that seen in elliptical and bipolar planetary nebulae are discussed.

  18. Mass Loss from Betelgeuse

    NASA Astrophysics Data System (ADS)

    Richards, A. M. S.

    2013-05-01

    Betelgeuse is just starting to produce a wind which is thick enough to form dust. However, the grains seem to coalesce at much greater distances than those in "dust-driven" winds from later-stage AGB and RSG stars. Is the mass loss mechanism different, and how will it evolve? We know a great deal about the kinematics of the more evolved winds, thanks to sub-au imaging using masers, and easily-resolved CO shells, but Betelgeuse is a much fainter target, only resolved with great difficulty (although ALMA will change that). On the other hand, Betelgeuse was the first star other than the Sun to be imaged in detail in the radio as well as optical. Radio studies from the photosphere to the astropause will reveal: How is mass lost from the stellar surface? In what form is this returned to the ISM? These results could even help to answer: How will Betelgeuse evolve in the next few millennia?

  19. Dust Production and Mass Loss in Cool Evolved Stars

    NASA Technical Reports Server (NTRS)

    Boyer, M. L.

    2013-01-01

    Following the red giant branch phase and the subsequent core He-burning phase, the low- to intermediate-mass stars (0.8mass <8) begin to ascend the asymptotic giant branch (AGB). Pulsations levitate material from the stellar surface and provide density enhancements and shocks, which can encourage dust formation and re-processing. The dust composition depends on the atmospheric chemistry (abundance of carbon relative to oxygen), which is altered by dredging up newly formed carbon to the surface of the star. I will briefly review the current status of models that include AGB mass loss and relate them to recent observations of AGB stars from the Surveying the Agents of Galaxy Evolution (SAGE) Spitzer surveys of the Small and Large Magellanic Clouds, including measures of the total dust input to the interstellar medium from AGB stars.

  20. Hiding in plain sight - red supergiant imposters? Super-AGB stars - bridging the divide between low/intermediate-mass and high-mass stars

    NASA Astrophysics Data System (ADS)

    Doherty, Carolyn Louise; Gil-Pons, Pilar; Lattanzio, John; Siess, Lionel

    2015-08-01

    Super Asymptotic Giant Branch (Super-AGB) stars reside in the mass range ~ 6.5-10 M⊙ and bridge the divide between low/intermediate-mass and massive stars. They are characterised by off-centre carbon ignition prior to a thermally pulsing phase which can consist of many tens to even thousands of thermal pulses. With their high luminosities and very large, cool, red stellar envelopes, these stars appear seemingly identical to their slightly more massive red supergiant counterparts. Due to their similarities, super-AGB stars may therefore act as stellar imposters and contaminate red supergiant surveys. Super-AGB stars undergo relatively extreme nucleosynthetic conditions, with very efficient proton-capture nucleosynthesis occurring at the base of the convective envelope and also heavy element (s-process) production during the thermal pulse to be later mixed to the surface during third dredge-up events. The surface enrichment from these two processes may result in a clear nucleosynthetic signature to differentiate these two classes of star.The final fate of super-AGB stars is also quite uncertain and depends primarily on the competition between the core growth and mass-loss rates. If the stellar envelope is removed prior to the core reaching the Chandrasekhar mass, an O-Ne white dwarf will remain, otherwise the star will undergo an electron-capture supernova leaving behind a neutron star. We describe the factors which influence these different final fate channels, such as the efficiency of convection, the mass-loss rates, the third dredge-up efficiency and the Fe-peak opacity instability which may lead to expulsion of the entire remaining stellar envelope. We determine the relative fraction of super-AGB stars that end life as either an O-Ne white dwarf or as a neutron star, and provide a mass limit for the lowest mass supernova over a broad range of metallicities from the earliest time (Z=0) right through until today (Z~0.04).

  1. Carbon dust particle size distributions around mass-losing AGB stars

    NASA Astrophysics Data System (ADS)

    Jura, M.

    1997-03-01

    Solids of presolar SiC and interstellar carbon have qualitatively similar relative size distribution for particles with radii, a, in the range 0.35 μmAGB stars such as the well studied IRC+10216 seem to be smaller than the interstellar or presolar particles. The close binary system, the Red Rectangle, appears to produce much larger grains than does IRC+10216, and we suggest that many of the interstellar and presolar particles with radii >0.35 μm are produced by interacting binary systems rather than single mass-losing stars.

  2. Nucleosynthesis Predictions for Intermediate-Mass AGB Stars: Comparison to Observations of Type I Planetary Nebulae

    NASA Technical Reports Server (NTRS)

    Karakas, Amanda I.; vanRaai, Mark A.; Lugaro, Maria; Sterling, Nicholas C.; Dinerstein, Harriet L.

    2008-01-01

    Type I planetary nebulae (PNe) have high He/H and N/O ratios and are thought to be descendants of stars with initial masses of approx. 3-8 Stellar Mass. These characteristics indicate that the progenitor stars experienced proton-capture nucleosynthesis at the base of the convective envelope, in addition to the slow neutron capture process operating in the He-shell (the s-process). We compare the predicted abundances of elements up to Sr from models of intermediate-mass asymptotic giant branch (AGB) stars to measured abundances in Type I PNe. In particular, we compare predictions and observations for the light trans-iron elements Se and Kr, in order to constrain convective mixing and the s-process in these stars. A partial mixing zone is included in selected models to explore the effect of a C-13 pocket on the s-process yields. The solar-metallicity models produce enrichments of [(Se, Kr)/Fe] less than or approx. 0.6, consistent with Galactic Type I PNe where the observed enhancements are typically less than or approx. 0.3 dex, while lower metallicity models predict larger enrichments of C, N, Se, and Kr. O destruction occurs in the most massive models but it is not efficient enough to account for the greater than or approx. 0.3 dex O depletions observed in some Type I PNe. It is not possible to reach firm conclusions regarding the neutron source operating in massive AGB stars from Se and Kr abundances in Type I PNe; abundances for more s-process elements may help to distinguish between the two neutron sources. We predict that only the most massive (M grester than or approx.5 Stellar Mass) models would evolve into Type I PNe, indicating that extra-mixing processes are active in lower-mass stars (3-4 Stellar Mass), if these stars are to evolve into Type I PNe.

  3. The effects of rotation on the surface composition and yields of low mass AGB stars.

    NASA Astrophysics Data System (ADS)

    Cristallo, S.; Piersanti, L.; Straniero, O.

    Over the past 20 years, stellar evolutionary models have been strongly improved in order to reproduce with reasonable accuracy both photometric and spectroscopic observations. Notwithstanding, the majority of these models do not take into account macroscopic phenomena, like rotation and/or magnetic fields. Their explicit treatment could modify stellar physical and chemical properties. One of the most interesting problems related to stellar nucleosynthesis is the behavior of the s-process spectroscopic indexes ([hs/ls] and [Pb/hs]) in Asymptotic Giant Branch (AGB) stars. In this contribution we show that, for a fixed metallicity, rotation can lead to a spread in the [hs/ls] and [Pb/hs] in low-mass AGB stars. In particular, we demonstrate that the Eddington-Sweet and the Goldreich-Schubert-Fricke instabilities may have enough time to smear the 13C-pocket (the major neutron source) and the 14N-pocket (the major neutron poison). In fact, a different overlap between these pockets leads to a different neutrons-to-seeds ratio, with important consequences on the corresponding s-process distributions. Possible consequences on the chemical evolution of Galactic globular clusters are discussed.

  4. Approaching a Physical Calibration of the AGB Phase

    NASA Astrophysics Data System (ADS)

    Marigo, Paola

    2015-08-01

    The widespread impact of Asymptotic Giant Branch (AGB) stars on the observed properties of galaxies is universally accepted. Despite their importance, severe uncertainties plague AGB models and propagate through to current population synthesis studies of galaxies, undermining the interpretation of a galaxy's basic properties (mass, age, chemical evolution, dust budget). The only reliable path forward is to apply a physically-sound calibration of AGB stellar models in which all main physical processes and their interplay are taken into account (e.g., mixing, mass loss, nucleosynthesis, pulsation, molecular chemistry, dust formation). In this context, I will review recent and ongoing efforts to calibrate the evolution of AGB stars, which combine an all-round theoretical approach anchored by stellar physics with exceptionally high quality data of resolved AGB stars in the Milky Way and nearby galaxies.

  5. Characterizing uncertainties of the national-scale forest gross aboveground biomass (AGB) loss estimate: a case study of the Democratic Republic of the Congo

    NASA Astrophysics Data System (ADS)

    Tyukavina, A.; Stehman, S.; Potapov, P.; Turubanova, S.; Baccini, A.; Goetz, S. J.; Laporte, N. T.; Houghton, R. A.; Hansen, M.

    2013-12-01

    Modern remote sensing techniques enable the mapping and monitoring of aboveground biomass (AGB) carbon stocks without relying on extensive in situ measurements. The Democratic Republic of the Congo (DRC) is among the countries where a national forest inventory (NFI) has yet to be established due to a lack of infrastructure and political instability. We demonstrate a method for producing national-scale gross AGB loss estimates and quantifying uncertainty of the estimates using remotely sensed-derived forest cover loss and biomass carbon density data. Forest cover type and loss were characterized using published Landsat-based data sets and related to LIDAR-derived biomass data from the Geoscience Laser Altimeter System (GLAS). We produced two gross AGB loss estimates for the DRC for the last decade (2000-2010): a conservative estimate accounting for classification errors in the 60-m resolution FACET forest cover change product, and a maximal estimate that also took into consideration omitted change at the 30m spatial resolution. Omitted disturbances were largely related to smallholder agriculture, the detection of which is scale-dependent. The use of LIDAR data as a substitute for NFI data to estimate AGB loss based on Landsat-derived activity data was demonstrated. Comparisons of our forest cover loss and AGB estimates with published studies raise the issue of scale in forest cover change mapping and its impact on carbon stock change estimation using remotely sensed data.

  6. Rotation and Mass Loss

    NASA Astrophysics Data System (ADS)

    Owocki, S.

    2008-06-01

    Stellar rotation can play an important role in structuring and enhancing the mass loss from massive stars. Initial 1D models focussed on the expected centrifugal enhancement of the line-driven mass flux from the equator of a rotating star, but the review here emphasizes that the loss of centrifugal support away from the stellar surface actually limits the steady mass flux to just the point-star CAK value, with models near critical rotation characterized by a slow, subcritical acceleration. Recent suggestions that such slow outflows might have high enough density to explain disks in Be or B[e] stars are examined in the context of 2D simulations of the ``Wind Compressed Disk'' (WCD) paradigm, together with a review of the tendency for poleward components of the line-driving force to inhibit WCD formation. When one accounts for equatorial gravity darkening, the net tendency is in fact for the relatively bright regions at higher latitude to drive a faster, denser ``bipolar'' outflow. I discuss the potential relevance for the bipolar form of nebulae from LBV stars like η Carinae, but emphasize that, since the large mass loss associated with the eruption of eta Carinae's Homunculus would heavily saturate line-driving, explaining its bipolar form requires development of analogous models for continuum-driven mass loss. I conclude with a discussion of how radiation seems inherently ill-suited to supporting or driving a geometrically thin, but optically thick disk or disk outflow. The disks inferred in Be and B[e] stars may instead be centrifugally ejected, with radiation inducing an ablation flow from the disk surface, and thus perhaps playing a greater role in destroying (rather than creating) an orbiting, circumstellar disk.

  7. S-process nucleosynthesis in AGB stars with the full spectrum of turbulence scheme for convection.

    NASA Astrophysics Data System (ADS)

    Yagüe, A.; García-Hernández, D. A.; Ventura, P.; Lugaro, M.

    2016-07-01

    The chemical evolution of asymptotic giant branch (AGB) stars models depends greatly on the input physics (e.g. convective model, mass loss recipe). Variations of hot bottom burning (HBB) strength, or third dredge-up (TDU) efficiency are among the main consequences of adopting different input physics in the AGB models. The ATON evolutionary code stands apart from others in that it uses the Full Spectrum of Turbulence convective model. Here we present the first results of a newly developed s-process nucleosynthesis module for ATON AGB models. Our results are compared also with observations and theoretical predictions of present AGB nucleosynthesis models using different input physics.

  8. CEN 34 - high-mass YSO in M 17 or background post-AGB star?

    NASA Astrophysics Data System (ADS)

    Chen, Zhiwei; Nürnberger, Dieter E. A.; Chini, Rolf; Liu, Yao; Fang, Min; Jiang, Zhibo

    2013-09-01

    We investigate the proposed high-mass young stellar object (YSO) candidate CEN 34, thought to be associated with the star-forming region M 17. Its optical to near-infrared (550-2500 nm) spectrum reveals several photospheric absorption features, such as Hα, the Ca ii triplet, and the CO bandhead, but lacks emission lines. The spectral features in the range 8375-8770 Å are used to constrain an effective temperature Teff = 5250 ± 250 K (early-/mid-G) and a log g = 2.0 ± 0.3 (supergiant). The spectral energy distribution (SED) displays a faint infrared excess that resembles that of a high-mass YSO or an evolved star of intermediate mass. Moreover, the observed temperature and surface gravity are identical for high-mass YSOs and evolved stars. The radial velocity of CEN 34 relative to the local standard of rest (VLSR) as obtained from various photospheric lines is of the order of -60 km s-1 and thus distinct from the +25 km s-1 found for several OB stars in the cluster and for the associated molecular cloud. The SED modeling yields 10-4 M⊙ of circumstellar material, which contributes only a tiny fraction to the total visual extinction (11 mag). The distance of CEN 34 is between 2.0 kpc and 4.5 kpc. In the case of a YSO, a dynamical ejection process is proposed to explain the VLSR difference between CEN 34 and M 17. Additionally, to match the temperature and luminosity, we speculate that CEN 34 had accumulated the bulk of its mass with an accretion rate >4 × 10-3M⊙/yr over a very short time span (~103 yrs), and it is currently undergoing a phase of gravitational contraction without any further mass gain. However, all the aforementioned characteristics of CEN 34 are compatible with an evolved star of 5-7 M⊙ and an age of 50-100 Myr, so it is most likely a background post-AGB star with a distance between 2.0 kpc and 4.5 kpc. We consider the latter classification as the more likely interpretation. Further discrimination of the two possible scenarios should come

  9. 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.

  10. Radial density profiles of PNe halos from numerical models of mass-loss history

    NASA Astrophysics Data System (ADS)

    Verbena, Juan-Luis; Schröder, Klaus-Peter; Wachter, Astrid

    2012-08-01

    We review the stellar mass loss of red giants and tip-AGB objects analizing the variation in the outflow velocity for different mass models (Wachter et al. 2002). We approach the superwind problem and see the evolution of tip-AGB stars via previously made mass-loss histories that are consistent with the Weidemann initial-final mass relationship (for carbon-rich stars). Finally density profiles are produced from these mass-loss histories, and the corresponding line-of-sight integration is compared with observational data (Phillips et al. 2009). We note the resemblance between the results obtained with our models and the observational data. We are thus able to reproduce the general trends of the emission from simple models (see Verbena et al. 2011).

  11. Yields from low metallicity, intermediate mass AGB stars:. Their role for the CNO and lithium abundances in Globular Cluster stars

    NASA Astrophysics Data System (ADS)

    Ventura, P.; D'Antona, F.; Mazzitelli, I.

    2002-10-01

    We present the results of extensive computation of the Thermal Pulse phase AGB evolution of stars of metallicities in mass fraction 2 x 10-4 <= Z <= 0.01, for those masses in the range 2.5 <= M/Msun <= 6, which suffer the Hot Bottom Burning (HBB) phase. The evolution is fully computed, by assuming a mass loss rate consistent with the observations of the Magellanic Clouds lithium-rich stars, and modelling convection with the Full Spectrum of Turbulence model by Canuto and Mazzitelli. The results are discussed in the framework of their importance for the evolution of proto-Globular Clusters, whose spectra show that the stars are very probably formed from matter contaminated by the ejecta of these stars, or have accreted it after formation. The main results we find are the following: 1) for metallicities Z <= 10-3, masses above ~ 4 Msun suffer complete CNO cycling in HBB, so that they show at the surface the result of this process, and the oxygen abundance is reduced; 2) most models suffer the third dredge up. Although carbon is processed to nitrogen by HBB, the oxygen burning is so strong in the lowest metallicities (2 x 10-4) that carbon becomes more abundant than oxygen: in other words, low-metallicity intermediate mass stars may show up as carbon stars due to the drastic oxygen burning; 3) if Globular Cluster stars are contaminated by matter processed through these phases, we must expect a non negligible helium enhancement in their composition: from a Big Bang abundance Y=0.24, e.g., we might expect an abundance Y=0.28. This may have no practical consequences if pollution concerns only the external parts of the stars, but is very important if the stars formed as a whole from a helium rich environment. 4) The lithium yields, although not important for galactic chemical evolution, are very interestingly close to the initial Big Bang abundance: processing by HBB is the only way in which we can obtain substantial amounts of gas which have gone through full CNO burning

  12. THE MASS-LOSS RETURN FROM EVOLVED STARS TO THE LARGE MAGELLANIC CLOUD. VI. LUMINOSITIES AND MASS-LOSS RATES ON POPULATION SCALES

    SciTech Connect

    Riebel, D.; Meixner, M.; Srinivasan, S.; Sargent, B.

    2012-07-01

    We present results from the first application of the Grid of Red Supergiant and Asymptotic Giant Branch ModelS (GRAMS) model grid to the entire evolved stellar population of the Large Magellanic Cloud (LMC). GRAMS is a pre-computed grid of 80,843 radiative transfer models of evolved stars and circumstellar dust shells composed of either silicate or carbonaceous dust. We fit GRAMS models to {approx}30,000 asymptotic giant branch (AGB) and red supergiant (RSG) stars in the LMC, using 12 bands of photometry from the optical to the mid-infrared. Our published data set consists of thousands of evolved stars with individually determined evolutionary parameters such as luminosity and mass-loss rate. The GRAMS grid has a greater than 80% accuracy rate discriminating between oxygen- and carbon-rich chemistry. The global dust injection rate to the interstellar medium (ISM) of the LMC from RSGs and AGB stars is on the order of 2.1 Multiplication-Sign 10{sup -5} M{sub Sun} yr{sup -1}, equivalent to a total mass injection rate (including the gas) into the ISM of {approx}6 Multiplication-Sign 10{sup -3} M{sub Sun} yr{sup -1}. Carbon stars inject two and a half times as much dust into the ISM as do O-rich AGB stars, but the same amount of mass. We determine a bolometric correction factor for C-rich AGB stars in the K{sub s} band as a function of J - K{sub s} color, BC{sub K{sub s}}= -0.40(J-K{sub s}){sup 2} + 1.83(J-K{sub s}) + 1.29. We determine several IR color proxies for the dust mass-loss rate (M-dot{sub d}) from C-rich AGB stars, such as log M-dot{sub d} = (-18.90/((K{sub s}-[8.0])+3.37) - 5.93. We find that a larger fraction of AGB stars exhibiting the 'long-secondary period' phenomenon are more O-rich than stars dominated by radial pulsations, and AGB stars without detectable mass loss do not appear on either the first-overtone or fundamental-mode pulsation sequences.

  13. Evolution, Nucleosynthesis, and Yields of AGB Stars at Different Metallicities. III. Intermediate-mass Models, Revised Low-mass Models, and the ph-FRUITY Interface

    NASA Astrophysics Data System (ADS)

    Cristallo, S.; Straniero, O.; Piersanti, L.; Gobrecht, D.

    2015-08-01

    We present a new set of models for intermediate-mass asymptotic giant branch (AGB) stars (4.0, 5.0, and 6.0 M⊙) at different metallicities (-2.15 ≤ [Fe/H] ≤ +0.15). This set integrates the existing models for low-mass AGB stars (1.3 ≤ M/M⊙ ≤ 3.0) already included in the FRUITY database. We describe the physical and chemical evolution of the computed models from the main sequence up to the end of the AGB phase. Due to less efficient third dredge up episodes, models with large core masses show modest surface enhancements. This effect is due to the fact that the interpulse phases are short and, therefore, thermal pulses (TPs) are weak. Moreover, the high temperature at the base of the convective envelope prevents it from deeply penetrating the underlying radiative layers. Depending on the initial stellar mass, the heavy element nucleosynthesis is dominated by different neutron sources. In particular, the s-process distributions of the more massive models are dominated by the 22Ne(α,n)25Mg reaction, which is efficiently activated during TPs. At low metallicities, our models undergo hot bottom burning and hot third dredge up. We compare our theoretical final core masses to available white dwarf observations. Moreover, we quantify the influence intermediate-mass models have on the carbon star luminosity function. Finally, we present the upgrade of the FRUITY web interface, which now also includes the physical quantities of the TP-AGB phase for all of the models included in the database (ph-FRUITY).

  14. The creation of AGB fallback shells

    NASA Astrophysics Data System (ADS)

    Chen, Zhuo; Frank, Adam; Blackman, Eric G.; Nordhaus, Jason

    2016-04-01

    The possibility that mass ejected during Asymptotic Giant Branch (AGB) stellar evolution phases falls back towards the star has been suggested in applications ranging from the formation of accretion discs to the powering of late-thermal pulses. In this paper, we seek to explicate the properties of fallback flow trajectories from mass-loss events. We focus on a transient phase of mass ejection with sub-escape speeds, followed by a phase of a typical AGB wind. We solve the problem using both hydrodynamic simulations and a simplified one-dimensional analytic model that matches the simulations. For a given set of initial wind characteristics, we find a critical shell velocity that distinguishes between `shell fallback' and `shell escape'. We discuss the relevance of our results for both single and binary AGB stars. In particular, we discuss how our results help to frame further studies of fallback as a mechanism for forming the substantial population of observed post-AGB stars with dusty discs.

  15. On the Relation between the Mysterious 21 μm Emission Feature of Post-asymptotic Giant Branch Stars and Their Mass-loss Rates

    NASA Astrophysics Data System (ADS)

    Mishra, Ajay; Li, Aigen; Jiang, B. W.

    2016-07-01

    Over two decades ago, a prominent, mysterious emission band peaking at ˜20.1 μm was serendipitously detected in four preplanetary nebulae (PPNe; also known as “protoplanetary nebulae”). To date, this spectral feature, designated as the “21 μm” feature, has been seen in 27 carbon-rich PPNe in the Milky Way and the Magellanic Clouds. The nature of its carriers remains unknown although many candidate materials have been proposed. The 21 μm sources also exhibit an equally mysterious, unidentified emission feature peaking at 30 μm. While the 21 μm feature is exclusively seen in PPNe, a short-lived evolutionary stage between the end of the asymptotic giant branch (AGB) and planetary nebula (PN) phases, the 30 μm feature is more commonly observed in all stages of stellar evolution from the AGB through PPN to PN phases. We derive the stellar mass-loss rates (\\dot{M}) of these sources from their infrared (IR) emission, using the “2-DUST” radiative transfer code for axisymmetric dusty systems which allows one to distinguish the mass-loss rates of the AGB phase ({\\dot{M}}{AGB}) from that of the superwind ({\\dot{M}}{SW}) phase. We examine the correlation between {\\dot{M}}{AGB} or {\\dot{M}}{SW} and the fluxes emitted from the 21 and 30 μm features. We find that both features tend to correlate with {\\dot{M}}{AGB}, suggesting that their carriers are probably formed in the AGB phase. The nondetection of the 21 μm feature in AGB stars suggests that, unlike the 30 μm feature, the excitation of the carriers of the 21 μm feature may require ultraviolet photons which are available in PPNe but not in AGB stars.

  16. Intermediate Luminosity Transients: their connection to Massive Stars, Episodic Mass Loss, and Supernovae

    NASA Astrophysics Data System (ADS)

    Prieto, Jose

    2013-06-01

    I will discuss a growing class of optical transients with typical peak luminosities between novae and supernovae. I will present their observational properties and their links to evolved massive stars, including the full range from massive AGB stars (8-10 Mo) to the most massive stars (> 100 Mo) like Eta Carinae. I will put their observational properties in the context of propsed physical mechanisms, including episodic mass-loss events, stellar mergers, and supernovae.

  17. Mass loss of massive stars

    NASA Astrophysics Data System (ADS)

    Martins, F.

    2015-12-01

    In this contribution we review the properties of the winds of massive stars. We focus on OB stars, red supergiants, Luminous Blue Variables (LBVs) and Wolf-Rayet stars. For each type of star, we summarize the main wind properties and we give a brief description of the physical mechanism(s) responsible for mass loss.

  18. Atmospheric structure and mass loss in Miras

    NASA Astrophysics Data System (ADS)

    Hinkle, Kenneth H.; Lebzelter, Thomas; Straniero, Oscar

    2016-07-01

    The cool molecular region of late-type stellar atmospheres, the ‘MOLsphere’ located between the photosphere and expanding circumstellar shell, is explored by using time series of near-IR spectra of one large amplitude AGB (Mira) variable. The ∼⃒1400 K MOLsphere of the Mira R Cas is shown to undergo large amplitude velocity changes that are aperiodic with time scales many times longer than the photospheric pulsation. The mass of the MOLsphere is ∼⃒3×10‑5 M⊙. Initial analysis suggests that MOLsphere is thin compared to the stellar radius.

  19. To be or not to be asymmetric? VLTI and the mass loss geometry of red giants

    NASA Astrophysics Data System (ADS)

    Paladini, Claudia; Klotz, Daniela; Sacuto, Stephane; Hron, Josef; Wittkowski, Markus; Lagadec, Eric; Verhoelst, Tijl; Jorissen, Alain; Richichi, Andrea; Groenewegen, Martin; Olofsson, Hans; Kerschbaum, Franz

    2012-07-01

    The mass-loss process is a key ingredient for our understanding in many fields of astrophysics, including stellar evolution and the enrichment of the interstellar medium (ISM) via stellar yields. We combined the capability of the VLTI/MIDI and VLT/VISIR instruments with very recent Herschel/PACS observations to characterize the geometry of mass loss from evolved red giants on the Asymptotic Giant Branch (AGB) at various scales. This paper describes the sample of objects, the observing strategy, the tool for the interpretation, and preliminary MIDI results for two targets: U Ant and θ Aps.

  20. Why Galaxies Care about AGB Stars: Setting the Stage

    NASA Astrophysics Data System (ADS)

    Renzini, A.

    2015-08-01

    In this introduction to the Third Congress of Vienna on asymptotic giant branch (AGB) stars, I first try to highlight why it is so hard to cope with the AGB evolutionary phase. This phase is indeed dominated by three main physical processes concerning bulk motions of matter inside/around stars, namely envelope convection, mixing, and mass loss. They are inextricably interlaced with each other in a circular sequence of reactions and counter-reactions which has so far undermined our attempts at calibrating such processes independent of one another. The second part of this introduction is focused on globular clusters, illustrating how they came to be a new frontier for AGB evolution and a new opportunity to understand it.

  1. Pulsation, mass loss, and evolution of upper asymptotic giant branch stars

    NASA Astrophysics Data System (ADS)

    Bedijn, P. J.

    1988-10-01

    It now seems observationally well established that mass loss plays an important role in the evolution of stars on the upper asymptotic giant branch (AGB), a phase which all stars with main sequence masses up to 8 Msun go through. Observations of outflowing circumstellar material around Miras and long period OH/IR variables infer mass loss rates of a few times 10-7 Msunyr-1 for the Miras up to more than 10-4 Msunyr-1for the OH/IR variables. If the Miras and the OH/IR variables represent subsequent phases in the evolution of a single star then the relative scarcity of OH/IR variables tells us that the phase during which rapid mass loss occurs (the OH/IR star phase) must be shorter than the phase of more modest mass loss (the Mira phase). At present two scenarios exist for the evolution of the mass loss rate from being modest during the Mira phase to being very large during the OH/IR star phase. In one scenario the large increase in the mass loss rate is thought to occur suddenly due to a switch in the pulsation mode; whereas Miras are thought to pulsate in the first overtone the OH/IR variables with periods roughly two times longer should pulsate in the fundamental mode. The number of stars showing 1612 MHz OH emission as a function of the OH luminosity, however, is observed to be a continuous distribution over quite a large range in OH luminosity. In the second scenario this is interpreted to mean a continuous accelerated increase of the OH luminosity and of the mass loss rate from small to large values for a single star. We (re)propose that stellar pulsation in a single mode in combination with radiation pressure on dust causes the mass loss in all stars on the upper AGB, whether Miras or OH/IR variables. We derive an expression for the mass loss rate in terms of the basic stellar parameters mass and radius. We show that this expression leads to a time evolution of the mass loss rate in accord with that found by the authors of the second scenario. We present a

  2. From Nuclei to Dust Grains: How the AGB Machinery Works

    NASA Astrophysics Data System (ADS)

    Gobrecht, D.; Cristallo, S.; Piersanti, L.

    2015-12-01

    With their circumstellar envelopes AGB stars are marvelous laboratories to test our knowledge of microphysics (opacities, equation of state), macrophysics (convection, rotation, stellar pulsations, magnetic fields) and nucleosynthesis (nuclear burnings, slow neutron capture processes, molecules and dust formation). Due to the completely different environments those processes occur, the interplay between stellar interiors (dominated by mixing events like convection and dredge-up episodes) and stellar winds (characterized by dust formation and wind acceleration) is often ignored. We intend to develop a new approach involving a transition region, taking into consideration hydrodynamic processes which may drive AGB mass-loss. Our aim is to describe the process triggering the mass-loss in AGB stars with different masses, metallicities and chemical enrichments, possibly deriving a velocity field of the outflowing matter. Moreover, we intend to construct an homogeneous theoretical database containing detailed abundances of atomic and molecular species produced by these objects. As a long term goal, we will derive dust production rates for silicates, alumina and silicon carbides, in order to explain laboratory measurements of isotopic ratios in AGB dust grains.

  3. THE MASS LOSS RETURN FROM EVOLVED STARS TO THE LARGE MAGELLANIC CLOUD: EMPIRICAL RELATIONS FOR EXCESS EMISSION AT 8 AND 24 {mu}m

    SciTech Connect

    Srinivasan, Sundar; Meixner, Margaret; Leitherer, Claus; Vijh, Uma; Gordon, Karl D.; Sewilo, Marta; Volk, Kevin; Blum, Robert D.; Harris, Jason; Babler, Brian L.; Bracker, Steve; Meade, Marilyn; Block, Miwa; Engelbracht, Charles W.; For, Bi-Qing; Misselt, Karl A.; Cohen, Martin; Hora, Joseph L.; Indebetouw, Remy; Markwick-Kemper, Francisca

    2009-06-15

    We present empirical relations describing excess emission from evolved stars in the Large Magellanic Cloud (LMC) using data from the Spitzer Space Telescope Surveying the Agents of a Galaxy's Evolution (SAGE) survey which includes the Infrared Array Camera (IRAC) 3.6, 4.5, 5.8, and 8.0 {mu}m and Multiband Imaging Photometer (MIPS) 24, 70, and 160 {mu}m bands. We combine the SAGE data with the Two Micron All Sky Survey (2MASS; J, H, and K {sub s}) and the optical Magellanic Cloud Photometric Survey (MCPS; U, B, V, and I) point source catalogs in order to create complete spectral energy distributions (SEDs) of the asymptotic giant branch (AGB) star candidates in the LMC. AGB star outflows are among the main producers of dust in a galaxy, and this mass loss results in an excess in the fluxes observed in the 8 and 24 {mu}m bands. The aim of this work is to investigate the mass loss return by AGB stars to the interstellar medium of the LMC by studying the dependence of the infrared excess flux on the total luminosity. We identify oxygen-rich, carbon-rich, and extreme AGB star populations in our sample based on their 2MASS and IRAC colors. The SEDs of oxygen- and carbon-rich AGB stars are compared with appropriate stellar photosphere models to obtain the excess flux in all the IRAC bands and the MIPS 24 {mu}m band. Extreme AGB stars are dominated by circumstellar emission at 8 and 24 {mu}m; thus we approximate their excesses with the flux observed in these bands. We find about 16,000 O-rich, 6300 C-rich, and 1000 extreme sources with reliable 8 {mu}m excesses, and about 4500 O-rich, 5300 C-rich, and 960 extreme sources with reliable 24 {mu}m excesses. The excesses are in the range 0.1 mJy to 5 Jy. The 8 and 24 {mu}m excesses for all three types of AGB candidates show a general increasing trend with luminosity. The color temperature of the circumstellar dust derived from the ratio of the 8 and 24 {mu}m excesses decreases with an increase in excess, while the 24 {mu

  4. HIRAS images of fossil dust shells around AGB stars

    NASA Technical Reports Server (NTRS)

    Waters, L. B. F. M.; Kester, Do J. M.; Bontekoe, Tj. Romke; Loup, C.

    1994-01-01

    We present high resolution HIRAS 60 and 100 micron images of AGB stars surrounded by fossil dust shells. Resolving the extended emission of the circumstellar dust allows a determination of the mass loss history of the star. We show that the geometry of the 60 micron emission surrounding HR 3126 agrees well with that of the optical reflection nebula. The emission around the carbon star U Hya is resolved into a central point source and a ring of dust, and the mass loss rate in the detached shell is 70 times higher than the current mass loss rate.

  5. High rotational CO lines in post-AGB stars and PNe

    NASA Technical Reports Server (NTRS)

    Justtanont, K.; Tielens, Alexander G. G. M.; Skinner, C. J.; Haas, Michael R.

    1995-01-01

    A significant fraction of a star's initial mass is lost while it is on the Asymptotic Giant Branch (AGB). Mass loss rates range from 10(exp -7) solar mass/yr for early AGB stars to a few 10(exp -4) solar mass/yr for stars at the tip of the AGB. Dust grains condense from the outflow as the gas expands and form a dust shell around the central star. A superwind (approximately 10(exp -4) to 10(exp -3) solar mass/yr) is thought to terminate the AGB phase. In the post-AGB phase, the star evolves to a higher effective temperature, the mass loss decreases (approximately 10(exp -8) solar mass/yr), but the wind velocity increases (approximately 1000 km/s). During this evolution, dust and gas are exposed to an increasingly harsher radiation field and when T(sub eff) reaches about 30,000 K, the nebula is ionized and becomes a planetary nebula (PN). Photons from the central star can create a photodissociation region (PDR) in the expanding superwind. Gas can be heated through the photoelectric effect working on small grains and polycyclic aromatic hydrocarbons (PAH's). This gas can cool via the atomic fine structure lines of O I (63 microns and 145 microns) and C II (158 microns), as well as the rotational lines of CO. In the post-AGB phase, the fast wind from the central star will interact with the material ejected during the AGB phase. The shock caused by this interaction will dissociate and heat the gas. This warm gas will cool through atomic fine structure lines of O I and the rotational lines of (newly formed) CO.

  6. Winds of Binary AGB Stars as Observed by Herschel

    NASA Astrophysics Data System (ADS)

    Mayer, A.; Jorissen, A.; Kerschbaum, F.; Ottensamer, R.; Mečina, M.; Paladini, C.; Cox, N. L. J.; Nowotny, W.; Aringer, B.; Pourbaix, D.; Mohamed, S.; Siopis, C.; Groenewegen, M. A. T.

    2015-08-01

    We present Herschel/PACS observations of the large-scale environments of binary AGB stars as part of the Mass-loss of Evolved StarS (MESS) sample. From the literature we found 18 of the objects to be members of physically bound multiple systems. Several show a large-scale far-IR emission which differs significantly from spherical symmetry. A probable cause is the gravitational force of the companion on the stellar AGB wind and the mass-losing star itself. A spiral pattern is thereby imprinted in the dusty stellar wind. The most remarkable structures are found around o Ceti, W Aquilæ, R Aquarii, and π1 Gruis. The environments of o Cet and W Aql show a spiral pattern while the symbiotic nature of R Aqr is revealed as two opposing arms which reflect a nova outburst. The emission around π1 Gru is dominated by two structures, a disk and an arc, which are presumably not caused by the same companion. We found evidence that π1 Gru is a hierarchical triple system in which a close companion attracts the AGB wind onto the orbital plane and the outer companion forms a spiral arm. These far-IR observations underline the role of a companion as a major external influence in creating asymmetric winds in the AGB phase, even before the star becomes a planetary nebula (PN).

  7. Mass-loss From Evolved Stellar Populations In The Large Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Riebel, David

    2012-01-01

    I have conducted a study of a sample of 30,000 evolved stars in the Large Magellanic Cloud (LMC) and 6,000 in the Small Magellanic Cloud (SMC), covering their variability, mass-loss properties, and chemistry. The initial stages of of my thesis work focused on the infrared variability of Asymptotic Giant Branch (AGB) stars in the LMC. I determined the period-luminosity (P-L) relations for 6 separate sequences of 30,000 evolved star candidates at 8 wavelengths, as a function of photometrically assigned chemistry, and showed that the P-L relations are different for different chemical populations (O-rich or C-rich). I also present results from the Grid of Red supergiant and Asymptotic giant branch star ModelS (GRAMS) radiative transfer (RT) model grid applied to the evolved stellar population of the LMC. GRAMS is a pre-computed grid of RT models of RSG and AGB stars and surrounding circumstellar dust. Best-fit models are determined based on 12 bands of photometry from the optical to the mid-infrared. Using a pre-computed grid, I can present the first reasonably detailed radiative transfer modeling for tens of thousands of stars, allowing me to make statistically accurate estimations of the carbon-star luminosity function and the global dust mass return to the interstellar medium from AGB stars, both key parameters for stellar population synthesis models to reproduce. In the SAGE-Var program, I used the warm Spitzer mission to take 4 additional epochs of observations of 7500 AGB stars in the LMC and SMC. These epochs, combined with existing data, enable me to derive mean fluxes at 3.6 and 4.5 microns, that will be used for tighter constraints for GRAMS, which is currently limited by the variability induced error on the photometry. This work is support by NASA NAG5-12595 and Spitzer contract 1415784.

  8. On the formation of molecules and solid-state compounds from the AGB to the PN phases

    NASA Astrophysics Data System (ADS)

    García-Hernández, D. A.; Manchado, A.

    2016-07-01

    During the asymptoyic giant branch (AGB) phase, different elements are dredge- up to the stellar surface depending on progenitor mass and metallicity. When the mass loss increases at the end of the AGB, a circumstellar dust shell is formed, where different (C-rich or O-rich) molecules and solid-state compounds are formed. These are further processed in the transition phase between AGB stars and planetary nebulae (PNe) to create more complex organic molecules and inorganic solid-state compounds (e.g., polycyclic aromatic hydrocarbons, fullerenes, and graphene precursors in C-rich environments and oxides and crystalline silicates in O-rich ones). We present an observational review of the different molecules and solid-state materials that are formed from the AGB to the PN phases. We focus on the formation routes of complex fullerene (and fullerene-based) molecules as well as on the level of dust processing depending on metallicity.

  9. Geometry of the Dusty Mass Loss from Low- to Intermediate Mass Stars

    NASA Astrophysics Data System (ADS)

    Tomasino, Rachael; Ueta, Toshiya; Yamamura, Issei; Takita, Satoshi; Izumiura, Hideyuki

    2015-01-01

    Low- to intermediate-mass stars lose a significant fraction of their mass while they are on the asymptotic giant branch (AGB). The material ejected from the stellar photosphere forms a circumstellar envelope in its surroundings and this mass loss is considered to determine the final stages of their evolution. By studying the layers of the circumstellar envelope we are actually studying the footprint of the mass-loss history.AKARI is the first Japanese satellite dedicated to infrared astronomy, was launched in 2006, and in 2011, ended science operations. The main objective was to perform an all-sky survey with better spatial resolution and wider wavelength coverage than IRAS (Neugebauer et al. 1984), mapping the entire sky in six infrared bands from two focal plane instruments. Inserted within the continuous survey operation is the slow scan pointed observation mode. The MLHES (excavating Mass Loss History in Extended dust shells of Evolved Stars) data set was observed within this mode and used the FIS (Far Infrared Surveyor) focal plane instrument. The FIS detector has four photometric bands between 50 - 180 μm. Far-IR radiation is optically thin and thus the surface brightness distribution of the target circumstellar shells allows us to see the whole nebula volume along the line of sight.MLHES is the largest data set to date for the analysis of circumstellar dust around evolved low- to intermediate- mass stars and was designed to systematically investigate some of the open questions surrounding circumstellar dust while utilizing the benefits of far-IR radiation. What is the time evolution of the mass-loss rate? What is the geometry of the mass-loss process? How do the characteristics of the progenitor star effect the mass-loss?The work presented here focuses on the characterization of the geometric properties of the PSF subtracted images of the circumstellar material. By subtracting the PSF, we are able to obtain an undisturbed picture of the shape of the mass

  10. METAL-POOR STARS OBSERVED WITH THE MAGELLAN TELESCOPE. I. CONSTRAINTS ON PROGENITOR MASS AND METALLICITY OF AGB STARS UNDERGOING s-PROCESS NUCLEOSYNTHESIS

    SciTech Connect

    Placco, Vinicius M.; Rossi, Silvia; Frebel, Anna; Beers, Timothy C.; Karakas, Amanda I.; Kennedy, Catherine R.; Christlieb, Norbert; Stancliffe, Richard J.

    2013-06-20

    We present a comprehensive abundance analysis of two newly discovered carbon-enhanced metal-poor (CEMP) stars. HE 2138-3336 is a s-process-rich star with [Fe/H] = -2.79, and has the highest [Pb/Fe] abundance ratio measured thus far, if non-local thermodynamic equilibrium corrections are included ([Pb/Fe] = +3.84). HE 2258-6358, with [Fe/H] = -2.67, exhibits enrichments in both s- and r-process elements. These stars were selected from a sample of candidate metal-poor stars from the Hamburg/ESO objective-prism survey, and followed up with medium-resolution (R {approx} 2000) spectroscopy with GEMINI/GMOS. We report here on derived abundances (or limits) for a total of 34 elements in each star, based on high-resolution (R {approx} 30, 000) spectroscopy obtained with Magellan-Clay/MIKE. Our results are compared to predictions from new theoretical asymptotic giant branch (AGB) nucleosynthesis models of 1.3 M{sub Sun} with [Fe/H] = -2.5 and -2.8, as well as to a set of AGB models of 1.0 to 6.0 M{sub Sun} at [Fe/H] = -2.3. The agreement with the model predictions suggests that the neutron-capture material in HE 2138-3336 originated from mass transfer from a binary companion star that previously went through the AGB phase, whereas for HE 2258-6358, an additional process has to be taken into account to explain its abundance pattern. We find that a narrow range of progenitor masses (1.0 {<=} M(M{sub Sun }) {<=} 1.3) and metallicities (-2.8 {<=} [Fe/H] {<=}-2.5) yield the best agreement with our observed elemental abundance patterns.

  11. Evolution and mixing on the AGB

    SciTech Connect

    Lattanzio, J.C.

    1988-07-27

    It is now well known that Nature can make Carbon stars at lower luminosities than can (human) theorists. A number of workers, stimulated by this challenge, have been attracted to the problem. In this paper I review recent evolutionary models of relatively low mass AGB stars, with emphasis placed on the mixing of carbon to the stellar surface. In particular I discuss some recent improvements in the physics used to construct stellar models. These topics include: breathing pulses of the convective core found during exhaustion of the core helium supply; the effects of carbon recombination; the occurrence of semiconvection in the region between the two nuclear burning shells, and the importance of mass loss. It appears that different effects may operate at different stellar masses and abundances. Recent calculations have successfully produced models of low luminosity Carbon stars. The strengths and weaknesses of these models will be contrasted. 60 refs., 5 figs.

  12. Dusty wind of W Hydrae. Multi-wavelength modelling of the present-day and recent mass loss

    NASA Astrophysics Data System (ADS)

    Khouri, T.; Waters, L. B. F. M.; de Koter, A.; Decin, L.; Min, M.; de Vries, B. L.; Lombaert, R.; Cox, N. L. J.

    2015-05-01

    Context. Low- and intermediate-mass stars go through a period of intense mass-loss at the end of their lives, during the asymptotic giant branch (AGB) phase. While on the AGB a significant part, or even most, of their initial mass is expelled in a stellar wind. This process controls the final stages of the evolution of these stars and contributes to the chemical evolution of galaxies. However, the wind-driving mechanism of AGB stars is not yet well understood, especially so for oxygen-rich sources. Characterizing both the present-day mass-loss rate and wind structure and the evolution of the mass-loss rate of such stars is paramount to advancing our understanding of this processes. Aims: We study the dusty wind of the oxygen-rich AGB star W Hya to understand its composition and structure and shed light on the mass-loss mechanism. Methods: We modelled the dust envelope of W Hya using an advanced radiative transfer code. We analysed our dust model in the light of a previously calculated gas-phase wind model and compared it with measurements available in the literature, such as infrared spectra, infrared images, and optical scattered light fractions. Results: We find that the dust spectrum of W Hya can partly be explained by a gravitationally bound dust shell that probably is responsible for most of the amorphous Al2O3 emission. The composition of the large (~0.3 μm) grains needed to explain the scattered light cannot be constrained, but probably is dominated by silicates. Silicate emission in the thermal infrared was found to originate from beyond 40 AU from the star. In our model, the silicates need to have substantial near-infrared opacities to be visible at such large distances. The increase in near-infrared opacity of the dust at these distances roughly coincides with a sudden increase in expansion velocity as deduced from the gas-phase CO lines. The dust envelope of W Hya probably contains an important amount of calcium but we were not able to obtain a dust

  13. CLASSICAL CEPHEIDS REQUIRE ENHANCED MASS LOSS

    SciTech Connect

    Neilson, Hilding R.; Langer, Norbert; Izzard, Robert; Engle, Scott G.; Guinan, Ed

    2012-11-20

    Measurements of rates of period change of Classical Cepheids probe stellar physics and evolution. Additionally, better understanding of Cepheid structure and evolution provides greater insight into their use as standard candles and tools for measuring the Hubble constant. Our recent study of the period change of the nearest Cepheid, Polaris, suggested that it is undergoing enhanced mass loss when compared to canonical stellar evolution model predictions. In this work, we expand the analysis to rates of period change measured for about 200 Galactic Cepheids and compare them to population synthesis models of Cepheids including convective core overshooting and enhanced mass loss. Rates of period change predicted from stellar evolution models without mass loss do not agree with observed rates, whereas including enhanced mass loss yields predicted rates in better agreement with observations. This is the first evidence that enhanced mass loss as suggested previously for Polaris and {delta} Cephei must be a ubiquitous property of Classical Cepheids.

  14. Magnetic fields around AGB stars and Planetary Nebulae

    NASA Astrophysics Data System (ADS)

    Vlemmings, W. H. T.

    2014-08-01

    Stars with a mass up to a few solar masses are one of the main contributors to the enrichment of the interstellar medium in dust and heavy elements. However, while significant progress has been made, the process of the mass-loss responsible for this enrichment is still not exactly known and forces beyond radiation pressure might be required. Often, the mass lost in the last phases of the stars life will become a spectacular planetary nebula. The shaping process of often strongly a-spherical PNe is equally elusive. Both binaries and magnetic fields have been suggested to be possible agents although a combination of both might also be a natural explanation. Here I review the current evidence for magnetic fields around AGB and post-AGB stars pre-Planetary Nebulae and PNe themselves. Magnetic fields appear to be ubiquitous in the envelopes of apparently single stars, challenging current ideas on its origin, although we have found that binary companions could easily be hidden from view. There are also strong indications of magnetically collimated outflows from post-AGB/pre-PNe objects supporting a significant role in shaping the circumstellar envelope.

  15. Winds of M- and S-type AGB stars: an unorthodox suggestion for the driving mechanism

    NASA Astrophysics Data System (ADS)

    Höfner, S.; Andersen, A. C.

    2007-04-01

    Context: Current knowledge suggests that the dust-driven wind scenario provides a realistic framework for understanding mass loss from C-rich AGB stars. For M-type objects, however, recent detailed models demonstrate that radiation pressure on silicate grains is not sufficient to drive the observed winds, contrary to previous expectations. Aims: In this paper, we suggest an alternative mechanism for the mass loss of M-type AGB stars, involving the formation of both carbon and silicate grains due to non-equilibrium effects, and we study the viability of this scenario. Methods: We model the dynamical atmospheres and winds of AGB stars by solving the coupled system of frequency-dependent radiation hydrodynamics and time-dependent dust formation, using a parameterized description of non-equilibrium effects in the gas phase. This approach allows us to assess under which circumstances it is possible to drive winds with small amounts of carbon dust and to get silicate grains forming in these outflows at the same time. Results: The properties of the resulting wind models, such as mass-loss rates and outflow velocities, are well within the observed limits for M-type AGB stars. Furthermore, according to our results, it is quite unlikely that significant amounts of silicate grains will condense in a wind driven by a force totally unrelated to dust formation, as the conditions in the upper atmosphere and wind acceleration region put strong constraints on grain growth. Conclusions: .The proposed scenario provides a natural explanation for the observed similarities in wind properties of M-type and C-type AGB stars and implies a smooth transition for stars with increasing carbon abundance, from solar-composition to C-rich AGB stars, possibly solving the longstanding problem of the driving mechanism for stars with a C/O close to one.

  16. Mass loss and dust formation around oxygen-rich evolved stars

    NASA Astrophysics Data System (ADS)

    Kemper, F.

    2002-09-01

    This work is a study of the formation of dust around oxygen-rich evolved stars, in correlation with the physical conditions in this environment. ISO SWS and LWS spectroscopy has been analysed, and several mineral and molecular species are identified. For two evolved stars: OH/IR star OH 127.8+0.0 and planetary nebula NGC 6302, the spectral energy distribution has been fitted. Metallic iron and carbonates are identified as new dust components. In addition, the degree of crystallinity of silicates has been studied as a function of mass-loss rate. Finally, submm observations of rotational transitions of CO have been analysed to study the mass-loss history of oxygen-rich AGB stars.

  17. Wind Acceleration in AGB Stars: Solid Ground and Loose Ends

    NASA Astrophysics Data System (ADS)

    Höfner, S.

    2015-08-01

    The winds of cool luminous AGB stars are commonly assumed to be driven by radiative acceleration of dust grains which form in the extended atmospheres produced by pulsation-induced shock waves. The dust particles gain momentum by absorption or scattering of stellar photons, and they drag along the surrounding gas particles through collisions, triggering an outflow. This scenario, here referred to as Pulsation-Enhanced Dust-DRiven Outflow (PEDDRO), has passed a range of critical observational tests as models have developed from empirical and qualitative to increasingly self-consistent and quantitative. A reliable theory of mass loss is an essential piece in the bigger picture of stellar and galactic chemical evolution, and central for determining the contribution of AGB stars to the dust budget of galaxies. In this review, I discuss the current understanding of wind acceleration and indicate areas where further efforts by theorists and observers are needed.

  18. Pulsation and mass loss in Mira variables

    NASA Technical Reports Server (NTRS)

    Wood, P. R.

    1980-01-01

    The behavior of pulsation in the outer layers of a typical Mira variable was studied in the adiabatic and isothermal limits. A shock wave propagates outward once per period and the radial velocity obtained from observations of hydrogen emission lines is identified with the velocity of gas in the post shock region. In the adiabatic case, mass loss in the form of a steady stellar wind was produced. In the isothermal case, no continuous mass loss was produced but occasional ejection of shells occur. Pulsation introduced into a star undergoing steady mass loss as a result of radiation pressure acting on grains caused the mass loss rate to increase by a factor of approximately 40, while the terminal velocity of the flow was almost unaltered.

  19. Mass loss from warm giants: Magnetic effects

    NASA Technical Reports Server (NTRS)

    Mullan, D. J.

    1980-01-01

    Among warm giant stars, rapid mass loss sets in along a well defined velocity dividing line (VDL). Hot corona also disappear close to the VDL and thermal pressure cannot drive the observed rapid mass loss in these stars. The VDL may be associated with magnetic fields changing from closed to open. Such a change is consistent with the lack of X-rays from late-type giants. A magnetic transition locus based on Pneuman's work on helmet streamer stability agrees well with the empirical VDL. The change from closed to open fields not only makes rapid mass loss possible, but also contributes to energizing the mass loss in the form of discrete bubbles.

  20. Mass loss in red giants and supergiants

    NASA Technical Reports Server (NTRS)

    Sanner, F.

    1975-01-01

    The circumstellar envelopes surrounding late-type giants and supergiants were studied using high resolution, photoelectric scans of strong optical resonance lines. A method for extracting the circumstellar from the stellar components of the lines allowed a quantitative determination of the physical conditions in the envelopes and the rates of mass loss at various positions in the red giant region of the HR diagram. The observed strengthening of the circumstellar spectrum with increasing luminosity and later spectral type is probably caused by an increase in the mass of the envelopes. The mass loss rate for individual stars is proportional to the visual luminosity; high rates for the supergiants suggest that mass loss is important in their evolution. The bulk of the mass return to the interstellar medium in the red giant region comes from the normal giants, at a rate comparable to that of planetary nebulae.

  1. Coagulation and fragmentation with discrete mass loss

    NASA Astrophysics Data System (ADS)

    Blair, Pamela N.; Lamb, Wilson; Stewart, Iain W.

    2007-05-01

    A nonlinear integro-differential equation that models a coagulation and multiple fragmentation process in which discrete fragmentation mass loss can occur is examined using the theory of strongly continuous semigroups of operators. Under the assumptions that the coagulation kernel is bounded and the fragmentation rate function a satisfies a linear growth condition, global existence and uniqueness of solutions that lose mass in accordance with the model are established. In the case when no coagulation is present and the fragmentation process is governed by power-law kernels, an explicit formula is given for the substochastic semigroup associated with the resulting mass-loss fragmentation equation.

  2. Instability & Mass Loss near the Eddington Limit

    NASA Astrophysics Data System (ADS)

    Owocki, S. P.; Shaviv, N. J.

    We review the physics of continuum-driven mass loss and its likely role in η Carinae and LBVs. Unlike a line-driven wind, which is inherently limited by self-shadowing, continuum driving can in principle lead to mass-loss rates up to the "photon-tiring" limit, for which the entire luminosity is expended in lifting the outflow. We discuss how instabilities near the Eddington limit give rise to a clumped atmosphere, and how the associated "porosity" can regulate a continuum-driven flow. We also summarize recent time-dependent simulations in which a mass flow stagnates because it exceeds the tiring limit, leading to complex time-dependent inflow and outflow regions. Porosity-regulated continuum driving in super-Eddington epochs can probably explain the large, near tiring-limit mass loss inferred for LBV giant eruptions. However, while these extreme flows can persist over dynamically long periods, they cannot be sustained for an evolutionary timescale; so ultimately it is stellar structure and evolution that sets the overall mass loss.

  3. A Spitzer study of the mass-loss and infrared variability properties of Asymptotic Giant Branch stars in the Magellanic Clouds

    NASA Astrophysics Data System (ADS)

    Riebel, David

    The Asymptotic Giant Branch (AGB) is one of the most interesting, and least understood, phases of stellar evolution. The fate of approximately solar mass stars as they exhaust their nuclear fuel for the final time, these stars are also one of the universe's primary sources for many heavy elements, such as carbon and oxygen. We have assembled a sample of ˜30,000 AGB stars in the Large Magellanic Cloud (LMC) with multi-wavelength data ranging from the ultraviolet to the mid-infrared, and multi-epoch data spanning 5 years. This dataset allows us to probe the variability and mass-loss properties of AGB stars at population scales, a valuable contribution to studies of stellar evolution and the mass budget of the interstellar medium (ISM). We combine variability information from the MAssive Compact Halo Objects (MACHO; Alcock et al. 1997) microlensing survey with infrared photometry from the Spitzer Space Telescope legacy program Surveying the Agents of Galaxy Evolution (SAGE; Meixner et al. 2006) to determine the infrared period-magnitude relationships for three evolutionary classes of AGB stars at 8 different wavelengths. We find that the most evolved AGB stars are pulsating in the fundamental and first overtone, while less evolved stars are concentrated in higher-overtone modes. We show that the slope of the period-magnitude relationship becomes steeper for more evolved stars, at all wavelengths. Using a grid of radiative transfer models of circumstellar dust shells (GRAMS; Sargent et al. 2011; Srinivasan et al. 2011) and photometry in 12 bands ranging from the ultraviolet to the infrared, we calculated individual bolometric luminosities and dust mass-loss rates for each AGB star in the LMC. This allowed us to calculate the total dust injection to the interstellar medium from these stars via direct summation. We find that the total mass injection rate (gas and dust) from AGB stars into the ISM of the LMC is ˜5x10 --3 M⊙ yr--1, and that carbon-rich AGB stars and

  4. Optically bright Post-AGB stars in the Magellanic Clouds

    NASA Astrophysics Data System (ADS)

    Kamath, D.; Wood, P. R.; Van Winckel, H.

    2014-04-01

    Post-AGB stars are low- to intermediate-mass stars in a rapid transition from the AGB phase to the Planetary Nebula (PN) phase. Post-AGB stars bear signatures of the structural and chemical composition changes that occur during the AGB phase of evolution and therefore can be used to constrain AGB models and also provide insight to the formation of PNes. In the Galaxy, the luminosities (and hence initial masses) of the diverse group of post-AGB candidates are badly affected by their unknown distances, making it difficult to use the observational characteristics of these interesting objects to throw light on the poorly-understood late stages of stellar evolution. In this talk, I will present the new results of a systematic search for post-AGB candidates in the Magellanic Clouds which became possible after the release of deep infrared surveys such as mid-infrared LMC and SMC Spitzer surveys. The catalog of post-AGB candidates in the Magellanic Clouds has been created firstly by selecting candidates based on the existence of a mid-infrared excess and secondly by obtaining low-resolution optical spectra. The optical spectra and broadband photometry were used to derive luminosities, effective temperatures and masses for the post-AGB candidates. Using a combination of colour criteria and SED analysis, we were able to classify between single and binary post-AGB objects. Binary post-AGB stars are likely to produce asymmetric PN (or bipolar PN). We also find that variability is displayed by several of the post-AGB candidates with the most common variability types being the Population II Cepheids (including RV-Tauri stars) and semi-regular variables. From the numbers of post-AGB candidates in the SMC and LMC, we were able to estimate evolutionary rates for the transient post-AGB phase. These catalogs of spectroscopically verified post-AGB candidates are a valuable resource for the study of late stages of single and binary star evolution as a function of initial mass and

  5. Nucleosynthesis in Super-AGB Stars

    NASA Astrophysics Data System (ADS)

    Doherty, C. L.; Gil-Pons, P.; Lugaro, M.; Lau, H. H. B.; Lattanzio, J. C.; Siess, L.; Campbell, S. W.; Petermann, I.

    2015-08-01

    Super-AGB stars reside in the mass range ˜ 6.5-10 M⊙ and are characterised by off-center carbon ignition prior to a thermally pulsing super-AGB phase. These stars can undergo from many tens to even thousands of thermal pulses and experience extreme nucleosynthetic conditions, with temperatures both at the base of the convective envelope and within the helium-burning intershell regions far higher than in their lower-mass counterparts. This can result in interesting nucleosynthesis from extreme hot bottom burning and also different heavy-element distributions caused by the high neutron density generated within the thermal pulse, with this material later mixed to the surface during third dredge-up events. We discuss recent nucleosynthetic yield results for super-AGB stars over the range of metallicity Z = 0.02 × 10-5 ([Fe/H] ˜ 0 to -3.3), and present a small suite of heavy element super-AGB star yield predictions. We also apply our nucleosynthetic results to examine the possible role of super-AGB stars as polluters of the anomalous stars within globular clusters.

  6. Adiabatic Mass Loss Model in Binary Stars

    NASA Astrophysics Data System (ADS)

    Ge, H. W.

    2012-07-01

    Rapid mass transfer process in the interacting binary systems is very complicated. It relates to two basic problems in the binary star evolution, i.e., the dynamically unstable Roche-lobe overflow and the common envelope evolution. Both of the problems are very important and difficult to be modeled. In this PhD thesis, we focus on the rapid mass loss process of the donor in interacting binary systems. The application to the criterion of dynamically unstable mass transfer and the common envelope evolution are also included. Our results based on the adiabatic mass loss model could be used to improve the binary evolution theory, the binary population synthetic method, and other related aspects. We build up the adiabatic mass loss model. In this model, two approximations are included. The first one is that the energy generation and heat flow through the stellar interior can be neglected, hence the restructuring is adiabatic. The second one is that he stellar interior remains in hydrostatic equilibrium. We model this response by constructing model sequences, beginning with a donor star filling its Roche lobe at an arbitrary point in its evolution, holding its specific entropy and composition profiles fixed. These approximations are validated by the comparison with the time-dependent binary mass transfer calculations and the polytropic model for low mass zero-age main-sequence stars. In the dynamical time scale mass transfer, the adiabatic response of the donor star drives it to expand beyond its Roche lobe, leading to runaway mass transfer and the formation of a common envelope with its companion star. For donor stars with surface convection zones of any significant depth, this runaway condition is encountered early in mass transfer, if at all; but for main sequence stars with radiative envelopes, it may be encountered after a prolonged phase of thermal time scale mass transfer, so-called delayed dynamical instability. We identify the critical binary mass ratio for the

  7. Mass Loss Rates of Fasting Polar Bears.

    PubMed

    Pilfold, Nicholas W; Hedman, Daryll; Stirling, Ian; Derocher, Andrew E; Lunn, Nicholas J; Richardson, Evan

    2016-01-01

    Polar bears (Ursus maritimus) have adapted to an annual cyclic regime of feeding and fasting, which is extreme in seasonal sea ice regions of the Arctic. As a consequence of climate change, sea ice breakup has become earlier and the duration of the open-water period through which polar bears must rely on fat reserves has increased. To date, there is limited empirical data with which to evaluate the potential energetic capacity of polar bears to withstand longer fasts. We measured the incoming and outgoing mass of inactive polar bears (n = 142) that were temporarily detained by Manitoba Conservation and Water Stewardship during the open-water period near the town of Churchill, Manitoba, Canada, in 2009-2014. Polar bears were given access to water but not food and held for a median length of 17 d. Median mass loss rates were 1.0 kg/d, while median mass-specific loss rates were 0.5%/d, similar to other species with high adiposity and prolonged fasting capacities. Mass loss by unfed captive adult males was identical to that lost by free-ranging individuals, suggesting that terrestrial feeding contributes little to offset mass loss. The inferred metabolic rate was comparable to a basal mammalian rate, suggesting that while on land, polar bears can maintain a depressed metabolic rate to conserve energy. Finally, we estimated time to starvation for subadults and adult males for the on-land period. Results suggest that at 180 d of fasting, 56%-63% of subadults and 18%-24% of adult males in this study would die of starvation. Results corroborate previous assessments on the limits of polar bear capacity to withstand lengthening ice-free seasons and emphasize the greater sensitivity of subadults to changes in sea ice phenology. PMID:27617359

  8. THE MASS-LOSS RETURN FROM EVOLVED STARS TO THE LARGE MAGELLANIC CLOUD. II. DUST PROPERTIES FOR OXYGEN-RICH ASYMPTOTIC GIANT BRANCH STARS

    SciTech Connect

    Sargent, Benjamin A.; Meixner, M.; Gordon, Karl D.; Srinivasan, S.; Kemper, F.; Woods, Paul M.; Tielens, A. G. G. M.; Speck, A. K.; Matsuura, M.; Bernard, J.-Ph.; Hony, S.; Marengo, M.; Sloan, G. C.

    2010-06-10

    {approx}52 times the stellar radius, respectively, with dust temperatures there of 900 K and 430 K, respectively, and with optical depths at 10 {mu}m through the shells of 0.095 and 0.012, respectively. The models compute the dust mass-loss rates for the two stars to be 2.0 x 10{sup -9} M{sub sun} yr{sup -1} and 2.3 x 10{sup -9} M{sub sun} yr{sup -1}, respectively. When a dust-to-gas mass ratio of 0.002 is assumed for SSTSAGE052206 and HV 5715, the dust mass-loss rates imply total mass-loss rates of 1.0 x 10{sup -6} M{sub sun} yr{sup -1} and 1.2 x 10{sup -6} M{sub sun} yr{sup -1}, respectively. These properties of the dust shells and stars, as inferred from our models of the two stars, are found to be consistent with properties observed or assumed by detailed studies of other O-rich AGB stars in the LMC and elsewhere.

  9. Variable X-Ray and UV emission from AGB stars: Accretion activity associated with binarity

    NASA Astrophysics Data System (ADS)

    Sahai, Raghvendra; Sanz-Forcada, Jorge; Sánchez Contreras, Carmen

    2016-07-01

    Almost all of our current understanding of the late evolutionary stages of (1 — 8) Mʘ stars is based on single-star models. However, binarity can drastically affect late stellar evolution, producing dramatic changes in the history and geometry of mass loss that occurs in stars as they evolve off the AGB to become planetary nebulae (PNe). A variety of binary models have been proposed, which can lead to the generation of accretion disks and magnetic fields, which in turn produce the highly collimated jets that have been proposed as the primary agents for the formation of bipolar and multipolar PNe. However, observational evidence of binarity in AGB stars is sorely lacking simply these stars are very luminous and variable, invalidating standard techniques for binary detection. Using an innovative technique of searching for UV emission from AGB stars with GALEX, we have identified a class of AGB stars with far- ultraviolet excesses (fuvAGB stars), that are likely candidates for active accretion associated with a binary companion. We have carried out a pilot survey for X-ray emission from fuvAGB stars. The X-ray fluxes are found to vary in a stochastic or quasi-periodic manner on roughly hour-long times-scales, and simultaneous UV observations show similar variations in the UV fluxes. We discuss several models for the X-ray emission and its variability and find that the most likely scenario for the origin of the X-ray (and FUV) emission involves accretion activity around a main-sequence companion star, with confinement by strong magnetic fields associated with the companion and/or an accretion disk around it.

  10. Detailed Modelling of the Circumstellar Envelope of the S-type AGB Star W Aquilae

    NASA Astrophysics Data System (ADS)

    Danilovich, T.; Bergman, P.; Justtanont, K.; Lombaert, R.; Maercker, M.; Olofsson, H.; Ramstedt, S.; Royer, P.

    2015-08-01

    We present new Herschel HIFI (de Graauw et al. 2010) and PACS (Poglitsch et al. 2010) sub-millimeter and far-infrared line observations of several molecular species towards the S-type AGB star W Aql. We use these observations, which probe a wide range of gas temperatures, to constrain the circumstellar properties of W Aql, including mass-loss rate and molecular abundances.

  11. The Transformation of an AGB Star to a Planetary Nebula: How the Journey Begins

    NASA Astrophysics Data System (ADS)

    Sahai, Raghvendra; Blumenfeld, C.; Morris, M.; S'anchez Contreras, C.; Claussen, M.

    2010-01-01

    We report the results from an HST imaging survey of a sample of late AGB stars with a detected history of extensive past mass-loss, i.e., those in which this process has now come to an end. The goal of this survey is to identify and characterise the earliest stages of the process that transforms these objects, first into bipolar or multipolar pre-planetary nebulae (PPNe), and then into similarly-shaped planetary nebulae. Since the cessation of mass-loss leads to the lack of hot dust close to the star, their thermal emission at short ( 25 micron) wavelengths, is expected to be lower than that for typical AGB stars. We have therefore used the IRAS 25 to 12 micron flux ratio, F25/F12 > 0.33 (but < 0.67 in order to exclude PPNe), to select a list of 60 such ``nascent pre-planetary nebulae" (or nPPNe); 48 were imaged in our SNAPshot imaging program. We found compact, but non-stellar, morphologies in about a quarter of our observed sample. The remaining objects are either unresolved, or only marginally resolved. Aspherical structure is seen in the resolved objects. The aspherical structure in nPPNe is different from that observed in PPNe, which generally show limb-brightened, roughly equal-sized lobes on both sides of the center. In contrast, only one-sided structures are seen in our survey nPPNe. In some objects, a diffuse, round, halo is also seen, representing the undisturbed AGB mass-loss envelope. A few sources show discrete circular (partial) arc-like features. The discovery of the one-side collimated features, together with detailed earlier studies of a few nPPNe (e.g. V Hya, IRC+10216), supports the hypothesis that the mechanism for creating the large-scale density inhomogeneties are high velocity outflows carving the AGB mass-loss envelope from the inside out.

  12. On the nature of the most obscured C-rich AGB stars in the Magellanic Clouds

    NASA Astrophysics Data System (ADS)

    Ventura, P.; Karakas, A. I.; Dell'Agli, F.; García-Hernández, D. A.; Boyer, M. L.; Di Criscienzo, M.

    2016-04-01

    The stars in the Magellanic Clouds with the largest degree of obscuration are used to probe the highly uncertain physics of stars in the asymptotic giant branch (AGB) phase of evolution. Carbon stars in particular provide key information on the amount of third dredge-up and mass-loss. We use two independent stellar evolution codes to test how a different treatment of the physics affects the evolution on the AGB. The output from the two codes is used to determine the rates of dust formation in the circumstellar envelope, where the method used to determine the dust is the same for each case. The stars with the largest degree of obscuration in the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) are identified as the progeny of objects of initial mass 2.5-3 M⊙ and ˜1.5 M⊙, respectively. This difference in mass is motivated by the difference in the star formation histories of the two galaxies, and offers a simple explanation of the redder infrared colours of C-stars in the LMC compared to their counterparts in the SMC. The comparison with the Spitzer colours of C-rich AGB stars in the SMC shows that a minimum surface carbon mass fraction X(C) ˜ 5 × 10-3 must have been reached by stars of initial mass around 1.5 M⊙. Our results confirm the necessity of adopting low-temperature opacities in stellar evolutionary models of AGB stars. These opacities allow the stars to obtain mass-loss rates high enough (≳10-4 M⊙ yr-1) to produce the amount of dust needed to reproduce the Spitzer colours.

  13. AGB stars and presolar grains

    SciTech Connect

    Busso, M.; Trippella, O.; Maiorca, E.; Palmerini, S.

    2014-05-09

    Among presolar materials recovered in meteorites, abundant SiC and Al{sub 2}O{sub 3} grains of AGB origins were found. They showed records of C, N, O, {sup 26}Al and s-element isotopic ratios that proved invaluable in constraining the nucleosynthesis models for AGB stars [1, 2]. In particular, when these ratios are measured in SiC grains, they clearly reveal their prevalent origin in cool AGB circumstellar envelopes and provide information on both the local physics and the conditions at the nucleosynthesis site (the H- and He-burning layers deep inside the structure). Among the properties ascertained for the main part of the SiC data (the so-called mainstream ones), we mention a large range of {sup 14}N/{sup 15}N ratios, extending below the solar value [3], and {sup 12}C/{sup 13}C ratios ≳ 30. Other classes of grains, instead, display low carbon isotopic ratios (≳ 10) and a huge dispersion for N isotopes, with cases of large {sup 15}N excess. In the same grains, isotopes currently feeded by slow neutron captures reveal the characteristic pattern expected from this process at an efficiency slightly lower than necessary to explain the solar main s-process component. Complementary constraints can be found in oxide grains, especially Al{sub 2}O{sub 3} crystals. Here, the oxygen isotopes and the content in {sup 26}Al are of a special importance for clarifying the partial mixing processes that are known to affect evolved low-mass stars. Successes in modeling the data, as well as problems in explaining some of the mentioned isotopic ratios through current nucleosynthesis models are briefly outlined.

  14. X-ray Observations of AGB Stars with XMM-Newton

    NASA Astrophysics Data System (ADS)

    Kastner, J. H.; Soker, N.

    2003-12-01

    We report the preliminary results of an XMM-Newton observing program to determine the X-ray emission properties of a sample of well-studied AGB stars. Our goal is to set constraints on magnetic (dynamo) activity during mass-losing AGB evolutionary stages, and thereby test models wherein AGB star magnetic fields influence mass loss geometry and shape planetary nebulae. We detected X-ray emission from the Mira system, with a total EPIC count rate of ˜0.11 s-1. This emission may be due to accretion or magnetic activity associated with Mira B, a companion of uncertain nature located only 0.6" from the mass-losing AGB star. The X-ray spectrum of the Mira system displays emission from highly ionized Ne, and initial (single-component) spectral fits suggest a characteristic emission region temperature ˜10 MK, intervening absorbing column ˜3×1021 cm-2, and an intrinsic X-ray luminosity of ˜2×1029 ergs s-1. The (apparently single) star T Cas is undetected in X-rays. At the meeting, we will also report on results from observations of TX Cam, an AGB star for which the presence of relatively strong (5-10 G at ˜3 R⋆ ) magnetic fields has been inferred from maser polarization measurements in the radio. This research is partly supported via NASA/GSFC grant NAG5--13158 (XMM-Newton Guest Observer program) to the Center for Imaging Science at Rochester Institute of Technology.

  15. Pulsation, Mass Loss and the Upper Mass Limit

    NASA Astrophysics Data System (ADS)

    Klapp, J.; Corona-Galindo, M. G.

    1990-11-01

    RESUMEN. La existencia de estrellas con masas en exceso de 100 M0 ha sido cuestionada por mucho tiempo. Lfmites superiores para la masa de 100 M0 han sido obtenidos de teorfas de pulsaci6n y formaci6n estelar. En este trabajo nosotros primero investigamos la estabilidad radial de estrellas masivas utilizando la aproximaci6n clasica cuasiadiabatica de Ledoux, la aproximaci6n cuasiadiabatica de Castor y un calculo completamente no-adiabatico. Hemos encontrado que los tres metodos de calculo dan resultados similares siempre y cuando una pequefia regi6n de las capas externas de la estrella sea despreciada para la aproximaci6n clasica. La masa crftica para estabilidad de estrellas masivas ha sido encontrada en acuerdo a trabajos anteriores. Explicamos Ia discrepancia entre este y trabajos anteriores por uno de los autores. Discunmos calculos no-lineales y perdida de masa con respecto a) lfmite superior de masa. The existence of stars with masses in excess of 100 M0 has been questioned for a very long time. Upper mass limits of 100 Me have been obtained from pulsation and star formation theories. In this work we first investigate the radial stability of massive stars using the classical Ledoux's quasiadiabatic approximation. the Castor quasiadiabatic approximation and a fully nonadiabatic calculation. We have found that the three methods of calculation give similar results provided that a small region in outer layers of the star be neglected for the classical approximation. The critical mass for stability of massive stars is found to be in agreement with previous work. We explain the reason for the discrepancy between this and previous work by one of the authors. We discuss non-linear calculations and mass loss with regard to the upper mass limit. Key words: STARS-MASS FUNCTION - STARS-MASS LOSS - STARS-PULSATION

  16. The production of low mass carbon stars - Carbon-rich dredge up or oxygen-rich mass loss?

    NASA Technical Reports Server (NTRS)

    Stencel, R. E.; Pesce, J. E.; Macgregor, K. M.

    1989-01-01

    Conventional theory explains the origin of carbon stars as due to dredge up of carbon enriched material from the stellar core during helium flash events late in the life of solar mass AGB stars. This relatively efficient process, however, seems to produce a larger C/O ratio than observed (Lambert et al., 1987). A secondary effect which could contribute to the appearance of carbon stars, is the selective removal of oxygen from the atmosphere by radiative force expulsion of oxygen-rich dust grains. Calculations for this scenario are presented, which evaluate the degree of momentum coupling between the grains and gas under the thermodynamical conditions of AGB star atmospheres.

  17. Detecting Mass Loss in Main Belt Asteroids

    NASA Astrophysics Data System (ADS)

    Sandberg, Erik; Rajagopal, Jayadev; Ridgway, Susan E.; Kotulla, Ralf C.; Valdes, Francisco; Allen, Lori

    2016-01-01

    Sandberg, E., Rajagopal, J., Ridgway, S.E, Kotulla, R., Valdes, F., Allen, L.The Dark Energy Camera (DECam) on the 4m Blanco telescope at the Cerro Tololo Inter-American Observatory (CTIO) is being used for a survey of Near Earth Objects (NEOs). Here we attempt to identify mass loss in main belt asteroids (MBAs) from these data. A primary motivation is to understand the role that asteroids may play in supplying dust and gas for debris disks. This work focuses on finding methods to automatically pick out asteroids that have qualities indicating possible mass loss. Two methods were chosen: looking for flux above a certain threshold in the asteroid's radial profile, and comparing its PSF to that of a point source. After sifting through 490 asteroids, several have passed these tests and should be followed up with a more rigorous analysis.Sandberg was supported by the NOAO/KPNO Research Experience for Undergraduates (REU) Program which is funded by the National Science Foundation Research Experiences for Undergraduates Program (AST-1262829)

  18. Chemical pollution from AGB Stars

    NASA Astrophysics Data System (ADS)

    Cristallo, S.; Straniero, O.; Gallino, R.; Piersanti, L.; Dominguez, I.

    Low mass AGB Stars are the main contributors to the Galactic s-process enrichment. We present new theoretical results obtained by adopting a full network from H to Bi coupled with the physical evolution of the stellar structure. We describe the formation of a 13C pocket as a consequence of H diffusion from the envelope into the He-rich intershell. Such 13C is burnt during the interpulse phase and provides the main neutron source in these stars. We computed two models with the same total mass (that is 2 M⊙) but two different initial chemical composition, namely (Y=0.269 - Z=0.015) and (Y=0.245 - Z=0.0001), representative of disk and halo stars respectively. We evaluate the differences in the final s-process surface composition and compare the results with the available observational data.

  19. Clouds enhance Greenland ice sheet mass loss

    NASA Astrophysics Data System (ADS)

    Van Tricht, Kristof; Gorodetskaya, Irina V.; L'Ecuyer, Tristan; Lenaerts, Jan T. M.; Lhermitte, Stef; Noel, Brice; Turner, David D.; van den Broeke, Michiel R.; van Lipzig, Nicole P. M.

    2015-04-01

    Clouds have a profound influence on both the Arctic and global climate, while they still represent one of the key uncertainties in climate models, limiting the fidelity of future climate projections. The potentially important role of thin liquid-containing clouds over Greenland in enhancing ice sheet melt has recently gained interest, yet current research is spatially and temporally limited, focusing on particular events, and their large scale impact on the surface mass balance remains unknown. We used a combination of satellite remote sensing (CloudSat - CALIPSO), ground-based observations and climate model (RACMO) data to show that liquid-containing clouds warm the Greenland ice sheet 94% of the time. High surface reflectivity (albedo) for shortwave radiation reduces the cloud shortwave cooling effect on the absorbed fluxes, while not influencing the absorption of longwave radiation. Cloud warming over the ice sheet therefore dominates year-round. Only when albedo values drop below ~0.6 in the coastal areas during summer, the cooling effect starts to overcome the warming effect. The year-round excess of energy due to the presence of liquid-containing clouds has an extensive influence on the mass balance of the ice sheet. Simulations using the SNOWPACK snow model showed not only a strong influence of these liquid-containing clouds on melt increase, but also on the increased sublimation mass loss. Simulations with the Community Earth System Climate Model for the end of the 21st century (2080-2099) show that Greenland clouds contain more liquid water path and less ice water path. This implies that cloud radiative forcing will be further enhanced in the future. Our results therefore urge the need for improving cloud microphysics in climate models, to improve future projections of ice sheet mass balance and global sea level rise.

  20. Mass loss from interacting close binary systems

    NASA Technical Reports Server (NTRS)

    Plavec, M. J.

    1981-01-01

    The three well-defined classes of evolved binary systems that show evidence of present and/or past mass loss are the cataclysmic variables, the Algols, and Wolf-Rayet stars. It is thought that the transformation of supergiant binary systems into the very short-period cataclysmic variables must have been a complex process. The new evidence that has recently been obtained from the far ultraviolet spectra that a certain subclass of the Algols (the Serpentids) are undergoing fairly rapid evolution is discussed. It is thought probable that the remarkable mass outflow observed in them is connected with a strong wind powered by accretion. The origin of the circumbinary clouds or flat disks that probably surround many strongly interacting binaries is not clear. Attention is also given to binary systems with hot white dwarf or subdwarf components, such as the symbiotic objects and the BQ stars; it is noted that in them both components may be prone to an enhanced stellar wind.

  1. Winds, Bubbles, ...but Magnetized: Solutions for High Speed Post-AGB Winds and Their Extreme Collimation

    NASA Astrophysics Data System (ADS)

    García-Segura, G.; López, J. A.; Franco, J.

    2003-01-01

    This paper provides solutions for the origin of post-AGB winds, their acceleration up to high speed, and the subsequent formation of extremely collimated proto-planetary nebulae. Several wind models with terminal velocities from a few tens of km/s up to 10^3km/s are calculated, which produce proto-planetary nebulae with linear momenta in the range 10^36 to 10^40gcm/s and with kinetic energies in the range 10^42 to 10^47 erg. These results match available observations of proto-planetary nebulae. In the present simplistic scheme, the driver of the wind is just the magnetic pressure at the stellar surface. Other forces are not taken into account in this study, except gravity. We conclude that mass-loss rates of post-AGB stars and transition times from late AGB up to planetary nebula central stars could be directly linked with the production of magnetic field at the stellar core. As an example, mass-loss rates as large as 8×10^-5 M[ sun ]/yr and transition times as short as 5000 years are predicted.

  2. Molecular shells in IRC+10216: tracing the mass loss history⋆,⋆⋆,⋆⋆⋆

    PubMed Central

    Cernicharo, J.; Marcelino, N.; Agúndez, M.; Guélin, M.

    2015-01-01

    Thermally-pulsating AGB stars provide three-fourths of the matter returned to the interstellar medium. The mass and chemical composition of their ejecta largely control the chemical evolution of galaxies. Yet, both the mass loss process and the gas chemical composition remain poorly understood. We present maps of the extended 12CO and 13CO emissions in IRC+10216, the envelope of CW Leo, the high mass loss star the closest to the Sun. IRC+10216 is nearly spherical and expands radially with a velocity of 14.5 km s−1. The observations were made On-the-Fly with the IRAM 30 m telescope; their sensibility, calibration, and angular resolution are far higher than all previous studies. The telescope resolution at λ = 1.3 mm (11″ HPBW) corresponds to an expansion time of 500 yr. The CO emission consists of a centrally peaked pedestal and a series of bright, nearly spherical shells. It peaks on CW Leo and remains relatively strong up to rphot = 180″. Further out the emission becomes very weak and vanishes as CO gets photodissociated. As CO is the best tracer of the gas up to rphot, the maps show the mass loss history in the last 8000 yr. The bright CO shells denote over-dense regions. They show that the mass loss process is highly variable on timescales of hundreds of years. The new data, however, do not support previous claims of a strong decrease of the average mass loss in the last few thousand years. The over-dense shells are not perfectly concentric and extend farther to the N-NW. The typical shell separation is 800–1000 yr in the middle of the envelope, but seems to increase outwards. The shell-intershell brightness contrast is ≥3. All those key features can be accounted for if CW Leo has a companion star with a period ≃800 yr that increases the mass loss rate when it comes close to periastron. Higher angular resolution observations are needed to fully resolve the dense shells and measure the density contrast. The latter plays an essential role in our

  3. Mass loss in 2D rotating stellar models

    SciTech Connect

    Lovekin, Caterine; Deupree, Bob

    2010-10-05

    Radiatively driven mass loss is an important factor in the evolution of massive stars . The mass loss rates depend on a number of stellar parameters, including the effective temperature and luminosity. Massive stars are also often rapidly rotating, which affects their structure and evolution. In sufficiently rapidly rotating stars, both the effective temperature and radius vary significantly as a function of latitude, and hence mass loss rates can vary appreciably between the poles and the equator. In this work, we discuss the addition of mass loss to a 2D stellar evolution code (ROTORC) and compare evolution sequences with and without mass loss. Preliminary results indicate that a full 2D calculation of mass loss using the local effective temperature and luminosity can significantly affect the distribution of mass loss in rotating main sequence stars. More mass is lost from the pole than predicted by 1D models, while less mass is lost at the equator. This change in the distribution of mass loss will affect the angular momentum loss, the surface temperature and luminosity, and even the interior structure of the star. After a single mass loss event, these effects are small, but can be expected to accumulate over the course of the main sequence evolution.

  4. Mass loss from red giants - Infrared spectroscopy

    NASA Technical Reports Server (NTRS)

    Wannier, P. G.

    1985-01-01

    A discussion is presented of IR spectroscopy, particularly high-resolution spectroscopy in the approximately 1-20 micron band, as it impacts the study of circumstellar envelopes. The molecular bands within this region contain an enormous amount of information, especially when observed with sufficient resolution to obtain kinematic information. In a single spectrum, it is possible to resolve lines from up to 50 different rotational/vibrational levels of a given molecule and to detect several different isotopic variants. When high resolution techniques are combined with mapping techniques and/or time sequence observations of variable stars, the resulting information can paint a very detailed picture of the mass-loss phenomenon. To date, near-IR observations have been made of 20 molecular species. CO is the most widely observed molecule and useful information has been gleaned from the observed rotational excitation, kinematics, time variability and spatial structure of its lines. Examples of different observing techniques are discussed in the following sections.

  5. Mass loss from the atmosphere of Pluto

    NASA Astrophysics Data System (ADS)

    Liang, Mao-Chang; Yen, Chien-Chang; Taam, Ronald

    2015-11-01

    Molecules can escape readily from the atmosphere of Pluto. Hydrodynamic escape is a process that drives large scale escape. The process was generally believed to produce rather small isotopic fractionation. Here, we show that the escape highly fractionates the isotopic composition of nitrogen. The process preferentially selects lighter species, with an escape probability ~30% higher for the lighter isotopologue. This fractionation factor is higher than the fractionations occurring in most of known processes in modifying the distributions of molecules in the planetary atmospheres. The validity of the model can be tested against the upcoming data, mainly nitrogen abundance in the outer atmosphere of Pluto, from the New Horizons. The property of the selection can significantly modify the isotopic composition of the atmosphere, leaving the present-day atmosphere isotopically heavier than the ancient one. This also impacts the current view of the evolution of planetary atmospheres. Venus, for example, may not need that much mass loss, in order to explain the current D/H ratio.

  6. A new tool for post-AGB SED classification

    NASA Astrophysics Data System (ADS)

    Bendjoya, P.; Suarez, O.; Galluccio, L.; Michel, O.

    We present the results of an unsupervised classification method applied on a set of 344 spectral energy distributions (SED) of post-AGB stars extracted from the Torun catalogue of Galactic post-AGB stars. This method aims to find a new unbiased method for post-AGB star classification based on the information contained in the IR region of the SED (fluxes, IR excess, colours). We used the data from IRAS and MSX satellites, and from the 2MASS survey. We applied a classification method based on the construction of the dataset of a minimal spanning tree (MST) with the Prim's algorithm. In order to build this tree, different metrics have been tested on both flux and color indices. Our method is able to classify the set of 344 post-AGB stars in 9 distinct groups according to their SEDs.

  7. Fast Winds and Mass Loss from Metal-Poor Field Giants

    NASA Astrophysics Data System (ADS)

    Dupree, A. K.; Smith, Graeme H.; Strader, Jay

    2009-11-01

    Echelle spectra of the infrared He I λ10830 line were obtained with NIRSPEC on the Keck 2 telescope for 41 metal-deficient field giant stars including those on the red giant branch (RGB), asymptotic giant branch (AGB), and red horizontal branch (RHB). The presence of this He I line is ubiquitous in stars with T effgsim 4500 K and MV fainter than -1.5, and reveals the dynamics of the atmosphere. The line strength increases with effective temperature for T effgsim 5300 K in RHB stars. In AGB and RGB stars, the line strength increases with luminosity. Fast outflows (gsim 60 km s-1) are detected from the majority of the stars and about 40% of the outflows have sufficient speed as to allow escape of material from the star as well as from a globular cluster. Outflow speeds and line strengths do not depend on metallicity for our sample ([Fe/H]= -0.7 to -3.0), suggesting the driving mechanism for these winds derives from magnetic and/or hydrodynamic processes. Gas outflows are present in every luminous giant, but are not detected in all stars of lower luminosity indicating possible variability. Mass loss rates ranging from ~3 × 10-10 to ~6 × 10-8 M sun yr-1 estimated from the Sobolev approximation for line formation represent values with evolutionary significance for red giants and RHB stars. We estimate that 0.2 M sun will be lost on the RGB, and the torque of this wind can account for observations of slowly rotating RHB stars in the field. About 0.1-0.2 M sun will be lost on the RHB itself. This first empirical determination of mass loss on the RHB may contribute to the appearance of extended horizontal branches in globular clusters. The spectra appear to resolve the problem of missing intracluster material in globular clusters. Opportunities exist for "wind smothering" of dwarf stars by winds from the evolved population, possibly leading to surface pollution in regions of high stellar density. Data presented herein were obtained at the W. M. Keck Observatory, which

  8. Post-AGB stars in the Magellanic Clouds and neutron-capture processes in AGB stars

    NASA Astrophysics Data System (ADS)

    Lugaro, M.; Campbell, S. W.; Van Winckel, H.; De Smedt, K.; Karakas, A. I.; Käppeler, F.

    2015-11-01

    Aims: We explore modifications to the current scenario for the slow neutron-capture process (the s-process) in asymptotic giant branch (AGB) stars to account for the Pb deficiency observed in post-AGB stars of low metallicity ([Fe/H] ≃-1.2) and low initial mass (≃ 1-1.5 M⊙) in the Large and Small Magellanic Clouds. Methods: We calculated the stellar evolution and nucleosynthesis for a 1.3 M⊙ star with [Fe/H] = -1.3 and tested different amounts and distributions of protons leading to the production of the main neutron source within the 13C-pocket and proton ingestion scenarios. Results: No s-process models can fully reproduce the abundance patterns observed in the post-AGB stars. When the Pb production is lowered, the abundances of the elements between Eu and Pb, such as Er, Yb, W, and Hf, are also lowered to below those observed. Conclusions: Neutron-capture processes with neutron densities intermediate between the s and the rapid neutron-capture processes may provide a solution to this problem and be a common occurrence in low-mass, low-metallicity AGB stars.

  9. Post-AGB Stars in the AKARI Survey

    NASA Astrophysics Data System (ADS)

    Siódmiak, N.; Cox, N.; Szczerba, R.; García-Lario, P.

    2009-12-01

    Obscured by their circumstellar dusty envelopes post-AGB stars emit a large fraction of their energy in the infrared and thus, infrared sky surveys like IRAS were essential for discoveries of post-AGBs in the past. Now, with the AKARI infrared sky survey we can extend our knowledge about the late stages of stellar evolution. The long-term goal of our work is to define new photometric criteria to distinguish new post-AGB candidates from the AKARI data. We have cross-correlated the Toruń catalogue of Galactic post-AGB and related objects with the AKARI/FIS All-Sky Survey Bright Source Catalogue (for simplicity, hereafter AKARI). The scientific and technical aspects of our work are presented here as well as our plans for the future. In particular, we found that only 9 post-AGB sources were detected in all four AKARI bands. The most famous objects like: Red Rectangle, Egg Nebula, Minkowski’s Footprint belong to this group. From the technical point of view we discuss positional accuracy by comparing (mostly) 2MASS coordinates of post-AGB objects with those given by AKARI; flux reliability by comparing IRAS 60 and 100 μm fluxes with those from AKARI -N65 and AKARI -90 bands, respectively; as well as completeness of the sample as a function of the IRAS fluxes.

  10. Early solar mass loss, element diffusion, and solar oscillation frequencies

    SciTech Connect

    Guzik, J.A.; Cox, A.N.

    1994-07-01

    Swenson and Faulkner, and Boothroyd et al. investigated the possibility that early main-sequence mass loss via a stronger early solar wind could be responsible for the observed solar lithium and beryllium depiction. This depletion requires a total mass loss of {approximately}0.1 M{circle_dot}, nearly independent of the mass loss timescale. We have calculated the evolution and oscillation frequencies of solar models including helium and element diffusion, and such early solar mass loss. We show that extreme mass loss of 1 M{circle_dot} is easily ruled out by the low-degree p-modes that probe the solar center and sense the steeper molecular weight gradient produced by the early phase of more rapid hydrogen burning. The effects on central structure are much smaller for models with an initial mass of 1.1 M{circle_dot} and exponentially-decreasing mass loss irate with e-folding timescale 0.45 Gyr. While such mass loss slightly worsens the agreement between observed and calculated low-degree modes, the observational uncertainties of several tenths of a microhertz weaken this conclusion. Surprisingly, the intermediate-degree modes with much smaller observational uncertainties that probe the convection zone bottom prove to be the key to discriminating between models: The early mass loss phase decreases the total amount of helium and heavier elements diffused from the convection zone, and the extent of the diffusion produced composition gradient just below the convection zone, deteriorating the agreement with observed frequencies for these modes. Thus it appears that oscillations can also rule out this smaller amount of gradual early main-sequence mass loss in the young Sun. The mass loss phase must be confined to substantially under a billion years, probably 0.5 Gyr or less, to simultaneously solve the solar Li/Be problem and avoid discrepancies with solar oscillation frequencies.

  11. Mass loss upper limits for A and F dwarfs

    NASA Technical Reports Server (NTRS)

    Brown, A.; Veale, A.; Judge, P.; Bookbinder, J.; Hubeny, I.

    1990-01-01

    The upper limits of the ionized mass losses of A- and F-type main sequence stars are obtained with the VLA to investigate the theory that pulsationally driven winds contribute to substantial mass loss in the stars. The upper limits are found to be at least one order of magnitude lower than the mass-loss loci proposed by Willson et al. (1987). Because any wind flowing from the stars should be detectable, the notion that A dwarfs are evolving into G dwarfs cannot be supported by the amount of mass that A and F dwarfs are shown to be losing.

  12. Mass loss parameters for typical Shuttle materials

    NASA Technical Reports Server (NTRS)

    Muscari, J. A.; Odonnell, T.

    1982-01-01

    The weight loss of twenty different typical Shuttle materials was measured with a thermogravimetric analyzer as the material temperature was increased from ambient to 300 C. An additional ten tests were performed where conditioning of the material varied. The materials were selected from each general grouping such as adhesives, coatings, lubricants, encapsulants, elastomers, and resins. Care was taken in the preparation, curing, and preconditioning of the materials to simulate flight use. Making the assumption that the weight loss follows first order rate theory, the source outgassing parameters for these thirty materials is presented.

  13. Mass-loss Rate by the Mira in the Symbiotic Binary V1016 Cygni from Raman Scattering

    NASA Astrophysics Data System (ADS)

    Sekeráš, M.; Skopal, A.

    2015-10-01

    The mass-loss rate from Mira variables represents a key parameter in our understanding of their evolutionary tracks. We introduce a method for determining the mass-loss rate from the Mira component in D-type symbiotic binaries via the Raman scattering of atomic hydrogen in the wind from the giant. Using our method, we investigated Raman He ii λ 1025\\to λ 6545 conversion in the spectrum of the symbiotic Mira V1016 Cyg. We determined its efficiency, η = 0.102, 0.148, and the corresponding mass-loss rate, \\dot{M}={2.0}-0.2+0.1× {10}-6, {2.7}-0.1+0.2× {10}-6 {M}⊙ {{{yr}}}-1, using our spectra from 2006 April and 2007 July, respectively. Our values of \\dot{M} that we derived from Raman scattering are comparable with those obtained independently by other methods. Applying the method to other Mira-white dwarf binary systems can provide a necessary constraint in the calculation of asymptotic giant branch (AGB) evolution.

  14. ALMA reveals sunburn: CO dissociation around AGB stars in the globular cluster 47 Tucanae

    NASA Astrophysics Data System (ADS)

    McDonald, I.; Zijlstra, A. A.; Lagadec, E.; Sloan, G. C.; Boyer, M. L.; Matsuura, M.; Smith, R. J.; Smith, C. L.; Yates, J. A.; van Loon, J. Th.; Jones, O. C.; Ramstedt, S.; Avison, A.; Justtanont, K.; Olofsson, H.; Blommaert, J. A. D. L.; Goldman, S. R.; Groenewegen, M. A. T.

    2015-11-01

    Atacama Large Millimetre Array observations show a non-detection of carbon monoxide around the four most luminous asymptotic giant branch (AGB) stars in the globular cluster 47 Tucanae. Stellar evolution models and star counts show that the mass-loss rates from these stars should be ˜1.2-3.5 × 10-7 M⊙ yr-1. We would naïvely expect such stars to be detectable at this distance (4.5 kpc). By modelling the ultraviolet radiation field from post-AGB stars and white dwarfs in 47 Tuc, we conclude that CO should be dissociated abnormally close to the stars. We estimate that the CO envelopes will be truncated at a few hundred stellar radii from their host stars and that the line intensities are about two orders of magnitude below our current detection limits. The truncation of CO envelopes should be important for AGB stars in dense clusters. Observing the CO (3-2) and higher transitions and targeting stars far from the centres of clusters should result in the detections needed to measure the outflow velocities from these stars.

  15. FUEL EFFICIENT GALAXIES: SUSTAINING STAR FORMATION WITH STELLAR MASS LOSS

    SciTech Connect

    Leitner, Samuel N.; Kravtsov, Andrey V.

    2011-06-10

    We examine the importance of secular stellar mass loss for fueling ongoing star formation in disk galaxies during the late stages of their evolution. For a galaxy of a given stellar mass, we calculate the total mass loss rate of its entire stellar population using star formation histories derived from the observed evolution of the M{sub *}-star formation rate (SFR) relation, along with the predictions of standard stellar evolution models for stellar mass loss for a variety of initial stellar mass functions. Our model shows that recycled gas from stellar mass loss can provide most or all of the fuel required to sustain the current level of star formation in late-type galaxies. Stellar mass loss can therefore remove the tension between the low gas infall rates that are derived from observations and the relatively rapid star formation occurring in disk galaxies. For galaxies where cold gas infall rates have been estimated, we demonstrate explicitly that stellar mass loss can account for most of the deficit between their SFR and infall rate.

  16. Surprising detection of an equatorial dust lane on the AGB star IRC+10216

    NASA Astrophysics Data System (ADS)

    Jeffers, S. V.; Min, M.; Waters, L. B. F. M.; Canovas, H.; Pols, O. R.; Rodenhuis, M.; de Juan Ovelar, M.; Keller, C. U.; Decin, L.

    2014-12-01

    Aims: Understanding the formation of planetary nebulae remains elusive because in the preceding asymptotic giant branch (AGB) phase these stars are heavily enshrouded in an optically thick dusty envelope. Methods: To further understand the morphology of the circumstellar environments of AGB stars we observe the closest carbon-rich AGB star IRC+10216 in scattered light. Results: When imaged in scattered light at optical wavelengths, IRC+10216 surprisingly shows a narrow equatorial density enhancement, in contrast to the large-scale spherical rings that have been imaged much further out. We use radiative transfer models to interpret this structure in terms of two models: firstly, an equatorial density enhancement, commonly observed in the more evolved post-AGB stars, and secondly, in terms of a dust rings model, where a local enhancement of mass-loss creates a spiral ring as the star rotates. Conclusions: We conclude that both models can be used to reproduce the dark lane in the scattered light images, which is caused by an equatorially density enhancement formed by dense dust rather than a bipolar outflow as previously thought. We are unable to place constraints on the formation of the equatorial density enhancement by a binary system. Final reduced images (FITS) are available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/572/A3Based on observations made with 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 Astrofísica de Canarias.

  17. Transitory O-rich chemistry in heavily obscured C-rich post-AGB stars

    NASA Astrophysics Data System (ADS)

    García-Hernández, D. A.; García-Lario, P.; Cernicharo, J.; Engels, D.; Perea-Calderón, J. V.

    2016-07-01

    Spitzer/IRS spectra of eleven heavily obscured C-rich sources rapidly evolving from asymptotic giant branch (AGB) stars to Planetary Nebulae are presented. IRAM 30m observations for three of these post-AGBs are also reported. A few (3) of these sources are known to exhibit strongly variable maser emission of O-bearing molecules such as OH and H2 O, suggesting a transitory O-rich chemistry because of the quickly changing physical and chemical conditions in this short evolutionary phase. Interestingly, the Spitzer/IRS spectra show a rich circumstellar carbon chemistry, as revealed by the detection of small hydrocarbon molecules such as C2H2, C4H2, C6H2, C6H6, and HCN. Benzene is detected towards two sources, bringing up to three the total number of Galactic post-AGBs where this molecule has been detected. In addition, we report evidence for the possible detection of other hydrocarbon molecules like HC3N, CH3C2H, and CH3 in several of these sources. The available IRAM 30m data confirm that the central stars are C-rich - in despite of the presence of O-rich masers - and the presence of high velocity molecular outflows together with extreme AGB mass-loss rates (∼⃒10-4 Mʘ /yr). Our observations confirm the polymerization model of Cernicharo [1] that predicts a rich photochemistry in the neutral regions of these objects on timescales shorter than the dynamical evolution of the central HII region, leading to the formation of small C-rich molecules and a transitory O-rich chemistry.

  18. Mapping Greenland's mass loss in space and time.

    PubMed

    Harig, Christopher; Simons, Frederik J

    2012-12-01

    The melting of polar ice sheets is a major contributor to global sea-level rise. Early estimates of the mass lost from the Greenland ice cap, based on satellite gravity data collected by the Gravity Recovery and Climate Experiment, have widely varied. Although the continentally and decadally averaged estimated trends have now more or less converged, to this date, there has been little clarity on the detailed spatial distribution of Greenland's mass loss and how the geographical pattern has varied on relatively shorter time scales. Here, we present a spatially and temporally resolved estimation of the ice mass change over Greenland between April of 2002 and August of 2011. Although the total mass loss trend has remained linear, actively changing areas of mass loss were concentrated on the southeastern and northwestern coasts, with ice mass in the center of Greenland steadily increasing over the decade. PMID:23169646

  19. Mass loss and OH maser emission from Mira variables

    NASA Technical Reports Server (NTRS)

    Michalitsianos, A. G.; Kafatos, M.

    1978-01-01

    The mass, radius, and luminosity of 26 Mira variables that are known OH sources of radio emission at 1612 MHz have been estimated. The time-independent solution of Salpeter's (1974) stellar-wind equation and a period-density relation are used to solve for basic stellar parameters, with the aid of the terminal expansion velocity of the OH maser cloud. Masses obtained from these calculations are consistent with other estimated values for masses of Mira variables. Good agreement is obtained when comparing the rate of mass loss as determined from Reimers's (1977) semiempirical relation with estimates of the mass-loss rate as deduced from theoretical models involving radiation pressure on grains. These calculations suggest a strong correlation between the mass-loss rate and the pulsation period. Arguments concerning the general properties of silicate grains from radiation-pressure-driven stellar-wind equations are discussed.

  20. Mapping Greenland’s mass loss in space and time

    PubMed Central

    Harig, Christopher; Simons, Frederik J.

    2012-01-01

    The melting of polar ice sheets is a major contributor to global sea-level rise. Early estimates of the mass lost from the Greenland ice cap, based on satellite gravity data collected by the Gravity Recovery and Climate Experiment, have widely varied. Although the continentally and decadally averaged estimated trends have now more or less converged, to this date, there has been little clarity on the detailed spatial distribution of Greenland’s mass loss and how the geographical pattern has varied on relatively shorter time scales. Here, we present a spatially and temporally resolved estimation of the ice mass change over Greenland between April of 2002 and August of 2011. Although the total mass loss trend has remained linear, actively changing areas of mass loss were concentrated on the southeastern and northwestern coasts, with ice mass in the center of Greenland steadily increasing over the decade. PMID:23169646

  1. AGB yields and Galactic Chemical Evolution: last updated

    NASA Astrophysics Data System (ADS)

    Bisterzo, S.; Travaglio, C.; Wiescher, M.; Gallino, R.; Köppeler, F.; Straniero, O.; Cristallo, S.; Imbriani, G.; Görres, J.; deBoer, R. J.

    2016-01-01

    We study the s-process abundances at the epoch of the Solar-system formation as the outcome of nucleosynthesis occurring in AGB stars of various masses and metallicities. The calculations have been performed with the Galactic chemical evolution (GCE) model presented by [1, 2]. With respect to previous works, we used updated solar meteoritic abundances, a neutron capture cross section network that includes the most recent measurements, and we implemented the s-process yields with an extended range of AGB initial masses. The new set of AGB yields includes a new evaluation of the 22Ne(α, n)25Mg rate, which takes into account the most recent experimental information.

  2. Chemistry and distribution of daughter species in the circumstellar envelopes of O-rich AGB stars

    NASA Astrophysics Data System (ADS)

    Li, Xiaohu; Millar, Tom J.; Heays, Alan N.; Walsh, Catherine; van Dishoeck, Ewine F.; Cherchneff, Isabelle

    2016-03-01

    Context. Thanks to the advent of Herschel and ALMA, new high-quality observations of molecules present in the circumstellar envelopes of asymptotic giant branch (AGB) stars are being reported that reveal large differences from the existing chemical models. New molecular data and more comprehensive models of the chemistry in circumstellar envelopes are now available. Aims: The aims are to determine and study the important formation and destruction pathways in the envelopes of O-rich AGB stars and to provide more reliable predictions of abundances, column densities, and radial distributions for potentially detectable species with physical conditions applicable to the envelope surrounding IK Tau. Methods: We use a large gas-phase chemical model of an AGB envelope including the effects of CO and N2 self-shielding in a spherical geometry and a newly compiled list of inner-circumstellar envelope parent species derived from detailed modeling and observations. We trace the dominant chemistry in the expanding envelope and investigate the chemistry as a probe for the physics of the AGB phase by studying variations of abundances with mass-loss rates and expansion velocities. Results: We find a pattern of daughter molecules forming from the photodissociation products of parent species with contributions from ion-neutral abstraction and dissociative recombination. The chemistry in the outer zones differs from that in traditional PDRs in that photoionization of daughter species plays a significant role. With the proper treatment of self-shielding, the N → N2 and C+→ CO transitions are shifted outward by factors of 7 and 2, respectively, compared with earlier models. An upper limit on the abundance of CH4 as a parent species of (≲2.5 × 10-6 with respect to H2) is found for IK Tau, and several potentially observable molecules with relatively simple chemical links to other parent species are determined. The assumed stellar mass-loss rate, in particular, has an impact on the

  3. Herschel and ALMA observations of AGB star envelopes

    NASA Astrophysics Data System (ADS)

    Katrien Els Decin, Leen

    2015-08-01

    The stellar winds of evolved (super)giant stars are known to be the prime birthplaces for the interstellar material in our galaxy. Fusion in the stellar interiors creates carbon, nitrogen, oxygen, and for more massive stars elements such as magnesium, sulphur etc. are synthesized. Thanks to dredge-ups in the stellar atmosphere and subsequent extensive mass loss through a stellar wind this material is injected into the interstellar medium (ISM).These stellar winds are really unique chemical laboratories in which various gas-phase and gas-dust processes create and destroy gas and dust species and hence manufacture the pristine building blocks of the ISM. The efficiency and working of these various chemical processes is ultimately linked to the dynamical processes which establish the morpho-kinematical structure of the wind. Unraveling the intriguing coupling between these macro-scale dynamical and micro-scale chemical processes is a real challenge to which recent advances in instrumentation, theoretical modeling, and laboratory experiments have contributed a lot. Thanks to their unprecedented sensitivity, spatial resolution and wavelength coverage, Herschel and ALMA have proven to be two key instruments in solving some enigmas related to AGB stellar winds. In this talk, I will give a review of some of the most recent results in the field of AGB stellar winds based on Herschel and ALMA data and I will discuss some open questions that I hope will be answered in the next decade thanks to a combined effort between instrumentation and laboratory specialists and theoretical astrophysicists.

  4. New input data for synthetic AGB evolution

    NASA Astrophysics Data System (ADS)

    Wagenhuber, J.; Groenewegen, M. A. T.

    1998-12-01

    Analytic formulae are presented to construct detailed secular lightcurves of both early asymptotic giant branch (AGB) and thermally pulsing AGB stars. They are based on an extensive grid of evolutionary calculations, performed with an updated stellar evolution code. Basic input parameters are the initial mass MI i, 0.8 <= MI i/Msun <= 7, metallicity ZI i =0.0001, 0.008, 0.02, and the mixing length theory (MLT) parameter. The formulae allow for two important effects, namely that the first pulses do not reach the full amplitude, and hot bottom burning (HBB) in massive stars, which are both not accounted for by core mass - luminosity relations of the usual type. Furthermore, the dependence of the effective temperature and a few other quantities characterizing the conditions at the base of the convective envelope, which are relevant for HBB, are investigated as functions of luminosity, total and core mass for different formulations of the convection theory applied, MLT or Canuto & Mazzitelli's (\\cite{can:maz}) theory.

  5. ALMA Observations of Anisotropic Dust Mass Loss around VY CMa

    NASA Astrophysics Data System (ADS)

    O'Gorman, E.; Vlemmings, W.; Richards, A. M. S.; Baudry, A.; De Beck, E.; Decin, L.; Harper, G. M.; Humphreys, E. M.; Kervella, P.; Khouri, T.; Muller, S.

    2015-12-01

    We present high resolution ALMA Science Verification data of the continuum emission around the highly evolved oxygen-rich red supergiant VY CMa. These data enable us to study the dust in its inner circumstellar environment at a spatial resolution of 129 mas at 321 GHz and 59 mas at 658 GHz, thus allowing us to trace dust on spatial scales down to 11 R⋆ (71 AU). Two prominent dust components are detected and resolved. We find that at least 17% of the dust mass around VY CMa is located in clumps ejected within a more quiescent roughly spherical stellar wind, with a quiescent dust mass loss rate of 5×10-6 M⊙ yr-1. The anisotropic morphology of the dust indicates a continuous, directed mass loss over a few decades, suggesting that this mass loss cannot be driven by large convection cells alone.

  6. Secular dynamics in hierarchical three-body systems with mass loss and mass transfer

    SciTech Connect

    Michaely, Erez; Perets, Hagai B.

    2014-10-20

    Recent studies have shown that secular evolution of triple systems can play a major role in the evolution and interaction of their inner binaries. Very few studies explored the stellar evolution of triple systems, and in particular the mass-loss phase of the evolving stellar components. Here we study the dynamical secular evolution of hierarchical triple systems undergoing mass loss. We use the secular evolution equations and include the effects of mass loss and mass transfer, as well as general relativistic effects. We present various evolutionary channels taking place in such evolving triples, and discuss both the effects of mass loss and mass transfer in the inner binary system, as well as the effects of mass loss/transfer from an outer third companion. We discuss several distinct types/regimes of triple secular evolution, where the specific behavior of a triple system can sensitively depend on its hierarchy and the relative importance of classical and general relativistic effects. We show that the orbital changes due to mass-loss and/or mass-transfer processes can effectively transfer a triple system from one dynamical regime to another. In particular, mass loss/transfer can both induce and quench high-amplitude (Lidov-Kozai) variations in the eccentricity and inclination of the inner binaries of evolving triples. They can also change the system dynamics from an orderly periodic behavior to a chaotic one, and vice versa.

  7. Optically visible post-AGB/RGB stars and young stellar objects in the Small Magellanic Cloud: candidate selection, spectral energy distributions and spectroscopic examination

    NASA Astrophysics Data System (ADS)

    Kamath, D.; Wood, P. R.; Van Winckel, H.

    2014-04-01

    we have identified are in good agreement with the stellar evolution models with some mass-loss in the post-AGB phase and a small amount of re-accretion in the lower luminosity post-RGB phase. This study also resulted in a new sample of 40 young stellar objects (YSOs) of A-F spectral type. The 40 YSO candidates for which we could estimate stellar parameters are luminous and of high mass (˜3-10 M⊙). They lie on the cool side of the usually adopted birthline in the HR-diagram. This line separates visually obscured protostars from optically visible pre-main-sequence stars, meaning that our YSO candidates have become optically visible in the region of the HR diagram usually reserved for obscured protostars. Additionally, we also identified a group of 63 objects whose spectra are dominated by emission lines and in some cases, a significant UV continuum. These objects are very likely to be either hot post-AGB/RGB candidates or luminous YSOs.

  8. Lithium formation in massive AGB stars: new models

    NASA Astrophysics Data System (ADS)

    Mazzitelli, I.; D'Antona, F.; Ventura, P.

    We present new AGB models including full coupling of nuclear evolution and turbulent transport in a diffusive scheme (Ventura et al. 1998). The novelty of these computations resides in the use of a Full Spectrum of Turbulence (FST) convective model, which allows to compute not only the appropriate convective flux distribution of billions of eddy scales (opposed to the one-eddy Mixing Length approximation), but also the self consistent average turbulent velocity and convective scale length which enter in the computation of the diffusion coefficient. Thus this new model contains a smaller number of free parameters with respect to previous MLT based computations. The coupled diffusion scheme treats independently 14 elements from ^1H to 18O, and in particular treats the production and destruction of ^7Li in the Hot Bottom Burning phase, which the FST convective models naturally achieve for masses approximately greater than 4.5M_odot (D'Antona and Mazzitelli 1996). The dependence of Lithium production on the evolving stellar mass, on the mass loss rate and on the chemical composition is presented. Predictions are given on the role of this lithium production for the galactic chemical evolution (e.g. D'Antona and Matteucci 1991), and the complete project for the computations is outlined.

  9. Spitzer Light Curves of Dusty AGB Stars in the Small Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Sargent, Benjamin; Meixner, Margaret; Riebel, David; Vijh, Uma; Hora, Joe; Boyer, Martha; Cook, Kem; Groenewegen, Martin; Whitelock, Patricia; Ita, Yoshifusa; Feast, Michael; Kemper, Ciska; Marengo, Massimo; Otsuka, Masaaki; Srinivasan, Sundar

    2014-12-01

    Asymptotic giant branch (AGB) variable stars are, together with supernovae, the main sources of enrichment of the interstellar medium (ISM) in processed material, particularly carbon, nitrogen and heavy s-process elements. The dustiest, extreme AGB stars contribute the largest enrichment per star. We propose to measure the first light curves for 32 of the dustiest AGB variable stars in the Small Magellanic Cloud (SMC) using the warm Spitzer mission's IRAC 3.6 and 4.5 micron imaging for monthly imaging measurements. We know most are variable based on dual-epoch observations from the Spitzer Surveying the Agents of Galaxy Evolution (SAGE) surveys of the SMC and ground-based near-infrared observations, but we have not observed these dusty SMC stars at the mid-infrared wavelengths available to Spitzer. Only Spitzer will be able to measure the light curve of this key phase of the AGB: the dustiest and indeed final stage of the AGB. Without this information, our developing picture of AGB evolution is decidedly incomplete. The observations we propose will test the validity of AGB evolution models, and, thus, their predictions of the return of mass and nucleosynthetic products to the ISM. A value-added component to this study is that we will obtain variability information on other AGB stars that lie within the fields of view of our observations. This proposal continues the studies we have begun with our Cycle 9 program (pid 90219) and our Cycle 10 program (pid 10154).

  10. Detailed modelling of the circumstellar molecular line emission of the S-type AGB star W Aquilae

    NASA Astrophysics Data System (ADS)

    Danilovich, T.; Bergman, P.; Justtanont, K.; Lombaert, R.; Maercker, M.; Olofsson, H.; Ramstedt, S.; Royer, P.

    2014-09-01

    Context. S-type AGB stars have a C/O ratio which suggests that they are transition objects between oxygen-rich M-type stars and carbon-rich C-type stars. As such, their circumstellar compositions of gas and dust are thought to be sensitive to their precise C/O ratio, and it is therefore of particular interest to examine their circumstellar properties. Aims: We present new Herschel HIFI and PACS sub-millimetre and far-infrared line observations of several molecular species towards the S-type AGB star W Aql. We use these observations, which probe a wide range of gas temperatures, to constrain the circumstellar properties of W Aql, including mass-loss rate and molecular abundances. Methods: We used radiative transfer codes to model the circumstellar dust and molecular line emission to determine circumstellar properties and molecular abundances. We assumed a spherically symmetric envelope formed by a constant mass-loss rate driven by an accelerating wind. Our model includes fully integrated H2O line cooling as part of the solution of the energy balance. Results: We detect circumstellar molecular lines from CO, H2O, SiO, HCN, and, for the first time in an S-type AGB star, NH3. The radiative transfer calculations result in an estimated mass-loss rate for W Aql of 4.0 × 10-6 M⊙ yr-1 based on the 12CO lines. The estimated 12CO/13CO ratio is 29, which is in line with ratios previously derived for S-type AGB stars. We find an H2O abundance of 1.5 × 10-5, which is intermediate to the abundances expected for M and C stars, and an ortho/para ratio for H2O that is consistent with formation at warm temperatures. We find an HCN abundance of 3 × 10-6, and, although no CN lines are detected using HIFI, we are able to put some constraints on the abundance, 6 × 10-6, and distribution of CN in W Aql's circumstellar envelopeusing ground-based data. We find an SiO abundance of 3 × 10-6, and an NH3 abundance of 1.7 × 10-5, confined to a small envelope. If we include uncertainties

  11. VizieR Online Data Catalog: Optical spectra of post-AGB stars (Bakker+ 1997)

    NASA Astrophysics Data System (ADS)

    Bakker, E. J.; van Dishoeck, E. F.; Waters, L. B. F. M.; Schoenmaker, T.

    1996-10-01

    We present optical high-resolution spectra of a sample of sixteen post-AGB stars and IRC +10216. Of the post-AGB stars, ten show C2 Phillips (A1{PI}u- X1{SIGMA}+g) and Swan (d3{PI}g-a3{PI}u) and CN Red System (A2{PI}-X2{SIGMA}+) absorption, one CH+ (A1{PI}-X1{SIGMA}+) emission, one CH+ absorption, and four without any molecules. We find typically Trot ~43-399, 155-202, and 18-50K, logN~14.90-15.57, 14.35, and 15.03-16.47cm-2 for C2, CH+, and CN respectively, and 0.6<=N(CN)/N(C2)<=11.2. We did not detect isotopic lines, which places a lower limit on the isotope ratio of 12C/13C>20. The presence of C2 and CN absorption is correlated with cold dust (Tdust<=300K) and the presence of CH+ with hot dust (Tdust>=300K). All objects with the unidentified 21μm emission feature exhibit C2 and CN absorption, but not all objects with C2 and CN detections exhibit a 21μm feature. The derived expansion velocity, ranging from 5 to 44km/s, is the same as that derived from CO millimeter line emission. This unambiguously proves that these lines are of circumstellar origin and are formed in the AGB ejecta (circumstellar shell expelled during the preceding AGB phase). Furthermore there seems to be a relation between the C2 molecular column density and the expansion velocity, which is attributed to the fact that a higher carbon abundance of the dust leads to a more efficient acceleration of the AGB wind. Using simple assumptions for the location of the molecular lines and molecular abundances, mass-loss rates have been derived from the molecular absorption lines and are comparable to those obtained from CO emission lines and the infrared excess. (6 data files).

  12. Mass Gains of the Antarctic Ice Sheet Exceed Losses

    NASA Technical Reports Server (NTRS)

    Zwally, H. Jay; Li, Jun; Robbins, John; Saba, Jack L.; Yi, Donghui; Brenner, Anita; Bromwich, David

    2012-01-01

    During 2003 to 2008, the mass gain of the Antarctic ice sheet from snow accumulation exceeded the mass loss from ice discharge by 49 Gt/yr (2.5% of input), as derived from ICESat laser measurements of elevation change. The net gain (86 Gt/yr) over the West Antarctic (WA) and East Antarctic ice sheets (WA and EA) is essentially unchanged from revised results for 1992 to 2001 from ERS radar altimetry. Imbalances in individual drainage systems (DS) are large (-68% to +103% of input), as are temporal changes (-39% to +44%). The recent 90 Gt/yr loss from three DS (Pine Island, Thwaites-Smith, and Marie-Bryd Coast) of WA exceeds the earlier 61 Gt/yr loss, consistent with reports of accelerating ice flow and dynamic thinning. Similarly, the recent 24 Gt/yr loss from three DS in the Antarctic Peninsula (AP) is consistent with glacier accelerations following breakup of the Larsen B and other ice shelves. In contrast, net increases in the five other DS of WA and AP and three of the 16 DS in East Antarctica (EA) exceed the increased losses. Alternate interpretations of the mass changes driven by accumulation variations are given using results from atmospheric-model re-analysis and a parameterization based on 5% change in accumulation per degree of observed surface temperature change. A slow increase in snowfall with climate waRMing, consistent with model predictions, may be offsetting increased dynamic losses.

  13. Bipolar nebulae and mass loss from red giant stars

    NASA Technical Reports Server (NTRS)

    Cohen, M.

    1985-01-01

    Observations of several bipolar nebulae are used to learn something of the nature of mass loss from the probable red-giant progenitors of these nebulae. Phenomena discussed are: (1) probable GL 2688's optical molecular emissions; (2) newly discovered very high velocity knots along the axis of OH 0739 - 14, which reveal evidence for mass ejections of + or 300 km/s from the M9 III star embedded in this nebula; (3) the bipolar structure of three extreme carbon stars, and the evidence for periodic mass ejection in IRC + 30219, also at high speed (about 80 km/s); and (4) the curious cool TiO-rich region above Parsamian 13, which may represent the very recent shedding of photospheric material from a cool, oxygen-rich giant. Several general key questions about bipolar nebulae that relate to the process of mass loss from their progenitor stars are raised.

  14. Current hot questions on the s process in AGB stars

    NASA Astrophysics Data System (ADS)

    Lugaro, M.; Campbell, S. W.; D'Orazi, V.; Karakas, A. I.; Garcia-Hernandez, D. A.; Stancliffe, R. J.; Tagliente, G.; Iliadis, C.; Rauscher, T.

    2016-01-01

    Asymptotic giant branch (AGB) stars are a main site of production of nuclei heavier than iron via the s process. In massive (>4 M⊙) AGB stars the operation of the 22Ne neutron source appears to be confirmed by observations of high Rb enhancements, while the lack of Tc in these stars rules out 13C as a main source of neutrons. The problem is that the Rb enhancements are not accompanied by Zr enhancements, as expected by s-process models. This discrepancy may be solved via a better understanding of the complex atmospheres of AGB stars. Second- generation stars in globular clusters (GCs), on the other hand, do not show enhancements in any s-process elements, not even Rb. If massive AGB stars are responsible for the composition of these GC stars, they may have evolved differently in GCs than in the field. In AGB stars of lower masses, 13C is the main source of neutrons and we can potentially constrain the effects of rotation and proton-ingestion episodes using the observed composition of post-AGB stars and of stardust SiC grains. Furthermore, independent asteroseismology observations of the rotational velocities of the cores of red giants and of white dwarves will play a fundamental role in helping us to better constrain the effect of rotation. Observations of carbon-enhanced metal-poor stars enriched in both Ba and Eu may require a neutron flux in-between the s and the r process, while the puzzling increase of Ba as function of the age in open clusters, not accompanied by increase in any other element heavier than iron, require further observational efforts. Finally, stardust SiC provides us high-precision constraints to test nuclear inputs such as neutron-capture cross sections of stable and unstable isotopes and the impact of excited nuclear states in stellar environments.

  15. Presupernova evolution and explosion of massive stars with mass loss

    NASA Astrophysics Data System (ADS)

    Limongi, M.; Chieffi, A.

    2007-08-01

    We review the main properties of solar metallicity massive stars in the range 11-120 Msolar. The influence of the mass loss on the hydrostatic burning stages as well as the final explosion is discussed in some detail. We find that the minimum masses that enter the WNL, WNE and WC stages are 30 Msolar, 35 Msolar and 40 Msolar respectively; the limiting mass between stars exploding as SNII and SNIb/c is between 30 and 35 Msolar the limiting mass between stars forming neutron stars and black holes after the explosion is between 25-30 Msolar. We also discuss the properties of the chemical yields integrated over a Salpeter IMF and we find that stars with M >= 35 Msolar contribute for ~ 60% to the production of C, N and for ~ 40% to the production Sc and s-process elements up to Zr, while they do not produce any intermediate mass element because of the large remnant masses.

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

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  17. High-elevation mass loss of Greenland increasing

    NASA Astrophysics Data System (ADS)

    Andersen, M. L.; Andersen, S. B.; Ahlstrom, A. P.; Stenseng, L.; Skourup, H.; Kristensen, S. S.; Forsberg, R.; Fettweis, X.; Joughin, I. R.

    2013-12-01

    The Greenland Ice Sheet is losing mass at an accelerated pace. Presently, the mass loss is assumed to be distributed approximately equally between loss in the form of surface melt (surface mass balance, SMB) and solid ice discharge (iceberg calving, D) along the margins. As part of the PROMICE project, repeated airborne LIDAR and radar surveys were carried out along the entire margin of the Greenland ice sheet in the years 2007 and 2011, providing bed and surface elevation profiles. Using these profiles, we establish a flux gate along the flight path, passing through 19 drainage basins. To obtain a depth-averaged flow speed, the observed surface flow speeds were adjusted with respect to several different flow regimes defined by the ratio of a SAR-derived surface velocity to ice thickness and driving stress. With the ice thickness and depth-averaged flow speed known we then estimate the solid mass flux passing through the flux gate in 2007 and 2011 in each of the basins. To isolate D (i.e., the contribution to sea level rise from solid ice discharge at the coasts), SMB values for the areas between the gate and the grounding lines in the basins were obtained from a regional climate model. We compare the calculated mass losses between the two years integrated over the entire ice sheet, but also on a basin-by-basin level to investigate internal redistribution of mass between the basins over time. We find a ~3% mean increase in mass loss per year at the ~1600 m elevation of the flux gate.

  18. ADIABATIC MASS LOSS IN BINARY STARS. I. COMPUTATIONAL METHOD

    SciTech Connect

    Ge Hongwei; Chen Xuefei; Han Zhanwen; Webbink, Ronald F. E-mail: mshjell@gmail.co

    2010-07-10

    The asymptotic response of donor stars in interacting binary systems to very rapid mass loss is characterized by adiabatic expansion throughout their interiors. In this limit, energy generation and heat flow through the stellar interior can be neglected. We model this response by constructing model sequences, beginning with a donor star filling its Roche lobe at an arbitrary point in its evolution, holding its specific entropy and composition profiles fixed as mass is removed from the surface. The stellar interior remains in hydrostatic equilibrium. Luminosity profiles in these adiabatic models of mass-losing stars can be reconstructed from the specific entropy profiles and their gradients. These approximations are validated by comparison with time-dependent binary mass transfer calculations. We describe how adiabatic mass-loss sequences can be used to quantify threshold conditions for dynamical timescale mass transfer, and to establish the range of post-common envelope binaries that are allowed energetically. In dynamical timescale mass transfer, the adiabatic response of the donor star drives it to expand beyond its Roche lobe, leading to runaway mass transfer and the formation of a common envelope with its companion star. For donor stars with surface convection zones of any significant depth, this runaway condition is encountered early in mass transfer, if at all; but for main-sequence stars with radiative envelopes, it may be encountered after a prolonged phase of thermal timescale mass transfer, a so-called delayed dynamical instability. We identify the critical binary mass ratio for the onset of dynamical timescale mass transfer as that ratio for which the adiabatic response of the donor star radius to mass loss matches that of its Roche lobe at some point during mass transfer; if the ratio of donor to accretor masses exceeds this critical value, dynamical timescale mass transfer ensues. In common envelope evolution, the dissipation of orbital energy of the

  19. New observations and models of circumstellar CO line emission of AGB stars in the Herschel SUCCESS programme

    NASA Astrophysics Data System (ADS)

    Danilovich, T.; Teyssier, D.; Justtanont, K.; Olofsson, H.; Cerrigone, L.; Bujarrabal, V.; Alcolea, J.; Cernicharo, J.; Castro-Carrizo, A.; García-Lario, P.; Marston, A.

    2015-09-01

    Context. Asymptotic giant branch (AGB) stars are in one of the latest evolutionary stages of low to intermediate-mass stars. Their vigorous mass loss has a significant effect on the stellar evolution, and is a significant source of heavy elements and dust grains for the interstellar medium. The mass-loss rate can be well traced by carbon monoxide (CO) line emission. Aims: We present new Herschel/HIFI and IRAM 30 m telescope CO line data for a sample of 53 galactic AGB stars. The lines cover a fairly large range of excitation energy from the J = 1 → 0 line to the J = 9 → 8 line, and even the J = 14 → 13 line in a few cases. We perform radiative transfer modelling for 38 of these sources to estimate their mass-loss rates. Methods: We used a radiative transfer code based on the Monte Carlo method to model the CO line emission. We assume spherically symmetric circumstellar envelopes that are formed by a constant mass-loss rate through a smoothly accelerating wind. Results: We find models that are consistent across a broad range of CO lines for most of the stars in our sample, i.e., a large number of the circumstellar envelopes can be described with a constant mass-loss rate. We also find that an accelerating wind is required to fit, in particular, the higher-J lines and that a velocity law will have a significant effect on the model line intensities. The results cover a wide range of mass-loss rates (~10-8 to 2 × 10-5 M⊙ yr-1) and gas expansion velocities (2 to 21.5 km s-1) , and include M-, S-, and C-type AGB stars. Our results generally agree with those of earlier studies, although we tend to find slightly lower mass-loss rates by about 40%, on average. We also present "bonus" lines detected during our CO observations. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Based on observations carried out with the IRAM 30 m Telescope. IRAM is

  20. Near-Infrared Mass Loss Diagnostics for Massive Stars

    NASA Technical Reports Server (NTRS)

    Sonneborn, George; Bouret, J. C.

    2010-01-01

    Stellar wind mass loss is a key process which modifies surface abundances, luminosities, and other physical properties of hot, massive stars. Furthermore, mass loss has to be understood quantitatively in order to accurately describe and predict massive star evolution. Two urgent problems have been identified that challenge our understanding of line-driven winds, the so-called weak-wind problem and wind clumping. In both cases, mass-loss rates are drastically lower than theoretically expected (up to a factor 1001). Here we study how the expected spectroscopic capabilities of the James Webb Space Telescope (JWST), especially NIRSpec, could be used to significantly improve constraints on wind density structures (clumps) and deep-seated phenomena in stellar winds of massive stars, including OB, Wolf-Rayet and LBV stars. Since the IR continuum of objects with strong winds is formed in the wind, IR lines may sample different depths inside the wind than UV-optical lines and provide new information about the shape of the velocity field and clumping properties. One of the most important applications of IR line diagnostics will be the measurement of mass-loss rates in massive stars with very weak winds by means of the H I Bracket alpha line, which has been identified as one of the most promising diagnostics for this problem.

  1. The Effects of Stellar Chemistry on the Broad 9-15 Micron Spectral Feature of O-rich AGB Stars

    NASA Astrophysics Data System (ADS)

    Arrant, David J.; Speck, A.

    2013-01-01

    Dust plays an important role in many astrophysical processes. Asymptotic giant branch (AGB) stars expel gas from their surfaces; as it moves away from the star, it cools and condenses to produce dust. Carbon monoxide (CO) is extremely stable and will trap most of the oxygen and carbon. The lesser abundant of carbon and oxygen will be entirely trapped in CO, while the more abundant will have excess atoms available to form dust. AGB stars are divided into carbon-rich (C-rich) stars or oxygen-rich (O-rich) stars. O-rich AGB stars with low mass-loss rates show a 9-15 micron feature, which is attributed to various dust species, such as silicates and oxides. This broad feature is fitted with two overlapping Gaussian functions. The parameters of the Gaussian fits are compared to stellar chemistry properties, such as the elemental abundances (C, N, O, Fe, Ti, Ni, Y, Zr, and Nd) and ratios (C/N, C/O, C/Fe…) in order to assess the effect of chemistry on dust formation.

  2. ALMA observations of the not-so detached shell around the carbon AGB star R Sculptoris

    NASA Astrophysics Data System (ADS)

    Maercker, Matthias

    2016-07-01

    I present our ALMA observations of the CO emission around the carbon AGB star R Sculptoris. The data reveal the known detached shell and a previously unknown, binary induced, spiral shape. The observations confirm a formation of the shell during a thermal pulse about 2300 years ago. The full analysis of the ALMA data shows that the shell around R Scl in fact is entirely filled with molecular gas, and hence not as detached as previously thought. This has implications for the mass-loss rate evolution immediately after the pulse, indicating a much higher mass-loss rate than previously assumed. Comparing the ALMA images to our optical observations of polarised, dust scattered light, we further show that the distributions of the dust and gas coincide almost perfectly, implying a common evolution of the dust and gas, and constraining the wind-driving mechanism. The mass-loss process and amount of mass lost during the thermal pulse cycle affect the chemical evolution of the star, its lifetime on the AGB, and the return of heavy elements to the ISM. New high-resolution ALMA observations constrain the parameters of the binary system and the inner spiral, and will allow for a detailed hydrodynamical modelling of the gas and dust during and after the last thermal pulse. Our results present the only direct measurements of the thermal pulse evolution currently available. They greatly increase our understanding of this fundamental period of stellar evolution, and the implications it has for the chemical evolution of evolved stars, the ISM, and galaxie

  3. Irreversible mass loss of Canadian Arctic Archipelago glaciers

    NASA Astrophysics Data System (ADS)

    Lenaerts, Jan T. M.; Angelen, Jan H.; Broeke, Michiel R.; Gardner, Alex S.; Wouters, Bert; Meijgaard, Erik

    2013-03-01

    The Canadian Arctic Archipelago (CAA) contains the largest volume of glacier ice on Earth outside of Antarctica and Greenland. In the absence of significant calving, CAA glacier mass balance is governed by the difference between surface snow accumulation and meltwater runoff—surface mass balance. Here we use a coupled atmosphere/snow model to simulate present-day and 21st century CAA glacier surface mass balance. Through comparison with Gravity Recovery and Climate Experiment mass anomalies and in situ observations, we show that the model is capable of representing present-day CAA glacier mass loss, as well as the dynamics of the seasonal snow cover on the CAA tundra. Next, we force this model until 2100 with a moderate climate warming scenario (AR5 RCP4.5). We show that enhanced meltwater runoff from CAA glaciers is not sufficiently compensated by increased snowfall. Extrapolation of these results toward an AR5 multimodel ensemble results in sustained 21st century CAA glacier mass loss in the vast majority (>99%) of the ~7000 temperature realizations.

  4. An Analysis and Classification of Dying AGB Stars Transitioning to Pre-Planetary Nebulae

    NASA Technical Reports Server (NTRS)

    Blake, Adam C.

    2011-01-01

    The principal objective of the project is to understand part of the life and death process of a star. During the end of a star's life, it expels its mass at a very rapid rate. We want to understand how these Asymptotic Giant Branch (AGB) stars begin forming asymmetric structures as they start evolving towards the planetary nebula phase and why planetary nebulae show a very large variety of non-round geometrical shapes. To do this, we analyzed images of just-forming pre-planetary nebula from Hubble surveys. These images were run through various image correction processes like saturation correction and cosmic ray removal using in-house software to bring out the circumstellar structure. We classified the visible structure based on qualitative data such as lobe, waist, halo, and other structures. Radial and azimuthal intensity cuts were extracted from the images to quantitatively examine the circumstellar structure and measure departures from the smooth spherical outflow expected during most of the AGB mass-loss phase. By understanding the asymmetrical structure, we hope to understand the mechanisms that drive this stellar evolution.

  5. Pre-Supernova Mass Loss Predictions for Massive Stars

    NASA Astrophysics Data System (ADS)

    Vink, J. S.; de Koter, A.; Kotak, R.

    2008-06-01

    Massive stars and supernovae (SNe) have a huge impact on their environment. Despite their importance, a comprehensive knowledge of which massive stars produce which SNe is hitherto lacking. We use a Monte Carlo method to predict the mass-loss rates of massive stars in the Hertzsprung-Russell Diagram (HRD) covering all phases from the OB main sequence, the unstable Luminous Blue Variable (LBV) stage, to the final Wolf-Rayet (WR) phase. Although WR produce their own metals, a strong dependence of the mass-loss rate on the initial iron abundance is found at sub-solar metallicities (1/10 -- 1/100 solar). This may present a viable mechanism to prevent the loss of angular momentum by stellar winds, which could inhibit GRBs occurring at solar metallicities -- providing a significant boost to the collapsar model. Furthermore, we discuss recently reported quasi-sinusoidal modulations in the radio lightcurves of SN 2001ig and SNe 2003bg. We show that both the sinusoidal behaviour and the recurrence timescale of these modulations are consistent with the predicted mass-loss behaviour of LBVs. We discuss potential ramifications for the ``Conti'' scenario for massive star evolution.

  6. The abundance of HCN in circumstellar envelopes of AGB stars of different chemical type

    NASA Astrophysics Data System (ADS)

    Schöier, F. L.; Ramstedt, S.; Olofsson, H.; Lindqvist, M.; Bieging, J. H.; Marvel, K. B.

    2013-02-01

    Aims: A multi-transition survey of HCN (sub-) millimeter line emission from a large sample of asymptotic giant branch (AGB) stars of different chemical type is presented. The data are analysed and circumstellar HCN abundances are estimated. The sample stars span a large range of properties such as mass-loss rate and photospheric C/O-ratio. The analysis of the new data allows for more accurate estimates of the circumstellar HCN abundances and puts new constraints on chemical models. Methods: In order to constrain the circumstellar HCN abundance distribution a detailed non-local thermodynamic equilibrium (LTE) excitation analysis, based on the Monte Carlo method, is performed. Effects of line overlaps and radiative excitation from dust grains are included. Results: The median values for the derived abundances of HCN (with respect to H2) are 3 × 10-5, 7 × 10-7 and 10-7 for carbon stars (25 stars), S-type AGB stars (19 stars) and M-type AGB stars (25 stars), respectively. The estimated sizes of the HCN envelopes are similar to those obtained in the case of SiO for the same sample of sources and agree well with previous results from interferometric observations, when these are available. Conclusions: We find that there is a clear dependence of the derived circumstellar HCN abundance on the C/O-ratio of the star, in that carbon stars have about two orders of magnitude higher abundances than M-type AGB stars, on average. The derived HCN abundances of the S-type AGB stars have a larger spread and typically fall in between those of the two other types, however, slightly closer to the values for the M-type AGB stars. For the M-type stars, the estimated abundances are much higher than what would be expected if HCN is formed in thermal equilibrium. However, the results are also in contrast to predictions from recent non-LTE chemical models, where very little difference is expected in the HCN abundances between the various types of AGB stars. This publication is based on data

  7. Mass loss on Himalayan glacier endangers water resources

    NASA Astrophysics Data System (ADS)

    Kehrwald, Natalie M.; Thompson, Lonnie G.; Tandong, Yao; Mosley-Thompson, Ellen; Schotterer, Ulrich; Alfimov, Vasily; Beer, Jürg; Eikenberg, Jost; Davis, Mary E.

    2008-11-01

    Ice cores drilled from glaciers around the world generally contain horizons with elevated levels of beta radioactivity including 36Cl and 3H associated with atmospheric thermonuclear bomb testing in the 1950s and 1960s. Ice cores collected in 2006 from Naimona'nyi Glacier in the Himalaya (Tibet) lack these distinctive marker horizons suggesting no net accumulation of mass (ice) since at least 1950. Naimona'nyi is the highest glacier (6050 masl) documented to be losing mass annually suggesting the possibility of similar mass loss on other high-elevation glaciers in low and mid-latitudes under a warmer Earth scenario. If climatic conditions dominating the mass balance of Naimona'nyi extend to other glaciers in the region, the implications for water resources could be serious as these glaciers feed the headwaters of the Indus, Ganges, and Brahmaputra Rivers that sustain one of the world's most populous regions.

  8. Planetological implications of mass loss from the early Sun

    NASA Technical Reports Server (NTRS)

    Whitmire, D. P.; Matese, J. J.; Doyle, L. R.; Reynolds, R. T.

    1991-01-01

    The element lithium is observed to be underabundant in the Sun by a factor of approx. equal to 100. To account for this depletion, Boothroyd et al. (Ap. J., in press 1991) proposed a model in which the Sun's zero-age-main-sequence mass was approx. 1.1 solar magnitude. If this is the explanation for the lithium depletion, then astronomical observations of F/G dwarfs in clusters suggest that the timescale for mass loss is approx. equal to 0.6 Gyr. Assuming this approximate timescale, the authors investigated several planetological implications of the astrophysical model.

  9. Main sequence mass loss and the ages of stars

    NASA Technical Reports Server (NTRS)

    Willson, L. A.

    1989-01-01

    The potentially observable consequences of the pulsation/rotation-induced mass loss from main-sequence A and F stars proposed by Willson et al. (1987) are discussed, reviewing the results of recent investigations. Particular attention is given to (1) evidence for a deficiency in A stars and an excess of F and G stars, as predicted by the theory, (2) cluster HR diagrams and age estimates, and (3) modifications to standard models of solar-system evolution. It is pointed out that the time scales and mass-loss rates required to explain the observed properties of clusters and field stars in this theory are the same as those needed to account for the early development of the solar system.

  10. Loss of atomic oxygen in mass spectrometer ion sources.

    NASA Technical Reports Server (NTRS)

    Lake, L. R.; Nier, A. O.

    1973-01-01

    A gas beam consisting of a mixture of atomic and molecular oxygen has been directed at the ion source of a mass spectrometer like those used in sounding rockets for determining the neutral composition of the lower thermosphere. The loss of atomic oxygen on mass spectrometer surfaces was evaluated by flagging the beam in several ways and comparing the experimental results with predicted values. The results obtained suggest that in rocket flights using similar instruments the atomic oxygen densities computed assuming no-loss conditions may be low by a factor of 2.5. Studies made using a beam containing tracer O-18 indicate that carbon dioxide observed when atomic oxygen enters the source is formed in a reaction involving atomic oxygen from the beam and carbon monoxide from the surfaces bombarded.

  11. Sulphur molecules in the circumstellar envelopes of M-type AGB stars

    NASA Astrophysics Data System (ADS)

    Danilovich, T.; De Beck, E.; Black, J. H.; Olofsson, H.; Justtanont, K.

    2016-04-01

    Aims: The sulphur compounds SO and SO2 have not been widely studied in the circumstellar envelopes of asymptotic giant branch (AGB) stars. By presenting and modelling a large number of SO and SO2 lines in the low mass-loss rate M-type AGB star R Dor, and modelling the available lines of those molecules in a further four M-type AGB stars, we aim to determine their circumstellar abundances and distributions. Methods: We use a detailed radiative transfer analysis based on the accelerated lambda iteration method to model circumstellar SO and SO2 line emission. We use molecular data files for both SO and SO2 that are more extensive than those previously available. Results: Using 17 SO lines and 98 SO2 lines to constrain our models for R Dor, we find an SO abundance of (6.7 ± 0.9) × 10-6 and an SO2 abundance of 5 × 10-6 with both species having high abundances close to the star. We also modelled 34SO and found an abundance of (3.1 ± 0.8) × 10-7, giving an 32SO/34SO ratio of 21.6 ± 8.5. We derive similar results for the circumstellar SO and SO2 abundances and their distributions for the low mass-loss rate object W Hya. For the higher mass-loss rate stars, we find shell-like SO distributions with peak abundances that decrease and peak abundance radii that increase with increasing mass-loss rate. The positions of the peak SO abundance agree very well with the photodissociation radii of H2O. We also modelled SO2 in two higher mass-loss rate stars but our models for these were less conclusive. Conclusions: We conclude that for the low mass-loss rate stars, the circumstellar SO and SO2 abundances are much higher than predicted by chemical models of the extended stellar atmosphere. These two species may also account for all the available sulphur. For the higher mass-loss rate stars we find evidence that SO is most efficiently formed in the circumstellar envelope, most likely through the photodissociation of H2O and the subsequent reaction between S and OH. The S

  12. Chromospheric dust formation, stellar masers and mass loss

    NASA Technical Reports Server (NTRS)

    Stencel, R. E.

    1986-01-01

    A multistep scenario which describes a plausible mass loss mechanism associated with red giant and related stars is outlined. The process involves triggering a condensation instability in an extended chromosphere, leading to the formation of cool, dense clouds which are conducive to the formation of molecules and dust grains. Once formed, the dust can be driven away from the star by radiation pressure. Consistency with various observed phenomena is discussed.

  13. Very Low Energy Supernovae From Neutrino Mass Loss

    NASA Astrophysics Data System (ADS)

    Lovegrove, Elizabeth; Woosley, S. E.

    2013-01-01

    The continuing difficulty of achieving a reliable core-collapse supernova in simulation has led many to speculate about what transients might be visible if a core-collapse supernova fails. If some percentage of such supernovae fail, there may be many more types of transients occurring than are currently being detected and catalogued as supernovae. Even if the original outgoing shock in a collapsing presupernova star fails, one must still consider the hydrodynamic response of the star to the abrupt loss of a small amount of mass via neutrinos as the core forms a protoneutron star. Following a suggestion by Nadezhin (1980), we use the Kepler and CASTRO codes to model the hydrodynamical responses of typical supernova progenitor stars to the loss of approximately 0.2 - 0.5 solar masses of gravitational mass from their centers. In a red supergiant star, a very weak supernova with total kinetic energy ~1047 ergs results. The binding energy of the hydrogen envelope before the explosion is of the same order and, depending upon assumptions regarding the neutrino loss rates, most of it is ejected. Ejection speeds are ~50 km/s and luminosities ~1039 ergs/s are maintained for about a year. A significant part of the energy comes from the recombination of hydrogen. The color of the explosion is extremely red and the events bear some similarity to the detected transients catalogued as "luminous red novae."

  14. Evolution of Mass Loss in Stars of Magellanic Cloud Clusters

    NASA Astrophysics Data System (ADS)

    Hodge, Paul W.

    We propose to continue our study of the brightest main sequence and supergiant stars in two rich clusters, NGC 330 and NGC 2100, in the Magellanic Clouds. These very young globular-like clusters have several supergiants that must have essentially the same age and mass as the brightest main sequence stars. They therefore offer the possibility to follow the evolution of mass loss during supergiant evolution for essentially identical stars, giving information about the final mass of massive stars in the MCs during the later stages of stellar evolution. This, of course, determines the central temperature in their final stages of element synthesis. The MCs, with their somewhat lower metals abundance, can provide us with information about how this process occurs for stars that are chemically quite different from those in the solar neighborhood.

  15. SUPER-AGB-AGB EVOLUTION AND THE CHEMICAL INVENTORY IN NGC 2419

    SciTech Connect

    Ventura, Paolo; D'Antona, Francesca; Carini, Roberta; Di Criscienzo, Marcella; D'Ercole, Annibale; Vesperini, Enrico

    2012-12-20

    We follow the scenario of formation of second-generation stars in globular clusters by matter processed by hot bottom burning (HBB) in massive asymptotic giant branch (AGB) stars and super-AGB stars (SAGB). In the cluster NGC 2419 we assume the presence of an extreme population directly formed from the AGB and SAGB ejecta, so we can directly compare the yields for a metallicity Z = 0.0003 with the chemical inventory of the cluster NGC 2419. At such a low metallicity, the HBB temperatures (well above 10{sup 8} K) allow a very advanced nucleosynthesis. Masses {approx}6 M{sub Sun} deplete Mg and synthesize Si, going beyond Al, so this latter element is only moderately enhanced; sodium cannot be enhanced. The models are consistent with the observations, although the predicted Mg depletion is not as strong as in the observed stars. We predict that the oxygen abundance must be depleted by a huge factor (>50) in the Mg-poor stars. The HBB temperatures are close to the region where other p-capture reactions on heavier nuclei become possible. We show that high potassium abundance found in Mg-poor stars can be achieved during HBB by p-captures on the argon nuclei, if the relevant cross section(s) are larger than listed in the literature or if the HBB temperature is higher. Finally, we speculate that some calcium production is occurring owing to proton capture on potassium. We emphasize the importance of a strong effort to measure a larger sample of abundances in this cluster.

  16. Mass Loss: Its Effect on the Evolution and Fate of High-Mass Stars

    NASA Astrophysics Data System (ADS)

    Smith, Nathan

    2014-08-01

    Our understanding of massive star evolution is in flux due to recent upheavals in our view of mass loss and observations of a high binary fraction among O-type stars. Mass-loss rates for standard metallicity-dependent winds of hot stars are lower by a factor of 2-3 compared with rates adopted in modern stellar evolution codes, due to the influence of clumping on observed diagnostics. Weaker hot star winds shift the burden of H-envelope removal to the winds, pulsations, and eruptions of evolved supergiants, as well as binary mass transfer. Studies of stripped-envelope supernovae, in particular, require binary mass transfer. Dramatic examples of eruptive mass loss are seen in Type IIn supernovae, which have massive shells ejected just a few years earlier. These eruptions are a prelude to core collapse, and may signify severe instabilities in the latest nuclear burning phases. We encounter the predicament that the most important modes of mass loss are also the most uncertain, undermining the predictive power of single-star evolution models. Moreover, the influence of winds and rotation has been evaluated by testing single-star models against observed statistics that, it turns out, are heavily influenced by binary evolution. Altogether, this may alter our view about the most basic outcomes of massive-star mass loss—are Wolf-Rayet stars and Type Ibc supernovae the products of winds, or are they mostly the result of binary evolution and eruptive mass loss? This is not fully settled, but mounting evidence points toward the latter. This paradigm shift impacts other areas of astronomy, because it changes predictions for ionizing radiation and wind feedback from stellar populations, it may alter conclusions about star-formation rates and initial mass functions, it affects the origin of compact stellar remnants, and it influences how we use supernovae as probes of stellar evolution across cosmic time.

  17. Improved GIA correction yields larger Antarctic mass loss.

    NASA Astrophysics Data System (ADS)

    Velicogna, I.; Sutterley, T. C.; Ivins, E. R.; van den Broeke, M. R.

    2014-12-01

    New regional ice deglaciation models have recently been developed to match a variety of geologic, glaciological, and geodetic observations. In Antarctica, these new models exhibit a smaller East Antarctic ice loss since the Last Glacial Maximum, and hence yield a smaller GIA correction to the Antarctic estimates than those predicted by ICE5G. These revised models yield less negative ice mass losses when using GRACE data. Although these new models represent a significant advance in Antarctic GIA modeling, there are still large uncertainties associated with them. One of the large uncertainties is due to the fact that in the East Antarctica interior, the GIA reconstruction is poorly constrained by observations. These new models assume a monotonic decrease in loading in the last 5000 years. We examine the impact of this assumption on the GIA estimates and how a more realistic non-monotonic loading scenario could impact the results and the GRACE ice mass estimates. We use GRACE in combination with output products from the Regional Atmospheric Climate Model (RACMO) and recent studies of deglaciation history to derive an improved GIA correction, which include a non-monotonic loading scenario, is consistent with available geological and geodetic constraints and reconstruction of recent climate history. We find a larger correction, which implies larger losses of the Antarctica ice sheet by about 70 Gt/yr.

  18. Galactic Sodium from AGB Stars

    NASA Astrophysics Data System (ADS)

    Izzard, R. G.; Gibson, B. K.; Stancliffe, R. J.

    2007-11-01

    Galactic chemical evolution (GCE) models which include sodium from type II supernovae (SNe) alone underestimate the abundance of sodium in the interstellar medium by a factor of 2 to 3 over about 3 ridex in metallicity and predict a flat behavior in the evolution of riNafe at super-solar metallicities. Conversely, recent observations of stars with rifeh ˜ +0.4 suggest that riNafe increases at high metallicity. We have combined stellar evolution models of asymptotic giant branch (AGB) and Wolf-Rayet (WR) stars with the latest SN yields in an attempt to resolve these problems dots and have created many more.

  19. Mass loss in main-sequence A-type stars?

    NASA Astrophysics Data System (ADS)

    Lanz, T.; Catala, C.

    1992-04-01

    We present new observations of the H-alpha line profile for five main-sequence A-type stars, where very high SNRs were achieved. A search for weak asymmetries was carried out to detect a stellar wind, but the many telluric absorption lines in this range prevent us from taking the full benefit of the high SNRs. This situation was improved by modeling the telluric absorptions to remove them from the observed spectra, but the H-alpha profiles were nevertheless found to be quite symmetric. We calculated the profile of the H-alpha line for a grid of model atmospheres of an A-type star including a weak wind, in order to assess an upper limit on the mass loss rate. The asymmetry is found to be sensitive to the velocity law and to the turbulent velocity of the wind, but its first moment depends much less on them. The upper limits deduced on the mass loss rate are between 1 and 2 x 10 exp -10 solar mass/yr. An improvement up to a factor 10 could be anticipated if new observations could be secured from a much drier location, achieving similar SNRs.

  20. Very Low Energy Supernovae from Neutrino Mass Loss

    NASA Astrophysics Data System (ADS)

    Lovegrove, Elizabeth; Woosley, S. E.

    2013-06-01

    It now seems likely that some percentage of more massive supernova progenitors do not explode by any of the currently discussed explosion mechanisms. This has led to speculation concerning the observable transients that might be produced if such a supernova fails. Even if a prompt outgoing shock fails to form in a collapsing presupernova star, one must still consider the hydrodynamic response of the star to the abrupt loss of mass via neutrinos as the core forms a protoneutron star. Following a suggestion by Nadezhin, we calculate the hydrodynamical responses of typical supernova progenitor stars to the rapid loss of approximately 0.2-0.5 M ⊙ of gravitational mass from their centers. In a red supergiant star, a very weak supernova with total kinetic energy ~1047 erg results. The binding energy of a large fraction of the hydrogen envelope before the explosion is of the same order and, depending upon assumptions regarding the maximum mass of a neutron star, most of it is ejected. Ejection speeds are ~100 km s-1 and luminosities ~1039 erg s-1 are maintained for about a year. A significant part of the energy comes from the recombination of hydrogen. The color of the explosion is extremely red and the events bear some similarity to "luminous red novae," but have much lower speeds.

  1. Mass Loss from Evolved Stars in Elliptical Galaxies

    NASA Astrophysics Data System (ADS)

    Parriott, Joel R.; Bregman, Joel N.

    2008-07-01

    Most of the X-ray-emitting gas in early-type galaxies probably originates from red giant mass loss, and here we model the interaction between this stellar mass loss and the hot ambient medium. Using two-dimensional hydrodynamic simulations, we adopt a temperature for the ambient medium of 3 × 106 K along with a range of ambient densities and stellar velocities. When the stellar velocity is supersonic relative to the ambient medium, a bow shock occurs, along with a shock driven into the stellar ejecta, which heats only a fraction of the gas. Behind the bow shock, a cool wake develops, but the fast flow of the hot medium causes Kelvin-Helmholtz instabilities to grow and these fingers are shocked and heated (without radiative cooling). Along with the mixing of this wake material with the hot medium, most of the stellar ejecta is heated to approximately the temperature of the hot ambient medium within 2 pc of the star. With the addition of radiative cooling, some wake material remains cool (<105 K), accounting for up to 25% of the stellar mass loss. Less cooled gas survives when the ambient density is lower or when the stellar velocity is higher than in our reference case. These results suggest that some cooled gas should be present in the inner part of early-type galaxies that have a hot ambient medium. These calculations may explain the observed distributed optical emission line gas as well as the presence of dust in early-type galaxies.

  2. Probing Ancient Mass Loss with AKARI's Extended Dust Emission Objects

    NASA Astrophysics Data System (ADS)

    Tomasino, R.; Ueta, T.; Yamamura, I.; Izumiura, H.

    2014-04-01

    We present the results from the calibration and analysis of 166 far-IR extended thermal dust emission objects that were observed with AKARI’s FIS detector. The primary goal is to map the circumstellar shells of evolved stars in detail to excavate the ancient history of dusty mass loss. After establishing an extended aperture photometry method, we characterized the flux dependent slow transient response correction factors for each of the four wavelength bands. Using the new correction factors for extended (far-IR) emission, we present the photometric values that were calculated for the entire data set and also report our work on morphology characterization of the extended dust shells.

  3. Coronal holes - Mass loss driven by magnetic reconnection

    NASA Technical Reports Server (NTRS)

    Mullan, D. J.; Ahmad, I. A.

    1982-01-01

    A nonthermal mechanism for driving coronal hole mass loss is proposed. Three empirical results are noted, namely (1) that polar plumes with short-lived X-ray bright points (XBP) at their base are sites of matter flow sufficient to account for the total solar mass flux, (2) that solar wind densities are positively correlated with the number of XBP in coronal holes, and (3) that XBP are associated with newly emerged magnetic flux. It is noted that since the dynamical development following the onset of nonequilibrium is a hitherto unsolved problem, subsequent features in the scenario described here are relatively speculative. It is proposed that bubbles of matter ejected from magnetic reconnection sites in polar plumes drive the solar wind in coronal holes.

  4. Corotation lag limit on mass-loss rate from Io

    NASA Technical Reports Server (NTRS)

    Huang, T. S.; Siscoe, G. L.

    1987-01-01

    Considering rapid escape of H2O from Io during an early hot evolutionary epoch, an H2O plasma torus is constructed by balancing dissociation and ionization products against centrifugally driven diffusion, including for the first time the effects of corotation lag resulting from mass loading. Two fundamental limits are found as the mass injection rate increases: (1) an 'ignition' limit of 1.1 x 10 to the 6th kg/s, beyond which the torus cannot ionize itself and photoionization dominates; and (2) the ultimate mass loading limit of 1.3 x 10 to the 7th kg/s, which occurs when neutrals newly created by charge exchange and recombination cannot leave the torus, thereby bringing magnetospherically driven transport to a halt. Connecting this limit with the variations of Io's temperature in its early evolution epoch gives an estimate of the upper limit on the total mass loss from Io, about 3.0 x 10 to the 20th kg (for high-opacity nebula) and about 8.9 x 10 to the 20th kg (for low-opacity nebula). These limits correspond to eroding 8 km and 22 km of H2O from the surface. It is concluded that compared to the other Galilean satellites, Io was created basically dry.

  5. Mass-loss Rates for Very Massive Stars Up to 300 Solar Masses

    NASA Astrophysics Data System (ADS)

    Vink, J. S.

    2011-06-01

    One of the key questions in Astrophysics concerns the issue of whether there exists an upper mass limit to stars and if so, what physical mechanism determines this upper limit. Here we present the latest mass-loss predictions for the most massive stars in our Universe - in the mass range up to 300 solar masses - using a novel hydrodynamic method that includes the important effects of multiple photons interactions, allowing us to predict the rate of mass loss and the wind terminal velocity simultaneously. Our model stars have a high Eddington factor (Γ) and we find an upturn in the mass-loss versus Γ dependence, where the model winds become optically thick. This is also the point where our wind efficiency numbers - defined as the wind momentum over the photon momentum - surpass the single-scattering limit (of η = 1), reaching wind efficiency numbers up to η ≃ 2.5. Our modelling indicates a natural transition from common O-type stars to Wolf-Rayet characteristics when the wind becomes optically thick. This "transitional" behaviour is also reflected in the wind acceleration parameter β, which naturally reaches values as high as 1.5-2, as well as in the spectral morphology of the He II line at 4686Å - characteristic for Of and late WN stars. In Wolf-Rayet galaxy research, the feature is sometimes referred to as "the blue bump".

  6. Mass Loss and Surface Displacement Estimates in Greenland from GRACE

    NASA Astrophysics Data System (ADS)

    Jensen, Tim; Forsberg, Rene

    2015-04-01

    The estimation of ice sheet mass changes from GRACE is basically an inverse problem, the solution is non-unique and several procedures for determining the mass distribution exists. We present Greenland mass loss results from two such procedures, namely a direct spherical harmonic inversion procedure possible through a thin layer assumption, and a generalized inverse masscon procedure. These results are updated to the end of 2014, including the unusual 2013 mass gain anomaly, and show a good agreement when taking into account leakage from the Canadian Icecaps. The GRACE mass changes are further compared to GPS uplift data on the bedrock along the edge of the ice sheet. The solid Earth deformation is assumed to consist of an elastic deformation of the crust and an anelastic deformation of the underlying mantle (GIA). The crustal deformation is due to current surface loading effects and therefore contains a strong seasonal component of variation, superimposed on a secular trend. The majority of the anelastic GIA deformation of the mantle is believed to be approximately constant. An accelerating secular trend and seasonal changes, as seen in Greenland, is therefore assumed to be due to elastic deformation from changes in surface mass loading from the ice sheet. The GRACE and GPS comparison is only valid by assuring that the signal content of the two observables are consistent. The GPS receivers are measuring movement at a single point on the bedrock surface, and therefore sensitive to a limited loading footprint, while the GRACE satellites on the other hand measures a filtered, attenuated gravitational field, at an altitude of approximately 500 km, making it sensitive to a much larger area. Despite this, the seasonal loading signal in the two observables show a reasonably good agreement.

  7. The {sup 13}C(α,n){sup 16}O reaction as a neutron source for the s-process in AGB low-mass stars

    SciTech Connect

    Trippella, O.; Busso, M.; La Cognata, M.; Spitaleri, C.; Guardo, G. L.; Lamia, L.; Puglia, S. M.R.; Romano, S.; Spartà, R.; Kiss, G. G.; Rogachev, G. V.; Avila, M.; Koshchiy, E.; Kuchera, A.; Santiago, D.; Mukhamedzhanov, A. M.; Maiorca, E.; Palmerini, S.

    2014-05-09

    The {sup 13}C(α,n){sup 16}O reaction is considered to be the most important neutron source for producing the main component of the s-process in low mass stars. In this paper we focus our attention on two of the main open problems concerning its operation as a driver for the slow neutron captures. Recently, a new measurement of the {sup 13}C(α,n){sup 16}O reaction rate was performed via the Trojan Horse Method greatly increasing the accuracy. Contemporarily, on the modelling side, magnetic mechanisms were suggested to justify the production of the {sup 13}C pocket, thus putting the s-process in stars on safe physical ground. These inputs allow us to reproduce satisfactorily the solar distribution of elements.

  8. The 13C(α,n)16O reaction as a neutron source for the s-process in AGB low-mass stars

    NASA Astrophysics Data System (ADS)

    Trippella, O.; Busso, M.; La Cognata, M.; Spitaleri, C.; Kiss, G. G.; Rogachev, G. V.; Mukhamedzhanov, A. M.; Avila, M.; Guardo, G. L.; Koshchiy, E.; Kuchera, A.; Lamia, L.; Maiorca, E.; Palmerini, S.; Puglia, S. M. R.; Romano, S.; Santiago, D.; Spartà, R.

    2014-05-01

    The 13C(α,n)16O reaction is considered to be the most important neutron source for producing the main component of the s-process in low mass stars. In this paper we focus our attention on two of the main open problems concerning its operation as a driver for the slow neutron captures. Recently, a new measurement of the 13C(α,n)16O reaction rate was performed via the Trojan Horse Method greatly increasing the accuracy. Contemporarily, on the modelling side, magnetic mechanisms were suggested to justify the production of the 13C pocket, thus putting the s-process in stars on safe physical ground. These inputs allow us to reproduce satisfactorily the solar distribution of elements.

  9. A search for water maser emission toward obscured post-AGB star and planetary nebula candidates

    NASA Astrophysics Data System (ADS)

    Gómez, J. F.; Rizzo, J. R.; Suárez, O.; Palau, A.; Miranda, L. F.; Guerrero, M. A.; Ramos-Larios, G.; Torrelles, J. M.

    2015-06-01

    Context. Water maser emission at 22 GHz is a useful probe for studying the transition between the nearly spherical mass loss in the asymptotic giant branch (AGB) to a collimated one in the post-AGB phase. In their turn, collimated jets in the post-AGB phase could determine the shape of planetary nebulae once photoionization starts. Aims: We intend to find new cases of post-AGB stars and planetary nebulae (PNe) with water maser emission, including some especially interesting and rare types: water fountains (evolved objects with high velocity collimated jets traced by water masers) or water-maser-emitting PNe. Since previous studies have shown a higher detection rate of water maser emission in evolved objects that are optically obscured, we selected a sample that contains a significant fraction of post-AGB and young PN candidate sources showing signs of strong obscuration. Methods: We searched for water maser emission in 133 evolved objects using the radio telescopes in Robledo de Chavela, Parkes, and Green Bank. Results: We detected water maser emission in 15 sources of our sample, of which seven are reported here for the first time (IRAS 13483-5905, IRAS 14249-5310, IRAS 15408-5413, IRAS 17021-3109, IRAS 17348-2906, IRAS 17393-2727, and IRAS 18361-1203). We identified three water fountain candidates: IRAS 17291-2147, with a total velocity spread of ≃96 km s-1 in its water maser components and two sources (IRAS 17021-3109 and IRAS 17348-2906) that show water maser emission whose velocity lies outside the velocity range covered by OH masers. We have also identified IRAS 17393-2727 as a possible new water-maser-emitting PN. Conclusions: The detection rate is higher in obscured objects (14%) than in those with optical counterparts (7%), which is consistent with previous results. Water maser emission seems to be common in objects that are bipolar in the near-IR (43% detection rate in such sources). The water maser spectra of water fountain candidates like IRAS 17291

  10. Mass loss from cool stars, facts, fads, and fallacies

    NASA Technical Reports Server (NTRS)

    Dupree, A. K.

    1982-01-01

    The accumulation of observational material (ultraviolet spectroscopic measures, quantitative optical spectroscopy, and X-ray photometry) and its use in discerning the presence and character of mass loss across the cool half of the H-R diagram and establishing constraints on theoretical models are discussed. Analogies with closed and open solar magnetic structures are found. Two determinants of atmospheric wind structure, temperature and gravity, may suffice in a most superficial way to define the wind and atmospheric structure in a star, however it is apparent that there is still a missing parameter which may stem from magnetic activity and its particular configuration. Theories that appear successful in reproducing observed line profiles, wind temperatures, and terminal velocities incorporate Alfven wave heating and momentum deposition. Successive observations of an active binary (lambda and G8III-IV) and a supergiant star, alpha Aqr (G2 Ib) revealed that magnetic activity and perhaps mass loss occur on restricted regions of a stellar surface and that long-term structures are present in the wind. These phenomena are present in the solar atmosphere and wind and may be considered a general characteristic of stellar winds.

  11. Nucleosynthesis in AGB Stars Traced by Oxygen Isotopic Ratios

    NASA Astrophysics Data System (ADS)

    De Nutte, R.; Decin, L.; Olofsson, H.; de Koter, A.; Lombaert, R.; Milam, S.; Ramstedt, S.

    2015-08-01

    Isotopic ratios are by far the best diagnostic tracers of the stellar origin of elements, as they are very sensitive to the precise conditions in the nuclear burning regions. They allow us to give direct constraints on stellar evolution models and on the progenitor mass. However, up to now different isotopic ratios have been well constrained for only a handful of Asymptotic Giant Branch (AGB) stars. We present new data on isotopologue lines of a well-selected sample of AGB stars, covering the three spectral classes of C-, S- and M-type stars. We report on the first efforts made in determining accurate isotopologue fractions, focusing on oxygen isotopes which are a crucial tracer of the poorly constrained extra mixing processes in stellar atmospheres.

  12. A Complete Sample of Hot Post-AGB Stars in Globular Clusters

    NASA Technical Reports Server (NTRS)

    Landsman, W.; Moehler, S.; Napiwotzki, R.; Heber, U.; Sweigart, A.; Catelan, M.; Stecher, T.

    1999-01-01

    Ultraviolet images of globular clusters are often dominated by one or two "UV-bright" stars. The most luminous of these are believed to be post-AGB stars, which go through a luminous UV-bright phase as they leave the AGB and move rapidly across the HR diagram toward their final white dwarf state. During the two flights of the ASTRO observatory in 1990 and 1995, the Ultraviolet Imaging Telescope (UIT, Stecher 1997, PASP, 109, 584) was used to obtained ultraviolet (1600 A) images of 14 globular clusters. These images provide a complete census of hot (> 8000 K) post-AGB stars in the observed globular clusters, because the 40' field of view of UIT is large enough to image the entire population of most Galactic globulars, and because the dominant cool star population is suppressed in ultraviolet images, allowing UV-bright stars to be detected into the cluster core. We have begun a program of optical and STIS ultraviolet spectroscopy to determine the fundamental stellar parameters (\\log L, T_eff, \\log g) of all the hot post-AGB candidates discovered on the UIT images. Among the goals of our program are to test theoretical post-AGB lifetimes across the HR diagram, and to estimate the mass of the currently forming white dwarfs in globular clusters. Two trends are already apparent in our survey. First, the UV-selected sample has removed a bias against the detection of the hottest post-AGB stars, and resulted in the discovery of five cluster post-AGB stars with Teff > 50,000 K. Second, most of the new discoveries have been lower luminosity (2.5 $<$\\log L $<$ 3.0) than expected for stars which leave the AGB during the thermally pulsating phase.

  13. SPUF - a simple polyurethane foam mass loss and response model.

    SciTech Connect

    Hobbs, Michael L.; Lemmon, Gordon H.

    2003-07-01

    A Simple PolyUrethane Foam (SPUF) mass loss and response model has been developed to predict the behavior of unconfined, rigid, closed-cell, polyurethane foam-filled systems exposed to fire-like heat fluxes. The model, developed for the B61 and W80-0/1 fireset foam, is based on a simple two-step mass loss mechanism using distributed reaction rates. The initial reaction step assumes that the foam degrades into a primary gas and a reactive solid. The reactive solid subsequently degrades into a secondary gas. The SPUF decomposition model was implemented into the finite element (FE) heat conduction codes COYOTE [1] and CALORE [2], which support chemical kinetics and dynamic enclosure radiation using 'element death.' A discretization bias correction model was parameterized using elements with characteristic lengths ranging from 1-mm to 1-cm. Bias corrected solutions using the SPUF response model with large elements gave essentially the same results as grid independent solutions using 100-{micro}m elements. The SPUF discretization bias correction model can be used with 2D regular quadrilateral elements, 2D paved quadrilateral elements, 2D triangular elements, 3D regular hexahedral elements, 3D paved hexahedral elements, and 3D tetrahedron elements. Various effects to efficiently recalculate view factors were studied -- the element aspect ratio, the element death criterion, and a 'zombie' criterion. Most of the solutions using irregular, large elements were in agreement with the 100-{micro}m grid-independent solutions. The discretization bias correction model did not perform as well when the element aspect ratio exceeded 5:1 and the heated surface was on the shorter side of the element. For validation, SPUF predictions using various sizes and types of elements were compared to component-scale experiments of foam cylinders that were heated with lamps. The SPUF predictions of the decomposition front locations were compared to the front locations determined from real-time X

  14. Decomposition Kinetics for Mass Loss and Heat Released for HMX

    SciTech Connect

    Weese, R K; Burnham, A K

    2004-07-27

    Nucleation-growth kinetic expressions are derived for thermal decomposition of HMX from a variety of types of data, including mass loss for isothermal and constant rate heating in an open pan, and heat flow for isothermal and constant rate heating in open and closed pans. Conditions are identified in which thermal runaway is small to nonexistent, which typically means temperatures less than 255 C and heating rates less than 1 C/min. Activation energies are typically in the 140 to 150 kJ/mol regime for open pan experiments and about 160 kJ/mol for sealed pan experiments. The reaction clearly displays more than one process, and most likely three processes, which are most clearly evident in open pan experiments. The reaction is accelerated for closed pan experiments, and one global reaction appears to fit the data well.

  15. Mass Loss from the Central Star of NGC 7009

    NASA Technical Reports Server (NTRS)

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

    2006-01-01

    Observations of NGC 7009, including its central star HD 200516, have been obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite, providing spectra covering 905-1187 A with spectral resolution of 15 kilometers per second. One observation was made with the 30x30 arcsec aperture and includes the star plus the entire nebula. A second series of observations used the 1.25x20 arcsec slit, significantly reducing the nebular 'contamination' of the stellar spectrum. This paper discusses the spectrum of the central star. A strong FUV continuum, as expected for Teff=82,000K, dominates the spectrum. The most prominent spectral feature is a very strong P-Cygni profile of O VI 1032-1038. This paper presents models of the stellar spectrum and the wind features to further refine the stellar parameters and mass loss rate.

  16. Highly fractionated mass loss from the atmosphere of Pluto

    NASA Astrophysics Data System (ADS)

    Yen, Chien-Chang; Taam, Ronald E.; Liang, Mao-Chang

    2014-11-01

    Molecules can escape readily from the atmosphere of Pluto. Under the framework of hydrodynamic approximation, it was generally accepted that the process produced rather small isotopic fractionation. Here, we show that the escape highly fractionates the isotopic composition of nitrogen. The process preferentially selects lighter species, with an escape probability a factor of ~3 higher for the lighter isotopologue. The validity of the approach may be testable if the isotopic composition of the outer most regions can be measured. The property of the selection can significantly modify the isotopic composition of the atmosphere, leaving the present-day atmosphere isotopically heavier than the ancient one. This also impacts the current view of the evolution of planetary atmospheres. Venus, for example, may not need that much mass loss, in order to explain the current D/H ratio.

  17. Detection of CI line emission from the detached CO shell of the AGB star R Sculptoris

    NASA Astrophysics Data System (ADS)

    Olofsson, H.; Bergman, P.; Lindqvist, M.

    2015-10-01

    Context. Stars on the asymptotic giant branch (AGB) lose substantial amounts of matter, to the extent that they are important for the chemical evolution of, and dust production in, the Universe. The mass loss is believed to increase gradually with age on the AGB, but it may also occur in the form of bursts, possibly related to the thermal pulsing phenomenon. Detached, geometrically thin, CO shells around carbon stars are good signposts of brief and intense mass ejection. Aims: We aim to put further constraints on the physical properties of detached CO shells around AGB stars. Methods: The photodissociation of CO and other carbon-bearing species in the shells leads to the possibility of detecting lines from neutral carbon. We have therefore searched for the CI(3P1-3P0) line at 492 GHz towards two carbon stars, S Sct and R Scl, with detached CO shells of different ages, ≈8000 and 2300 years, respectively. Results: The CI(3P1-3P0) line was detected towards R Scl. The line intensity is dominated by emission from the detached shell. The detection is at a level consistent with the neutral carbon coming from the full photodissociation of all species except CO, and with only limited photoionisation of carbon. The best fit to the observed 12CO and 13CO line intensities, assuming a homogeneous shell, is obtained for a shell mass of ≈0.002 M⊙, a temperature of ≈100 K, and a CO abundance with respect to H2 of 10-3. The estimated CI/CO abundance ratio is ≈0.3 for the best-fit model. However, a number of arguments point in the direction of a clumpy medium, and a viable interpretation of the data within such a context is provided. Based on observations with the Atacama Pathfinder EXperiment (APEX) telescope. APEX is a collaboration between the Max-Planck-Institut für Radioastronomie, the European Southern Observatory, and the Onsala Space Observatory.

  18. Telomerized presenescent osteoblasts prevent bone mass loss in vivo.

    PubMed

    Yudoh, K; Nishioka, K

    2004-06-01

    Previously, we showed that human osteoblasts expressing the human telomerase reverse transcriptase (hTERT) gene exhibited specific survival advantages--the result of breaching the replicative senescence barrier and maintaining the phenotypic and functional properties of primary osteoblasts in vitro over the total replicative capacity of primary osteoblasts. We postulated that rejuvenated osteoblasts may have a potential to correct bone loss or osteopenia in age-related osteoporotic diseases. In the present study, we studied whether telomerized presenescent osteoblasts prevent bone mass loss in vivo. After obtaining the informed consent from a patient with osteoarthritis who underwent the arthroplastic knee surgery, osteoblastic cells were isolated from donor bone sample. We transfected the gene encoding hTERT into human osteoblastic cells. Human bone fragments from a donor were incubated with human hTERT-transfected presenescent (in vitro aged) osteoblasts or mock-transfected presenescent osteoblasts in culture medium containing Matrigel. We subcutaneously implanted human bone fragments with telomerized presenescent osteoblasts or primary presenescent osteoblasts as three-dimensional Matrigel xenografts in severe combined immunodeficiency (SCID) mice (each group: six mice) and analyzed the grafts at 6 weeks after implantation. We also determined whether telomerized osteoblasts affect the bone-forming capacity in vivo, using a well-established mouse transplantation model in which ceramic hydroxyapatite/tricalcium phosphate particles are used as carrier vehicle. Telomerized presenescent osteoblasts were rejuvenated, and maintained the functional properties of young osteoblasts in vitro. Bone mineral content (BMC) and bone mineral density (BMD) were measured by ash weight and dual-energy X-ray absorptiometry, respectively. Whereas BMC and BMD of human bone fragments, which were inoculated with aged osteoblasts in SCID mice, decreased with time, telomerized

  19. Mass Loss from the Nuclei of Active Galaxies

    NASA Technical Reports Server (NTRS)

    Crenshaw, Michael; Kraemer, Steven B.; George, Ian M.

    2003-01-01

    Blueshifted absorption lines in the UV and X-ray spectra of active galaxies reveal the presence of massive outflows of ionized gas from their nuclei. The intrinsic UV and X-ray absorbers show large global covering factors of the central continuum source, and the inferred mass loss rates are comparable to the mass accretion rates. Many absorbers show variable ionic column densities which are attributed to a combination of variable ionizing flux and motion of gas into and out of the line of sight . Detailed studies of the intrinsic absorbers. with the assistance of monitoring observations and photoionization models. provide constraints on their kinematics] physical conditions. and locations relative to the central continuum source. which range from the inner nucleus (approx.0.01 pc) to the galactic disk or halo (approx.10 kpc) . Dynamical models that make use of thermal winds. radiation pressure. and/or hydromagnetic flows have reached a level of sophistication that permits comparisons with the observational constraints .

  20. Gravitational mass of positron from LEP synchrotron losses

    PubMed Central

    Kalaydzhyan, Tigran

    2016-01-01

    General relativity(GR) is the current description of gravity in modern physics. One of the cornerstones of GR, as well as Newton’s theory of gravity, is the weak equivalence principle (WEP), stating that the trajectory of a freely falling test body is independent of its internal structure and composition. WEP is known to be valid for the normal matter with a high precision. However, due to the rarity of antimatter and weakness of the gravitational forces, the WEP has never been confirmed for antimatter. The current direct bounds on the ratio between the gravitational and inertial masses of the antihydrogen do not rule out a repulsive nature for the antimatter gravity. Here we establish an indirect bound of 0.13% on the difference between the gravitational and inertial masses of the positron (antielectron) from the analysis of synchrotron losses at the Large Electron-Positron collider (LEP). This serves as a confirmation of the conventional gravitational properties of antimatter without common assumptions such as, e.g., coupling of gravity to virtual particles, dynamics of distant astrophysical sources and the nature of absolute gravitational potentials. PMID:27461548

  1. Gravitational mass of positron from LEP synchrotron losses

    NASA Astrophysics Data System (ADS)

    Kalaydzhyan, Tigran

    2016-07-01

    General relativity(GR) is the current description of gravity in modern physics. One of the cornerstones of GR, as well as Newton’s theory of gravity, is the weak equivalence principle (WEP), stating that the trajectory of a freely falling test body is independent of its internal structure and composition. WEP is known to be valid for the normal matter with a high precision. However, due to the rarity of antimatter and weakness of the gravitational forces, the WEP has never been confirmed for antimatter. The current direct bounds on the ratio between the gravitational and inertial masses of the antihydrogen do not rule out a repulsive nature for the antimatter gravity. Here we establish an indirect bound of 0.13% on the difference between the gravitational and inertial masses of the positron (antielectron) from the analysis of synchrotron losses at the Large Electron-Positron collider (LEP). This serves as a confirmation of the conventional gravitational properties of antimatter without common assumptions such as, e.g., coupling of gravity to virtual particles, dynamics of distant astrophysical sources and the nature of absolute gravitational potentials.

  2. Gravitational mass of positron from LEP synchrotron losses.

    PubMed

    Kalaydzhyan, Tigran

    2016-01-01

    General relativity(GR) is the current description of gravity in modern physics. One of the cornerstones of GR, as well as Newton's theory of gravity, is the weak equivalence principle (WEP), stating that the trajectory of a freely falling test body is independent of its internal structure and composition. WEP is known to be valid for the normal matter with a high precision. However, due to the rarity of antimatter and weakness of the gravitational forces, the WEP has never been confirmed for antimatter. The current direct bounds on the ratio between the gravitational and inertial masses of the antihydrogen do not rule out a repulsive nature for the antimatter gravity. Here we establish an indirect bound of 0.13% on the difference between the gravitational and inertial masses of the positron (antielectron) from the analysis of synchrotron losses at the Large Electron-Positron collider (LEP). This serves as a confirmation of the conventional gravitational properties of antimatter without common assumptions such as, e.g., coupling of gravity to virtual particles, dynamics of distant astrophysical sources and the nature of absolute gravitational potentials. PMID:27461548

  3. Luminous Blue Variables, Cool Hypergiants, and Supernova Impostors: The Role of Episodic Mass Loss

    NASA Astrophysics Data System (ADS)

    Mehner, A.; de Wit, W. J.; Baade, D.; Boffin, H. M. J.; Davidson, K.; Groh, J.; Humphreys, R. M.; Martayan, C.; Oudmaijer, R. D.; Rivinius, T.; Selman, F.; Steffen, W.

    2015-12-01

    The role of mass loss, especially episodic mass loss, in evolved massive stars is one of the outstanding questions in stellar evolution theory. IFU observations can provide superb information on the recent mass-loss history and the evolutionary stages. With VLT MUSE we have observed a representative sample of massive stars from different evolved stellar classes that underwent episodic mass loss, which gave rise to extended nebulae. The structural inhomogeneities and associated velocity differences in the nebulae are tracers of the mass-loss history. The simultaneous observation of all lines at each position in the nebulae provides very accurate line ratios for physical diagnostics.

  4. IMPLICATIONS OF MASS AND ENERGY LOSS DUE TO CORONAL MASS EJECTIONS ON MAGNETICALLY ACTIVE STARS

    SciTech Connect

    Drake, Jeremy J.; Cohen, Ofer; Yashiro, Seiji; Gopalswamy, Nat

    2013-02-20

    Analysis of a database of solar coronal mass ejections (CMEs) and associated flares over the period 1996-2007 finds well-behaved power-law relationships between the 1-8 A flare X-ray fluence and CME mass and kinetic energy. We extrapolate these relationships to lower and higher flare energies to estimate the mass and energy loss due to CMEs from stellar coronae, assuming that the observed X-ray emission of the latter is dominated by flares with a frequency as a function of energy dn/dE = kE {sup -{alpha}}. For solar-like stars at saturated levels of X-ray activity, the implied losses depend fairly weakly on the assumed value of {alpha} and are very large: M-dot {approx}5 Multiplication-Sign 10{sup -10} M{sub sun} yr{sup -1} and E-dot {approx}0.1 L{sub sun}. In order to avoid such large energy requirements, either the relationships between CME mass and speed and flare energy must flatten for X-ray fluence {approx}> 10{sup 31} erg, or the flare-CME association must drop significantly below 1 for more energetic events. If active coronae are dominated by flares, then the total coronal energy budget is likely to be up to an order of magnitude larger than the canonical 10{sup -3} L {sub bol} X-ray saturation threshold. This raises the question of what is the maximum energy a magnetic dynamo can extract from a star? For an energy budget of 1% of L {sub bol}, the CME mass loss rate is about 5 Multiplication-Sign 10{sup -11} M {sub Sun} yr{sup -1}.

  5. Mass loss as a driving mechanism of tectonics of Enceladus

    NASA Astrophysics Data System (ADS)

    Czechowski, Leszek

    2015-04-01

    Summary We suggest that the mass loss from South Polar Terrain (SPT) is the main driving force of the following tectonic processes on Enceladus: subsidence of SPT, flow in the mantle and motion of plates. 1. Introduction Enceladus, a satellite of Saturn, is the smallest celestial body in the Solar System where volcanic activity is observed. Every second, the mass of ~200 kg is ejected into space from the South Polar Terrain (SPT) - [1, 2, 3]. The loss of matter from the body's interior should lead to global compression of the crust. Typical effects of compression are: thrust faults, folding and subduction. However, such forms are not dominant on Enceladus. We propose here special tectonic model that could explain this paradox. 2. Subsidence of SPT and tectonics The volatiles escape from the hot region through the fractures forming plumes in the space. The loss of the volatiles results in a void, an instability, and motion of solid matter into the hot region to fill the void. The motion includes : Subsidence of the 'lithosphere' of SPT. Flow of the matter in the mantle. Motion of plates adjacent to SPT towards the active region. If emerging void is being filled by the subsidence of SPT only, then the velocity of subsidence is ~0.05 mm-yr-1. However, all three types of motion are probably important, so the subsidence is slower but mantle flow and plates' motion also play a role in filling the void. Note that in our model the reduction of the crust area is not a result of compression but it is a result of the plate sinking. Therefore the compressional surface features do not have to be dominant. 3. Models of subsidence The numerical model of suggested process of subsidence is developed. It is based on the typical set of equation: Navier-Stokes equation for incompressible viscous liquid, equation of continuity and equation of heat conduction. The Newtonian and non-Newtonian rheologies are used. The preliminary results of the model indicate that the subsidence rate of

  6. Reducing uncertainties in projections of Antarctic ice mass loss

    NASA Astrophysics Data System (ADS)

    Durand, G.; Pattyn, F.

    2015-11-01

    Climate model projections are often aggregated into multi-model averages of all models participating in an intercomparison project, such as the Coupled Model Intercomparison Project (CMIP). The "multi-model" approach provides a sensitivity test to the models' structural choices and implicitly assumes that multiple models provide additional and more reliable information than a single model, with higher confidence being placed on results that are common to an ensemble. A first initiative of the ice sheet modeling community, SeaRISE, provided such multi-model average projections of polar ice sheets' contribution to sea-level rise. The SeaRISE Antarctic numerical experiments aggregated results from all models devoid of a priori selection, based on the capacity of such models to represent key ice-dynamical processes. Here, using the experimental setup proposed in SeaRISE, we demonstrate that correctly representing grounding line dynamics is essential to infer future Antarctic mass change. We further illustrate the significant impact on the ensemble mean and deviation of adding one model with a known bias in its ability of modeling grounding line dynamics. We show that this biased model can hardly be identified from the ensemble only based on its estimation of volume change, as ad hoc and untrustworthy parametrizations can force any modeled grounding line to retreat. However, tools are available to test parts of the response of marine ice sheet models to perturbations of climatic and/or oceanic origin (MISMIP, MISMIP3d). Based on recent projections of Pine Island Glacier mass loss, we further show that excluding ice sheet models that do not pass the MISMIP benchmarks decreases the mean contribution and standard deviation of the multi-model ensemble projection by an order of magnitude for that particular drainage basin.

  7. The loss of muscle mass and sarcopenia: non hormonal intervention.

    PubMed

    Sanchis-Gomar, Fabian; Gómez-Cabrera, Mari Carmen; Viña, Jose

    2011-12-01

    Muscle aging is a key component of the increase in frailty in human populations. The generation of critical levels of power is a prerequisite to perform simple tasks of daily living, such as rising from a chair or climbing stairs. There is great scientific and social interest to determine which behaviors can lead to the maintenance of the muscle mass in young immobilized subjects and in the elderly. Several hormonal treatments have been proposed for the treatment of sarcopenia. However, the side effects associated to these treatments emphasize the need of finding non-toxic and non-hormonal treatments that help increase muscle strength, improve muscle function, and decrease the degree of dependency in the old population. Recently, several studies have shed new light on this topic. Any medical efforts to develop treatments to prevent muscle dysfunction leading to sarcopenia, and eventually frailty, will be a major breakthrough in the public health in advances countries. Moreover, any significant improvement in the loss of muscle function will be a major breakthrough in the health and welfare of the population. PMID:21920428

  8. A model on CME/Flare initiation: Loss of Equilibrium caused by mass loss of quiescent prominences

    NASA Astrophysics Data System (ADS)

    Miley, George; Chon Nam, Sok; Kim, Mun Song; Kim, Jik Su

    2015-08-01

    Coronal Mass Ejections (CMEs) model should give an answer to enough energy storage for giant bulk plasma into interplanetary space to escape against the sun’s gravitation and its explosive eruption. Advocates of ‘Mass Loading’ model (e.g. Low, B. 1996, SP, 167, 217) suggested a simple mechanism of CME initiation, the loss of mass from a prominence anchoring magnetic flux rope, but they did not associate the mass loss with the loss of equilibrium. The catastrophic loss of equilibrium model is considered as to be a prospective CME/Flare model to explain sudden eruption of magnetic flux systems. Isenberg, P. A., et al (1993, ApJ, 417, 368)developed ideal magnetohydrodynamic theory of the magnetic flux rope to show occurrence of catastrophic loss of equilibrium according to increasing magnetic flux transported into corona.We begin with extending their study including gravity on prominence’s material to obtain equilibrium curves in case of given mass parameters, which are the strengths of the gravitational force compared with the characteristic magnetic force. Furthermore, we study quasi-static evolution of the system including massive prominence flux rope and current sheet below it to obtain equilibrium curves of prominence’s height according to decreasing mass parameter in a properly fixed magnetic environment. The curves show equilibrium loss behaviors to imply that mass loss result in equilibrium loss. Released fractions of magnetic energy are greater than corresponding zero-mass case. This eruption mechanism is expected to be able to apply to the eruptions of quiescent prominences, which is located in relatively weak magnetic environment with 105 km of scale length and 10G of photospheric magnetic field.

  9. The superwind mass-loss rate of the metal-poor carbon star LI-LMC 1813 in the LMC cluster KMHK 1603

    NASA Astrophysics Data System (ADS)

    van Loon, Jacco Th.; Marshall, Jonathan R.; Matsuura, Mikako; Zijlstra, Albert A.

    2003-06-01

    LI-LMC 1813 is a dust-enshrouded asymptotic giant branch (AGB) star, located in the small open cluster KMHK 1603 near the rim of the Large Magellanic Cloud (LMC). Optical and infrared photometry between 0.5 and 60 μm is obtained to constrain the spectral energy distribution of LI-LMC 1813. Near-infrared spectra unambiguously show it to be a carbon star. Modelling with the radiation transfer code DUSTY yields accurate values for the bolometric luminosity, L= 1.5 × 104 Lsolar, and mass-loss rate, . On the basis of colour-magnitude diagrams, the age of the cluster KMHK 1603 is estimated to be t= 0.9-1.0 Gyr, which implies a zero-age main-sequence mass for LI-LMC 1813 of MZAMS= 2.2 +/- 0.1 Msolar. This makes LI-LMC 1813 arguably the object with the most accurately and reliably determined (circum)stellar parameters amongst all carbon stars in the superwind phase.

  10. Dust-driven winds of AGB stars: The critical interplay of atmospheric shocks and luminosity variations

    NASA Astrophysics Data System (ADS)

    Liljegren, S.; Höfner, S.; Nowotny, W.; Eriksson, K.

    2016-04-01

    Context. Winds of AGB stars are thought to be driven by a combination of pulsation-induced shock waves and radiation pressure on dust. In dynamic atmosphere and wind models, the stellar pulsation is often simulated by prescribing a simple sinusoidal variation in velocity and luminosity at the inner boundary of the model atmosphere. Aims: We experiment with different forms of the luminosity variation in order to assess the effects on the wind velocity and mass-loss rate, when progressing from the simple sinusoidal recipe towards more realistic descriptions. This will also give an indication of how robust the wind properties derived from the dynamic atmosphere models are. Methods: Using state-of-the-art dynamical models of C-rich AGB stars, a range of different asymmetric shapes of the luminosity variation and a range of phase shifts of the luminosity variation relative to the radial variation are tested. These tests are performed on two stellar atmosphere models. The first model has dust condensation and, as a consequence, a stellar wind is triggered, while the second model lacks both dust and wind. Results: The first model with dust and stellar wind is very sensitive to moderate changes in the luminosity variation. There is a complex relationship between the luminosity minimum, and dust condensation: changing the phase corresponding to minimum luminosity can either increase or decrease mass-loss rate and wind velocity. The luminosity maximum dominates the radiative pressure on the dust, which in turn, is important for driving the wind. An earlier occurrence of the maximum, with respect to the propagation of the pulsation-induced shock wave, then increases the wind velocity, while a later occurrence leads to a decrease. These effects of changed luminosity variation are coupled with the dust formation. In contrast there is very little change to the structure of the model without dust. Conclusions: Changing the luminosity variation, both by introducing a phase shift

  11. Dust-driven winds of AGB stars: The critical interplay of atmospheric shocks and luminosity variations

    NASA Astrophysics Data System (ADS)

    Liljegren, S.; Höfner, S.; Nowotny, W.; Eriksson, K.

    2016-05-01

    Context. Winds of AGB stars are thought to be driven by a combination of pulsation-induced shock waves and radiation pressure on dust. In dynamic atmosphere and wind models, the stellar pulsation is often simulated by prescribing a simple sinusoidal variation in velocity and luminosity at the inner boundary of the model atmosphere. Aims: We experiment with different forms of the luminosity variation in order to assess the effects on the wind velocity and mass-loss rate, when progressing from the simple sinusoidal recipe towards more realistic descriptions. This will also give an indication of how robust the wind properties derived from the dynamic atmosphere models are. Methods: Using state-of-the-art dynamical models of C-rich AGB stars, a range of different asymmetric shapes of the luminosity variation and a range of phase shifts of the luminosity variation relative to the radial variation are tested. These tests are performed on two stellar atmosphere models. The first model has dust condensation and, as a consequence, a stellar wind is triggered, while the second model lacks both dust and wind. Results: The first model with dust and stellar wind is very sensitive to moderate changes in the luminosity variation. There is a complex relationship between the luminosity minimum, and dust condensation: changing the phase corresponding to minimum luminosity can either increase or decrease mass-loss rate and wind velocity. The luminosity maximum dominates the radiative pressure on the dust, which in turn, is important for driving the wind. An earlier occurrence of the maximum, with respect to the propagation of the pulsation-induced shock wave, then increases the wind velocity, while a later occurrence leads to a decrease. These effects of changed luminosity variation are coupled with the dust formation. In contrast there is very little change to the structure of the model without dust. Conclusions: Changing the luminosity variation, both by introducing a phase shift

  12. The composition of freshly-formed dust in recent (post-)AGB thermal pulses

    NASA Astrophysics Data System (ADS)

    Gandhi, Poshak

    2013-01-01

    We recently discovered a candidate Asymptotic Giant Branch (AGB) star undergoing a thermal pulse (TP). WISE J1810--3305 is one of only two sources in the WISE sky survey which show very red WISE colors but a very blue 2MASS [K] vs. WISE [W1 (3.4 mu m)] color, and drastic brightening at 12 mu m since IRAS observation. This favours a scenario in which we have caught a massive dust ejection event during a TP that began only ~15 years ago. The other source is Sakurai's object, which also underwent a massive dust expulsion around the same time, but is in a later evolutionary (post-AGB) phase. Few firm constraints exist on the TP stage because of its brevity. These objects provide a unique opportunity for understanding TP evolution and dust production in real-time. Here we propose COMICS spectroscopy of WISE J1810--3305 in order to study the composition of the circumstellar dust. We will search for molecular bands, and identify whether the central object is an Oxygen or Carbon rich AGB star. We also propose identical spectroscopy of Sakurai's object in order to compare AGB with post-AGB evolution. These objects are presently brightest in the mid-IR, and COMICS is the only ground-based mid-IR camera with the requisite capability for observation.

  13. Evolution of planetary systems with time-dependent stellar mass-loss

    NASA Astrophysics Data System (ADS)

    Adams, Fred C.; Anderson, Kassandra R.; Bloch, Anthony M.

    2013-06-01

    Observations indicate that intermediate-mass stars, binary stars and stellar remnants often host planets; a complete explanation of these systems requires an understanding of how planetary orbits evolve as their central stars lose mass. Motivated by these dynamical systems, this paper generalizes in two directions previous studies of orbital evolution in planetary systems with stellar mass-loss: (1) many previous treatments focus on constant mass-loss rates and much of this work is carried out numerically. Here, we study a class of single planet systems where the stellar mass-loss rate is time dependent. The mass-loss rate can be increasing or decreasing, but the stellar mass always decreases monotonically. For this class of models, we develop analytic approximations to specify the final orbital elements for planets that remain bound after the epoch of mass-loss, and find the conditions required for the planets to become unbound. We also show that for some mass-loss functions, planets become unbound only in the asymptotic limit where the stellar mass vanishes. (2) We consider the chaotic evolution for two planet systems with stellar mass-loss. Here, we focus on a model consisting of analogues of Jupiter, Saturn and the Sun. By monitoring the divergence of initially similar trajectories through time, we calculate the Lyapunov exponents of the system. This analogue Solar system is chaotic in the absence of mass-loss with Lyapunov time τly ≈ 5-10 Myr; we find that the Lyapunov time decreases with increasing stellar mass-loss rate, with a nearly linear relationship between the two time-scales. Taken together, the results of this paper help provide an explanation for a wide range of dynamical evolution that occurs in Solar systems with stellar mass-loss.

  14. VizieR Online Data Catalog: Obscured AGB in Magellanic Clouds. I. (Loup+ 1997)

    NASA Astrophysics Data System (ADS)

    Loup, C.; Zijlstra, A. A.; Waters, L. B. F. M.; Groenewegen, M. A. T.

    1997-02-01

    We have selected 198 IRAS sources in the Large Magellanic Cloud, and 11 in the Small Magellanic Cloud, which are the best candidates to be mass-loosing AGB stars (or possibly post-AGB stars). We used the catalogues of Schwering & Israel (1990, Cat. ) and Reid et al. (1990, Cat. ). They are based on the IRAS pointed observations and have lower detection limits than the Point Source Catalogue. We also made cross-identifications between IRAS sources and optical catalogues. (8 data files).

  15. Dust in the Early Universe and the Contribution of AGB Stars

    NASA Astrophysics Data System (ADS)

    Schneider, R.; Valiante, R.; Ventura, P.; dell'Agli, F.; di Criscienzo, M.

    2015-08-01

    We review the role of AGB stars in early dust enrichment in light of new theoretical dust yields for stars with mass 1-8 M⊙ and metallicity 3×10-4≥ Z ≥0.008, obtained with models that follow stellar evolution from the pre-main sequence phase until the almost complete ejection of the stellar mantle. The models have been shown to reproduce the measured dust production rates by carbon-rich and oxygen-rich AGB stars in the Small and Large Magellanic Clouds, as well as the observed colors of the so-called extreme stars in the LMC. We discuss the relative role of AGB stars and SNe in early dust enrichment and the impact of these two classes of stellar sources on the nature and composition of the first dust.

  16. Stringent limits on the ionized mass loss from A and F dwarfs

    SciTech Connect

    Brown, A.; Veale, A.; Judge, P.; Bookbinder, J.A.; Hubeny, I. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA High Altitude Observatory, Boulder, CO )

    1990-09-01

    Following the suggestion of Willson et al. (1987) that A- and F-type main-sequence stars might undergo significant mass loss due to pulsationally driven winds, upper limits to the ionized mass loss from A and F dwarfs have been obtained using VLA observations. These stringent upper limits show that the level of ionized mass loss would have at most only a small effect on stellar evolution. Radiative-equilibrium atmospheric and wind models for early A dwarfs indicate that it is highly likely that a wind flowing from such stars would be significantly ionized. In addition, late A and early F dwarfs exhibit chromospheric emission indicative of significant nonradiative heating. The present mass-loss limits are thus representative of the total mass-loss rates for these stars. It is concluded that A and F dwarfs are not losing sufficient mass to cause A dwarfs to evolve into G dwarfs. 24 refs.

  17. Stringent limits on the ionized mass loss from A and F dwarfs

    NASA Technical Reports Server (NTRS)

    Brown, Alexander; Veale, Anthony; Judge, Philip; Bookbinder, Jay A.; Hubeny, Ivan

    1990-01-01

    Following the suggestion of Willson et al. (1987) that A- and F-type main-sequence stars might undergo significant mass loss due to pulsationally driven winds, upper limits to the ionized mass loss from A and F dwarfs have been obtained using VLA observations. These stringent upper limits show that the level of ionized mass loss would have at most only a small effect on stellar evolution. Radiative-equilibrium atmospheric and wind models for early A dwarfs indicate that it is highly likely that a wind flowing from such stars would be significantly ionized. In addition, late A and early F dwarfs exhibit chromospheric emission indicative of significant nonradiative heating. The present mass-loss limits are thus representative of the total mass-loss rates for these stars. It is concluded that A and F dwarfs are not losing sufficient mass to cause A dwarfs to evolve into G dwarfs.

  18. Evolutionary Models of Super-Earths and Mini-Neptunes Incorporating Cooling and Mass Loss

    NASA Astrophysics Data System (ADS)

    Howe, Alex R.; Burrows, Adam

    2015-08-01

    We construct models of the structural evolution of super-Earth- and mini-Neptune-type exoplanets with H2-He envelopes, incorporating radiative cooling and XUV-driven mass loss. We conduct a parameter study of these models, focusing on initial mass, radius, and envelope mass fractions, as well as orbital distance, metallicity, and the specific prescription for mass loss. From these calculations, we investigate how the observed masses and radii of exoplanets today relate to the distribution of their initial conditions. Orbital distance and the initial envelope mass fraction are the most important factors determining planetary evolution, particularly radius evolution. Initial mass also becomes important below a “turnoff mass,” which varies with orbital distance, with mass-radius curves being approximately flat for higher masses. Initial radius is the least important parameter we study, with very little difference between the hot start and cold start limits after an age of 100 Myr. Model sets with no mass loss fail to produce results consistent with observations, but a plausible range of mass-loss scenarios is allowed. In addition, we present scenarios for the formation of the Kepler-11 planets. Our best fit to observations of Kepler-11b and Kepler-11c involves formation beyond the snow line, after which they moved inward, circularized, and underwent a reduced degree of mass loss.

  19. A stellar evolution paradigm based on specific mass loss and feedback modes

    NASA Technical Reports Server (NTRS)

    Cuntz, Manfred; Stencel, Robert E.

    1992-01-01

    We present a new paradigm for stellar evolution which deals with a detailed treatment of mass loss and feedback modes. The paradigm is presented as a logical diagram which describes the respective dependencies of atmospheric properties relevant to mass loss generation.

  20. The Compensation Committee. AGB Effective Committee Series

    ERIC Educational Resources Information Center

    Hyatt, Thomas K.

    2013-01-01

    This publication is part of an Association of Governing Boards of Universities and Colleges (AGB) series devoted to strengthening the role of key standing committees of governing boards. While there is no optimum committee system for institutions of higher education, certain principles, practices, and procedures prevail. The best practices…

  1. The Facilities Committee. AGB Effective Committee Series

    ERIC Educational Resources Information Center

    Kaiser, Harvey H.

    2012-01-01

    This publication is part of an Association of Governing Boards of Universities and Colleges (AGB) series devoted to strengthening the role of key standing committees of governing boards. While there is no optimum committee system for institutions of higher education, certain principles, practices, and procedures prevail. The best practices…

  2. 2011 AGB Survey of Higher Education Governance

    ERIC Educational Resources Information Center

    Association of Governing Boards of Universities and Colleges, 2011

    2011-01-01

    This report, the second of AGB's studies of higher education governance, documents the extent to which college and university boards are following good-governance practices. In addition, it takes a focused look at board engagement to determine the degree to which governing boards are actively, intellectually, and strategically involved with their…

  3. The Executive Committee. AGB Effective Committee Series

    ERIC Educational Resources Information Center

    Legon, Richard D.

    2012-01-01

    This publication is part of an Association of Governing Boards of Universities and Colleges (AGB) series devoted to strengthening the role of key standing committees of governing boards. While there is no optimum committee system for institutions of higher education, certain principles, practices, and procedures prevail. The best practices…

  4. The Audit Committee. AGB Effective Committee Series

    ERIC Educational Resources Information Center

    Staisloff, Richard L.

    2011-01-01

    This publication is part of an Association of Governing Boards of Universities and Colleges (AGB) series devoted to strengthening the role of key standing committees of governing boards. While there is no optimum committee system for institutions of higher education, certain principles, practices, and procedures prevail. The best practices…

  5. The Investment Committee. AGB Effective Committee Series

    ERIC Educational Resources Information Center

    Yoder, Jay A.

    2011-01-01

    This publication is part of an AGB series devoted to strengthening the role of key standing committees of governing boards. While there is no optimum committee system for institutions of higher education, certain principles, practices, and procedures prevail. The best practices included in this text support the objectives of board committees:…

  6. Mass-losing peculiar red giants - The comparison between theory and observations

    NASA Technical Reports Server (NTRS)

    Jura, M.

    1989-01-01

    The mass loss from evolved red giants is considered. It seems that red giants on the Asymptotic Giant Branch (AGB) are losing between 0.0003 and 0.0006 solar mass/sq kpc yr in the solar neighborhood. If all the main sequence stars between 1 and 5 solar masses ultimately evolve into white dwarfs with masses of 0.7 solar mass, the predicted mass loss rate in the solar neighborhood from these stars is 0.0008 solar mass/sq kpc yr. Although there are still uncertainties, it appears that there is no strong disagreement between theory and observation.

  7. New insights into the dust formation of oxygen-rich AGB stars

    NASA Astrophysics Data System (ADS)

    Karovicova, I.; Wittkowski, M.; Ohnaka, K.; Boboltz, D. A.; Fossat, E.; Scholz, M.

    2013-12-01

    the stellar surface at about 2 stellar radii, co-located with the extended atmosphere and SiO maser emission, and warm silicate grains at larger distances of about 4-5 stellar radii. We verified that the number densities of aluminum can match that of the best-fit Al2O3 dust shell near the inner dust radius in sufficiently extended atmospheres, confirming that Al2O3 grains can be seed particles for the further dust condensation. Together with literature data of the mass-loss rates, our sample is consistent with a hypothesis that stars with low mass-loss rates form primarily dust that preserves the spectral properties of Al2O3, and stars with higher mass-loss rate form dust with properties of warm silicates. Based on observations made with the Very Large Telescope Interferometer (VLTI) at the Paranal Observatory under program IDs 073.D-0711, 075.D-0097, 077.D-0630, 079.D-0172, and 082.D-0723.Tables 1-3, 8, 9 are available in electronic form at http://www.aanda.org

  8. AGB stars as a source of short-lived radioactive nuclei in the solar nebula

    NASA Technical Reports Server (NTRS)

    Wasserburg, G. J.; Gallino, R.; Busso, M.; Raiteri, C. M.

    1993-01-01

    The purpose is to estimate the possible contribution of some short-lived nuclei to the early solar nebula from asymptotic giant branch (AGB) sources. Low mass (1 to 3 solar mass) AGB stars appear to provide a site for synthesis of the main s process component for solar system material with an exponential distribution of neutron irradiations varies as exp(-tau/tau(sub 0)) (where tau is the time integrated neutron flux with a mean neutron exposure tau(sub 0)) for solar abundances with tau(sub 0) = 0.28 mb(sup -1). Previous workers estimated the synthesis of key short-lived nuclei which might be produced in AGB stars. While these calculations exhibit the basic characteristics of nuclei production by neutron exposure, there is need for a self-consistent calculation that follows AGB evolution and takes into account the net production from a star and dilution with the cloud medium. Many of the general approaches and the conclusions arrived at were presented earlier by Cameron. The production of nuclei for a star of 1.5 solar mass during the thermal pulsing of the AGB phase was evaluated. Calculations were done for a series of thermal pulses with tau(sub 0) = 0.12 and 0.28 mb(sup -1). These pulses involve s nucleosynthesis in the burning shell at the base of the He zone followed by the ignition of the H burning shell at the top of the He zone. After about 10-15 cycles the abundances of the various nuclei in the He zone become constant. Computations of the abundances of all nuclei in the He zone were made following Gallino. The mass of the solar nebula was considered to consist of some initial material of approximately solar composition plus some contributions from AGB stars. The ratios of the masses required from the AGB He burning zone to the ISM necessary to produce the observed value of Pd-107/Pd-108 in the early solar system were calculated and this dilution factor was applied to all other relevant nuclei.

  9. Research opportunities in loss of red blood cell mass in space flight

    NASA Technical Reports Server (NTRS)

    Talbot, J. M.; Fisher, K. D.

    1985-01-01

    Decreases of red blood cell mass and plasma volume have been observed consistently following manned space flights. Losses of red cell mass by United States astronauts have averaged 10 to 15% (range: 2 to 21%). Based on postflight estimates of total hemoglobin, Soviet cosmonauts engaged in space missions lasting from 1 to 7 months have exhibited somewhat greater losses. Restoration of red cell mass requires from 4 to 6 weeks following return to Earth, regardless of the duration of space flight.

  10. Population II stars and the Spite plateau. Stellar evolution models with mass loss

    NASA Astrophysics Data System (ADS)

    Vick, M.; Michaud, G.; Richer, J.; Richard, O.

    2013-04-01

    Aims: We aim to determine the constraints that observed chemical abundances put on the potential role of mass loss in metal poor dwarfs. Methods: Self-consistent stellar evolutionary models that include all the effects of atomic diffusion and radiative accelerations for 28 chemical species were computed for stellar masses between 0.6 and 0.8 M⊙. Models with an initial metallicity of Z0 = 0.00017 and mass loss rates from 10-15 M⊙ yr-1 to 10-12 M⊙ yr-1 were calculated. They were then compared to previous models with mass loss, as well as to models with turbulent mixing. Results: For models with an initial metallicity of [Fe/H]0 = -2.31, mass loss rates of about 10-12 M⊙ yr-1 lead to surface abundance profiles that are very similar to those obtained in models with turbulence. Both models have about the same level of agreement with observations of galactic-halo lithium abundances, as well as lithium and other elemental abundances from metal poor globular clusters such as NGC 6397. In this cluster, models with mass loss agree slightly better with subgiant observations of Li abundance than those with turbulence. Lower red giant branch stars instead favor the models with turbulence. Larger differences between models with mass loss and those with turbulence appear in the interior concentrations of metals. Conclusions: The relatively high mass loss rates required to reproduce plateau-like lithium abundances appear unlikely when compared to the solar mass-loss rate. However the presence of a chromosphere on these stars justifies further investigation of the mass-loss rates. Appendix A is available in electronic form at http://www.aanda.org

  11. The evolution of massive stars including mass loss - Presupernova models and explosion

    NASA Technical Reports Server (NTRS)

    Woosley, S. E.; Langer, Norbert; Weaver, Thomas A.

    1993-01-01

    The evolution of massive stars of 35, 40, 60, and 85 solar masses is followed through all stages of nuclear burning to the point of Fe core collapse. Critical nuclear reaction and mass-loss rates are varied. Efficient mass loss during the Wolf-Rayet (WR) stage is likely to lead to final masses as small as 4 solar masses. For a reasonable parameterization of the mass loss, there may be convergence of all WR stars, both single and in binaries, to a narrow band of small final masses. Our representative model, a 4.25 solar-mass WR presupernova derived from a 60 solar mass star, is followed through a simulated explosion, and its explosive nucleosynthesis and light curve are determined. Its properties are similar to those observed in Type Ib supernovae. The effects of the initial mass and mass loss on the presupernova structure of small mass WR models is also explored. Important properties of the presupernova star and its explosion can only be obtained by following the complete evolution starting on the main sequence.

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

    SciTech Connect

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

    2014-07-01

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

  13. OT2_jalcolea_2: Additional Hpoint observations of large post-AGB sources from HIFIStars

    NASA Astrophysics Data System (ADS)

    Alcolea, J.

    2011-09-01

    One of the most spectacular phases in the evolution of intermediate mass stars takes place at the end of their lives. At the end of the AGB, the central star dashes across the HR diagram from the red giant to the blue dwarf region. At the same time, the spherically symmetric and slowly expanding circumstellar envelopes around AGB stars become planetary nebulae (PNe), displaying a large variety of shapes and structures far more complex. This transformation takes place at the very end of the AGB, and it is due to the interaction of fast and bipolar molecular winds with the fossil AGB circumstellar envelope. The origin of these post-AGB winds is still unclear, but we know that the resulting two-wind interactions are only active during a very short period of time, ~ 100 yr, but still they are able to strongly modify the kinematics of the nebulae and re-shape them. To better understand these processes we must study the warm molecular gas component of early post-AGB sources, both pre-planetary nebulae (pPNe) and young PNe. Herschel/HIFI is very well suited at this, because its spectral coverage, high velocity resolution, and superb sensitivity. For these reasons, 10 pPNe and young PNe were included in the KPGT HIFISTARS, were a large number of spectral lines are observed in a moderate number of frequency setups, but just at the central point. In many cases this is simply enough, since most post-AGB sources in HIFIStars are compact. However there are three cases in which the non spherically symmetric structures seen in the warm gas are larger than the telescope beam: OH231.8+4.2, NGC7027 and NGC6302. Therefore we propose to perform some additional points in these three sources in a selected sample of HIFISTARS frequency setups, were we have detected strong lines of CO, H2O, NH3 and OH. These observations are crucial to understand the kinematics and interactions traced by these warm gas probes, and gain insight in the intricate problem of the post-AGB dynamics.

  14. Reconciling Change in Oi-Horizon 14C With Mass Loss for an Oak Forest

    SciTech Connect

    Hanson, P J; Swanston, C W; Garten, Jr., C T; Todd, D E; Trumbore, S E

    2005-06-27

    First-year litter decomposition was estimated for an upland-oak forest ecosystem using enrichment or dilution of the {sup 14}C-signature of the Oi-horizon. These isotopically-based mass-loss estimates were contrasted with measured mass-loss rates from past litterbag studies. Mass-loss derived from changes in the {sup 14}C-signature of the Oi-horizon suggested mean mass loss over 9 months of 45% which was higher than the corresponding 9-month rate extrapolated from litterbag studies ({approx}35%). Greater mass loss was expected from the isotopic approach because litterbags are known to limit mass loss processes driven by soil macrofauna (e.g., fragmentation and comminution). Although the {sup 14}C-isotope approach offers the advantage of being a non-invasive method, it exhibited high variability that undermined its utility as an alternative to routine litterbag mass loss methods. However, the {sup 14}C approach measures the residence time of C in the leaf litter, rather than the time it takes for leaves to disappear; hence radiocarbon measures are subject to C immobilization and recycling in the microbial pool, and do not necessarily reflect results from litterbag mass loss. The commonly applied two-compartment isotopic mixing model was appropriate for estimating decomposition from isotopic enrichment of near-background soils, but it produced divergent results for isotopic dilution of a multi-layered system with litter cohorts having independent {sup 14}C-signatures. This discrepancy suggests that cohort-based models are needed to adequately capture the complex processes involved in carbon transport associated with litter mass-loss. Such models will be crucial for predicting intra- and interannual differences in organic horizon decomposition driven by scenarios of climatic change.

  15. Reconciling Change in Oi-Horizon Carbon-14 with Mass Loss for an Oak Forest

    SciTech Connect

    Hanson, Paul J; Swanston, Christopher W.; Garten Jr, Charles T; Todd Jr, Donald E; Trumbore, Susan E.

    2005-01-01

    First-year litter decomposition was estimated for an upland-oak forest ecosystem using enrichment or dilution of the 14C-signature of the Oi-horizon. These isotopically-based mass-loss estimates were contrasted with measured mass-loss rates from past litterbag studies. Mass-loss derived from changes in the 14C-signature of the Oi-horizon suggested mean mass loss over 9 months of 45% which was higher than the corresponding 9-month rate extrapolated from litterbag studies (~35%). Greater mass loss was expected from the isotopic approach because litterbags are known to limit mass loss processes driven by soil macrofauna (e.g., fragmentation and comminution). Although the 14C-isotope approach offers the advantage of being a non-invasive method, it exhibited high variability that undermined its utility as an alternative to routine litterbag mass loss methods. However, the 14C approach measures the residence time of C in the leaf litter, rather than the time it takes for leaves to disappear; hence radiocarbon measures reflect C immobilization and recycling in the microbial pool, and do not necessarily replicate results from litterbag mass loss. The commonly applied two-compartment isotopic mixing model was appropriate for estimating decomposition from isotopic enrichment of near-background soils, but it produced divergent results for isotopic dilution of a multi-layered system with litter cohorts having independent 14C-signatures. This discrepancy suggests that cohort-based models are needed to adequately capture the complex processes involved in carbon transport associated with litter mass-loss. Such models will be crucial for predicting intra- and interannual differences in organic horizon decomposition driven by scenarios of climatic change.

  16. Exploring wind-driving dust species in cool luminous giants. III. Wind models for M-type AGB stars: dynamic and photometric properties

    NASA Astrophysics Data System (ADS)

    Bladh, S.; Höfner, S.; Aringer, B.; Eriksson, K.

    2015-03-01

    Context. Stellar winds observed in asymptotic giant branch (AGB) stars are usually attributed to a combination of stellar pulsations and radiation pressure on dust. Shock waves triggered by pulsations propagate through the atmosphere, compressing the gas and lifting it to cooler regions which creates favourable conditions for grain growth. If sufficient radiative acceleration is exerted on the newly formed grains through absorption or scattering of stellar photons, an outflow can be triggered. Strong candidates for wind-driving dust species in M-type AGB stars are magnesium silicates (Mg2SiO4 and MgSiO3). Such grains can form close to the stellar surface, they consist of abundant materials and, if they grow to sizes comparable to the wavelength of the stellar flux maximum, they experience strong acceleration by photon scattering. Aims: The purpose of this study is to investigate if photon scattering on Mg2SiO4 grains can produce realistic outflows for a wide range of stellar parameters in M-type AGB stars. Methods: We use a frequency-dependent radiation-hydrodynamics code with a detailed description for the growth of Mg2SiO4 grains to calculate the first extensive set of time-dependent wind models for M-type AGB stars. This set includes 139 solar-mass models, with three different luminosities (5000 L⊙, 7000 L⊙, and 10 000 L⊙) and effective temperatures ranging from 2600 K to 3200 K. The resulting wind properties, visual and near-IR photometry and mid-IR spectra are compared with observations. Results: We show that the models can produce outflows for a wide range of stellar parameters. We also demonstrate that they reproduce observed mass-loss rates and wind velocities, as well as visual and near-IR photometry. However, the current models do not show the characteristic silicate features at 10 and 18 μm as a result of the cool temperature of Mg2SiO4 grains in the wind. Including a small amount of Fe in the grains further out in the circumstellar envelope will

  17. Limits on detectability of mass loss from cool dwarfs

    NASA Technical Reports Server (NTRS)

    Mullan, D. J.; Doyle, J. G.; Redman, R. O.; Mathioudakis, M.

    1992-01-01

    Recent spectroscopic evidence supports the theoretical expectation that certain cool dwarfs may have stellar winds with M-dot values several orders of magnitude larger than the solar rate. For large enough values of M-dot, the emission from the wind is expected to have a spectrum which, at low enough frequencies, becomes a power law, S(v) about v exp alpha with alpha about 0.7. Data from IRAS and VLA suggest that such a spectrum may in fact occur in certain M dwarfs: a key test of the wind spectrum would be provided if the stars could be detected at lambda about 1 mm. We show that the M-dot required to ensure power-law emission is a few times 10 exp -10 solar mass/yr. With M-dot of this order, fluxes at lambda about 1 mm would be tens of mJy. Using the James Clerk Maxwell Telescope, we have tested this prediction on several stars: the data are suggestive but are near the limits of detection. Confirmation of our estimates will be important for evolution and for interstellar medium (ISM) physics: if even a few percent of all M dwarfs are losing mass at the above rates, the mass balance of the ISM will be dominated by M dwarfs.

  18. A study of the mass loss rates of symbiotic star systems

    NASA Astrophysics Data System (ADS)

    Korreck, K. E.; Kellogg, E.; Sokoloski, J. L.

    2007-08-01

    The amount of mass loss in symbiotic systems is investigated, specifically mass loss via the formation of jets in R Aquarii (R Aqr). The jets in R Aqr have been observed in the X-ray by Chandra over a four year time period. The jet changes on times scales of a year and new outflows have been observed. Understanding the amount of mass and the frequency of ejection further constrain the ability of the white dwarf in the system to accrete enough mass to become a Type 1a supernova progenitor. The details of multi-wavelength studies, such as speed, density and spatial extent of the jets will be discussed in order to understand the mass balance in the binary system. We examine other symbiotic systems to determine trends in mass loss in this class of objects.

  19. A Study of the Mass Loss Rates of Symbiotic Star Systems

    NASA Technical Reports Server (NTRS)

    Korreck, K. E.; Kellogg, E.; Sokoloski, J. L.

    2007-01-01

    The amount of mass loss in symbiotic systems is investigated, specifically mass loss via the formation of jets in R Aquarii (R Aqr). The jets in R Aqr have been observed in the X-ray by Chandra over a four year time period. The jet changes on times scales of a year and new outflows have been observed. Understanding the amount of mass and the frequency of ejection further constrain the ability of the white dwarf in the system to accrete enough mass to become a Type la supernova progenitor. The details of multi-wavelength studies, such as speed, density and spatial extent of the jets will be discussed in order to understand the mass balance in the binary system. We examine other symbiotic systems to determine trends in mass loss in this class of objects.

  20. The Wind and Mass-loss Properties of the Most Massive Stars

    NASA Astrophysics Data System (ADS)

    Bestenlehner, Joachim; Vink, Jorick; Gräfener, Götz; Najarro, Francisco

    2013-06-01

    Mass-loss rates play an important role in the evolution of massive stars. The initial, present day and the mass at their end of their lifetime is considerable different as a result of mass loss. Different stages of evolution have different mass-loss rates. The understanding of massive star evolution is tightly connected to the understanding of their mass loss properties. In the context of the VLT-Flames Tarantula Survey I will present the results from our spectral analysis of stars in the transition region from O-stars to very massive WN(h)-stars. WN(h)-stars are very young and massive stars which develop already in the earliest stages of their evolution WR-star like winds. For the analysis we used the non-LTE radiative transfer code CMFGEN to investigate the wind and mass-loss properties of these very massive stars. This analysis also tests theoretical predictions which suggest a notable change of the mass-loss behaviour at a certain Eddington factor in the transition region from O to WN(h)-stars (Bestenlehner et al. 2011, Bestenlehner et al. in prep.)

  1. Is dynamometry able to infer the risk of muscle mass loss in patients with COPD?

    PubMed Central

    Ramos, Dionei; Bertolini, Giovana Navarro; Leite, Marceli Rocha; Carvalho Junior, Luiz Carlos Soares; da Silva Pestana, Paula Roberta; dos Santos, Vanessa Ribeiro; Fortaleza, Ana Claudia de Souza; Rodrigues, Fernanda Maria Machado; Ramos, Ercy Mara Cipulo

    2015-01-01

    Introduction Sarcopenia is characterized by a progressive and generalized decrease of strength and muscle mass. Muscle mass loss is prevalent in patients with chronic obstructive pulmonary disease (COPD) as a result of both the disease and aging. Some methods have been proposed to assess body composition (and therefore identify muscle mass loss) in this population. Despite the high accuracy of some methods, they require sophisticated and costly equipment. Aim The purpose of this study was to infer the occurrence of muscle mass loss measured by a sophisticated method (dual energy X-ray absorptiometry [DEXA]) using a more simple and affordable equipment (dynamometer). Methods Fifty-seven stable subjects with COPD were evaluated for anthropometric characteristics, lung function, functional exercise capacity, body composition, and peripheral muscle strength. A binary logistic regression model verified whether knee-extension strength (measured by dynamometry) could infer muscle mass loss (from DEXA). Results Patients with decreased knee-extension strength were 5.93 times more likely to have muscle mass loss, regardless of sex, disease stage, and functional exercise capacity (P=0.045). Conclusion Knee-extension dynamometry was able to infer muscle mass loss in patients with COPD. PMID:26229459

  2. Evolved Late-Type Star FUV Spectra: Mass Loss and Fluorescence

    NASA Technical Reports Server (NTRS)

    Harper, Graham M.

    2005-01-01

    This proposal was for a detailed analysis of the far ultraviolet (FUV) photoionizing radiation that provides crucial input physics for mass loss studies, e.g., observations of the flux below 10448, allow us to constrain the Ca II/Ca III balance and make significant progress beyond previous optical studies on stellar mass loss and circumstellar photochemistry. Our targets selection provided good spectral-type coverage required to help unravel the Ca II/Ca III balance as the mass-loss rates increase by over three orders of magnitude from K5 III to M5 III. We also explored the relationship between the FUV radiation field and other UV diagnostics to allow us to empirically estimate the FUV radiation field for the vast majority of stars which are too faint to be observed with FUSE, and to improve upon their uncertain mass-loss rates.

  3. Observations and theory of mass loss in late-type stars

    NASA Technical Reports Server (NTRS)

    Hartmann, L.

    1981-01-01

    The presented review is mainly concerned with the ubiquitous mass loss which occurs during most of a star's existence as a cool giant or supergiant. Observations of mass loss are considered, taking into account wind components and kinematics, and the temperature structure of cool winds. Theories of mass loss are examined, giving attention to radiation pressure on dust, radiation pressure in Lyman alpha, and magnetic wave-driven winds. It is pointed out that the study of mass loss from late-type stars appears to be entering a promising new phase. In this phase, the behavior of cool giants and supergiants is considered from a solar perspective, a perspective which contains important implications concerning the nature of solar activity.

  4. Trajectory Simulation of Meteors Assuming Mass Loss and Fragmentation

    NASA Technical Reports Server (NTRS)

    Allen, Gary A., Jr.; Prabhu, Dinesh K.; Saunders, David A

    2015-01-01

    Program used to simulate atmospheric flight trajectories of entry capsules [1] Includes models of atmospheres of different planetary destinations - Earth, Mars, Venus, Jupiter, Saturn, Uranus, Titan, ... Solves 3-­-degrees of freedom (3DoF) equations for a single body treated as a point mass. Also supports 6-DoF trajectory simula4on and Monte Carlo analyses. Uses Fehlberg-­-Runge-­-Kuna (4th-5th order) time integraion with automaic step size control. Includes rotating spheroidal planet with gravitational field having a J2 harmonic. Includes a variety of engineering aerodynamic and heat flux models. Capable of specifying events - heatshield jettison, parachute deployment, etc. - at predefined altitudes or Mach number. Has material thermal response models of typical aerospace materials integrated.

  5. The use of body mass loss to estimate metabolic rate in birds.

    PubMed

    Portugal, Steven J; Guillemette, Magella

    2011-03-01

    During starvation, energy production occurs at the expense of body reserve utilisation which results in body mass loss. Knowing the role of the fuels involved in this body mass loss, along with their energy density, can allow an energy equivalent of mass loss to be calculated. Therefore, it is possible to determine daily energy expenditure (DEE) if two body mass loss measurements at an interval of a few days are obtained. The technique can be cheap, minimally stressful for the animals involved, and the data relatively simple to gather. Here we review the use of body mass loss to estimate DEE in birds through critiquing the strengths and weaknesses of the technique, and detail the methodology and considerations that must be adhered to for accurate measures of DEE to be obtained. Owing to the biology of the species, the use of the technique has been used predominantly in Antarctic seabirds, particularly penguins and albatrosses. We demonstrate how reliable the technique can be in predicting DEE in a non-Antarctic species, common eiders (Somateria mollissima), the female of which undergoes a fasting period during incubation. We conclude that using daily body mass loss to estimate DEE can be a useful and effective approach provided that (1) the substrate being consumed during mass loss is known, (2) the kinetics of body mass loss are understood for the species in question and (3) only species that enter a full phase II of a fast (where substrate catabolism reaches a steady state) and are not feeding for a period of time are appropriate for this method. PMID:21144908

  6. Equation of Motion of an Interstellar Bussard Ramjet with Radiation and Mass Losses

    ERIC Educational Resources Information Center

    Semay, Claude; Silvestre-Brac, Bernard

    2008-01-01

    An interstellar Bussard ramjet is a spaceship using the protons of the interstellar medium in a fusion engine to produce thrust. In recent papers, it was shown that the relativistic equation of motion of an ideal ramjet and that of a ramjet with radiation loss are analytical. When a mass loss appears, the limit speed of the ramjet is more strongly…

  7. Highly reduced mass loss rates and increased litter layer in radioactively contaminated areas.

    PubMed

    Mousseau, Timothy A; Milinevsky, Gennadi; Kenney-Hunt, Jane; Møller, Anders Pape

    2014-05-01

    The effects of radioactive contamination from Chernobyl on decomposition of plant material still remain unknown. We predicted that decomposition rate would be reduced in the most contaminated sites due to an absence or reduced densities of soil invertebrates. If microorganisms were the main agents responsible for decomposition, exclusion of large soil invertebrates should not affect decomposition. In September 2007 we deposited 572 bags with uncontaminated dry leaf litter from four species of trees in the leaf litter layer at 20 forest sites around Chernobyl that varied in background radiation by more than a factor 2,600. Approximately one quarter of these bags were made of a fine mesh that prevented access to litter by soil invertebrates. These bags were retrieved in June 2008, dried and weighed to estimate litter mass loss. Litter mass loss was 40% lower in the most contaminated sites relative to sites with a normal background radiation level for Ukraine. Similar reductions in litter mass loss were estimated for individual litter bags, litter bags at different sites, and differences between litter bags at pairs of neighboring sites differing in level of radioactive contamination. Litter mass loss was slightly greater in the presence of large soil invertebrates than in their absence. The thickness of the forest floor increased with the level of radiation and decreased with proportional loss of mass from all litter bags. These findings suggest that radioactive contamination has reduced the rate of litter mass loss, increased accumulation of litter, and affected growth conditions for plants. PMID:24590204

  8. Overwinter mass loss of snowshoe hares in the Yukon: starvation, stress, adaptation or artefact?

    PubMed

    Hodges, Karen E; Boonstra, Rudy; Krebs, Charles J

    2006-01-01

    1. Overwinter mass loss can reduce energetic requirements in mammals (Dehnel's phenomenon). Alternatively, mass loss can result from food limitation or high predation risk. 2. We use data from fertilizer, food-supplementation and predator-exclusion experiments in the Yukon during a population cycle from 1986 to 1996 to test the causes of overwinter mass loss by snowshoe hares (Lepus americanus). In all years, some hares on control sites gained mass overwinter. During the increase phase the majority gained mass, but in all other phases the majority lost mass. 3. Snowshoe hares weighing <1000 g in autumn always gained mass overwinter, as did the majority that weighed 1000-1400 g. Hares weighing >1800 g in autumn usually lost mass. 4. Snowshoe hares on the predator-exclosure + food site gained mass overwinter in all years. Hares on the food-supplementation sites lost mass during the decline but gained mass in all other phases. Fertilization had little effect on mass dynamics. 5. Snowshoe hares were more likely to lose mass during winters with low survival rates. Snowshoe hares on the predator-exclosure treatments were more likely to gain mass than were hares on control sites. 6. Overwinter mass loss was correlated with maximum snow depth. At equivalent snow depths, hares on food-supplemented areas lost 98 g (+/- 14.6 SE) less on average than hares on the controls and predator-exclosure treatment. 7. Bone-marrow fat was related to body mass and cause of death. Small hares had the lowest marrow fat. Hares killed by humans had higher marrow fat than those killed by predators; hares that simply died had the lowest marrow fat. Hares on food-supplemented sites had the highest kidney and marrow fat. 8. Overwinter-mass loss for snowshoe hares is explained interactively by winter conditions, food supply, predation risk and autumn mass. Some snowshoe hares lost mass overwinter in all years and on all treatments, suggesting that reducing body mass may facilitate survival

  9. High resolution spectroscopy of the hot post-AGB stars IRAS 13266-5551 (CPD-55 5588) and IRAS 17311-4924 (Hen3-1428)

    NASA Astrophysics Data System (ADS)

    Sarkar, G.; Parthasarathy, M.; Reddy, B. E.

    2005-03-01

    High resolution spectra covering the wavelength range 4900 Å to 8250 Å of the hot post-AGB stars IRAS 13266-5551 (CPD-55 5588) and IRAS 17311-4924 (Hen3-1428) reveal absorption lines of C II, N II, O II, Al III, Si III and Fe III and a rich emission line spectrum consisting of H I, He I, C II, N I, O I, Mg II, Al II, Si II, V I, Mn I, Fe III, [Fe II] and [Cr II]. The presence of [N II] and [O I] lines and absence of [O III] indicate low excitation nebulae around these stars. The components of Na I absorption lines indicate the presence of neutral circumstellar envelopes in addition to the low excitation nebulae around these two hot post-AGB stars. The Hα lines show P-Cygni profiles indicating ongoing post-AGB mass loss. From the absorption lines we derived heliocentric radial velocities of 65.31 ± 0.34 km s-1 and 27.55 ± 0.74 km s-1 for IRAS 13266-5551 and IRAS 17311-4924 respectively. The high Galactic latitude and large radial velocity of IRAS 13266-5551 indicate that it belongs to the old disk population. Preliminary estimates for the CNO abundances in IRAS 13266-5551 are obtained. Based on observations made with the Victor M. Blanco 4m telescope of the Cerro Tololo Inter-American Observatory, Chile. Appendices and Tables [see full text], [see full text], [see full text] and [see full text] are only available in electronic form at http://www.edpsciences.org

  10. Asymmetries in AGB Stars: New Results from Aperture Masking Techniques

    NASA Astrophysics Data System (ADS)

    Lykou, F.; Hron, J.; Paladini, C.; Zijlstra, A. A.; Tuthill, P. G.; Norris, B.; Lagadec, E.

    2015-08-01

    Recent studies have shown that the extended circumstellar envelopes of AGB stars are not always spherical in shape. Moreover, the majority of post-AGB stars exhibit highly aspherical shapes, such as bipolar nebulae and equatorial waists in the form of dusty and gaseous disks and/or tori. As such, one should expect that the origin of the morphological changes seen in later evolutionary stages can be traced during the AGB phase. We now present a study of AGB stars using aperture masking interferometry to resolve such aspherical structures.

  11. DUST PRODUCTION AND MASS LOSS IN THE GALACTIC GLOBULAR CLUSTER NGC 362

    SciTech Connect

    Boyer, Martha L.; Gordon, Karl D.; Meixner, Margaret; Sewilo, Marta; Shiao, Bernie; Whitney, Barbara; McDonald, Iain; Van Loon, Jacco Th.; Oliveira, Joana M.; Babler, Brian; Bracker, Steve; Meade, Marilyn; Block, Miwa; Engelbracht, Charles; Misselt, Karl; Hora, Joe; Indebetouw, Remy

    2009-11-01

    We investigate dust production and stellar mass loss in the Galactic globular cluster NGC 362. Due to its close proximity to the Small Magellanic Cloud (SMC), NGC 362 was imaged with the Infrared Array Camera and Multiband Imaging Photometer cameras onboard the Spitzer Space Telescope as part of the Surveying the Agents of Galaxy Evolution (SAGE-SMC) Spitzer Legacy program. We detect several cluster members near the tip of the red giant branch (RGB) that exhibit infrared excesses indicative of circumstellar dust and find that dust is not present in measurable quantities in stars below the tip of the RGB. We modeled the spectral energy distribution (SED) of the stars with the strongest IR excess and find a total cluster dust mass-loss rate of 3.0{sup +2.0}{sub -1.2} x 10{sup -9} M{sub sun} yr{sup -1}, corresponding to a gas mass-loss rate of 8.6{sup +5.6}{sub -3.4} x 10{sup -6} M{sub sun} yr{sup -1}, assuming [Fe/H] =-1.16. This mass loss is in addition to any dustless mass loss that is certainly occurring within the cluster. The two most extreme stars, variables V2 and V16, contribute up to 45% of the total cluster dust-traced mass loss. The SEDs of the more moderate stars indicate the presence of silicate dust, as expected for low-mass, low-metallicity stars. Surprisingly, the SED shapes of the stars with the strongest mass-loss rates appear to require the presence of amorphous carbon dust, possibly in combination with silicate dust, despite their oxygen-rich nature. These results corroborate our previous findings in omega Centauri.

  12. Impact of mass-loss on the evolution and pre-supernova properties of red supergiants

    NASA Astrophysics Data System (ADS)

    Meynet, G.; Chomienne, V.; Ekström, S.; Georgy, C.; Granada, A.; Groh, J.; Maeder, A.; Eggenberger, P.; Levesque, E.; Massey, P.

    2015-03-01

    Context. The post-main-sequence evolution of massive stars is very sensitive to many parameters of the stellar models. Key parameters are the mixing processes, the metallicity, the mass-loss rate, and the effect of a close companion. Aims: We study the change in the red supergiant (RSG) lifetimes, the tracks in the Hertzsprung-Russel diagram (HRD), the positions in this diagram of the pre-supernova progenitor and the structure of the stars at that time for various mass-loss rates during the RSG phase and for two different initial rotation velocities. Methods: Stellar models were computed with the Geneva code for initial masses between 9 and 25 M⊙ at solar metallicity (Z = 0.014) with 10 times and 25 times the standard mass-loss rates during the RSG phase, with and without rotation. Results: The surface abundances of RSGs are much more sensitive to rotation than to the mass-loss rates during that phase. A change of the RSG mass-loss rate has a strong impact on the RSG lifetimes and in turn on the luminosity function of RSGs. An observed RSG is associated with a model of higher initial mass when models with an enhanced RSG mass-loss rate are used to deduce that mass. At solar metallicity, models with an enhanced mass-loss rate produce significant changes in the populations of blue, yellow, and RSGs. When extended blue loops or blueward excursions are produced by enhanced mass-loss, the models predict that a majority of blue (yellow) supergiants are post-RSG objects. These post-RSG stars are predicted to show much lower surface rotational velocities than similar blue supergiants on their first crossing of the HR gap. Enhanced mass-loss rates during the RSG phase have little impact on the Wolf-Rayet populations. The position in the HRD of the end point of the evolution depends on the mass of the hydrogen envelope. More precisely, whenever at the pre-supernova stage the H-rich envelope contains more than about 5% of the initial mass, the star is a RSG, and whenever

  13. THE EFFECT OF MASS LOSS ON THE TIDAL EVOLUTION OF EXTRASOLAR PLANET

    SciTech Connect

    Guo, J. H.

    2010-04-01

    By combining mass loss and tidal evolution of close-in planets, we present a qualitative study on their tidal migrations. We incorporate mass loss in tidal evolution for planets with different masses and find that mass loss could interfere with tidal evolution. In an upper limit case (beta = 3), a significant portion of mass may be evaporated in a long evolution timescale. Evidence of greater modification of the planets with an initial separation of about 0.1 AU than those with a = 0.15 AU can be found in this model. With the assumption of a large initial eccentricity, the planets with initial mass <=1 M{sub J} and initial distance of about 0.1 AU could not survive. With the supposition of beta = 1.1, we find that the loss process has an effect on the planets with low mass at a {approx} 0.05 AU. In both cases, the effect of evaporation on massive planets can be neglected. Also, heating efficiency and initial eccentricity have significant influence on tidal evolution. We find that even low heating efficiency and initial eccentricity have a significant effect on tidal evolution. Our analysis shows that evaporation on planets with different initial masses can accelerate (decelerate) the tidal evolution due to the increase (decrease) in tide of the planet (star). Consequently, the effect of evaporation cannot be neglected in evolutionary calculations of close-in planets. The physical parameters of HD 209458b can be fitted by our model.

  14. Variable Stars and The Asymptotic Giant Branch: Stellar Pulsations, Dust Production, and Mass Loss

    NASA Astrophysics Data System (ADS)

    Speck, A. K.

    2014-09-01

    Low- and intermediate-mass stars (1-8 M⊙; LIMS) are very important contributors of material to the interstellar medium (ISM), and yet the mechanisms by which this matter is expelled remain a mystery. In this paper we discuss how interferometry plays a role in studying the interplay between pulsation, mass loss, dust formation, and evolution of these LIMS.

  15. Variable Stars and the Asymptotic Giant Branch: Stellar Pulsations, Dust Production, and Mass Loss

    NASA Astrophysics Data System (ADS)

    Speck, A. K.

    2012-06-01

    Low- and intermediate-mass stars (1-8 M⊙; LIMS) are very important contributors of material to the interstellar medium (ISM), and yet the mechanisms by which this matter is expelled remain a mystery. In this paper we discuss how interferometry plays a role in studying the interplay between pulsation, mass loss, dust formation and evolution of these LIMS.

  16. Mass Loss of Larsen B Tributary Glaciers (Antarctic Peninsula) Unabated Since 2002

    NASA Technical Reports Server (NTRS)

    Berthier, Etienne; Scambos, Ted; Shuman, Christopher A.

    2012-01-01

    Ice mass loss continues at a high rate among the large glacier tributaries of the Larsen B Ice Shelf following its disintegration in 2002. We evaluate recent mass loss by mapping elevation changes between 2006 and 201011 using differencing of digital elevation models (DEMs). The measurement accuracy of these elevation changes is confirmed by a null test, subtracting DEMs acquired within a few weeks. The overall 2006201011 mass loss rate (9.0 2.1 Gt a-1) is similar to the 2001022006 rate (8.8 1.6 Gt a-1), derived using DEM differencing and laser altimetry. This unchanged overall loss masks a varying pattern of thinning and ice loss for individual glacier basins. On Crane Glacier, the thinning pulse, initially greatest near the calving front, is now broadening and migrating upstream. The largest losses are now observed for the HektoriaGreen glacier basin, having increased by 33 since 2006. Our method has enabled us to resolve large residual uncertainties in the Larsen B sector and confirm its state of ongoing rapid mass loss.

  17. CO thermal emissions and mass loss of red-supergiants beyond the Milky Way

    NASA Astrophysics Data System (ADS)

    Matsuura, Mikako; Sargent, Benjamin; Yates, J.; Swinyard, B.; Royer, P.; Boyer, M.; Barlow, M. J.; Meixner, Margaret; Katrien Els Decin, Leen; Khouri, T.; van Loon, J.; Woods, P.

    2015-08-01

    It is crucial for understanding stellar evolution to study how red-supergiants lose their mass. Although mass loss of red-supergiants has been well studied in the Milky Way, it is poorly studied beyond the Milky Way. Particularly, galaxies have wide range of metallicities, and the key question is how metallicity affects dust formation in red-supergiants, hence, how dust-driven mass-loss could be affected by the metallicity. Theory predicted that mass loss rate is lower at low metallicity. Testing this hypothesis, we observed CO thermal emission lines in red-supergiants in the Large Magellanic Cloud, using the Herschel Space Observatory. These are the first detections of rotational CO lines from red-supergiants beyond the Milky Way. Although the metallicity of the Large Magellanic Cloud is about the half of the solar metallicity, no obvious metallicity effect was found on the gas mass-loss rate. The key parameter for the mass-loss rate is the luminosity of the star.

  18. Stability analysis, non-linear pulsations and mass loss of models for 55 Cygni (HD 198478)

    NASA Astrophysics Data System (ADS)

    Yadav, Abhay Pratap; Glatzel, Wolfgang

    2016-04-01

    55 Cygni is a variable supergiant. Recent observational studies revealed that this star pulsates in pressure, gravity and strange modes. The pulsations seem to be associated with episodes of mass loss. In this paper we present a theoretical study of stellar models with parameters close to that of 55 Cygni. A linear non-adiabatic stability analysis with respect to radial perturbations is performed and the evolution of instabilities into the non-linear regime is followed by numerical simulation. Our study indicates that the mass of 55 Cygni lies below 28 M⊙. As the final consequence of the instabilities the non-linear simulations revealed finite amplitude pulsations with periods consistent with the observations. The non-linear results also indicate a connection between pulsations and mass loss and allow for an estimate of the mean mass-loss rate. It is consistent with the observed values.

  19. Circumstellar CO Emission in S Stars I. Mass-Loss with Little or No Dust

    NASA Technical Reports Server (NTRS)

    Sahai, R.; Liechti, S.

    1994-01-01

    47 S stars have been searched for circumstellar CO (J=1-0 and/or 2-1) emission, and 29 have been detected, including 4 which show no evidence of dust in their IRAS LRS spectra and one with possibly no Tc (and therefore not an AGB star).

  20. A rat resistance exercise regimen attenuates losses of musculoskeletal mass during hindlimb suspension.

    PubMed

    Fluckey, J D; Dupont-Versteegden, E E; Montague, D C; Knox, M; Tesch, P; Peterson, C A; Gaddy-Kurten, D

    2002-12-01

    Exposure to microgravity and/or spaceflight causes dramatic losses in both muscle and bone mass. In normal gravity, resistance exercise has been effectively used to increase muscle and bone mass. We tested a novel form of resistance exercise training using flywheel technology as a countermeasure to offset the loss of musculoskeletal mass during 4 weeks of adult rat hindlimb suspension (HS), an unloading model of microgravity. Male, Sprague-Dawley rats (6-month old) were operantly conditioned to perform resistance exercise, and then randomly assigned to groups of sedentary control (CON), HS, and HS with resistance exercise training (HSRT; 2 sets of approximately 21 repetitions, 3 days week(-1) for 4 weeks during suspension). In soleus, HS resulted in lower (P < 0.05) muscle mass to body mass ratio (approximately 50% of controls) and rates of protein synthesis. HSRT significantly attenuated the loss of muscle mass in soleus muscle, and rates of protein synthesis for soleus were similar for HSRT and controls. There were no differences among groups for mass or rates of protein synthesis in extensor digitorum longus. In cancellous regions of the distal femur, HS resulted in significant reductions of bone mineral density (BMD), but this was restored to control levels with HSRT. Cortical regions of the femur were not different among HS, HSRT or control groups. Together, these data suggest that resistance training using flywheel technology may be a promising tool to attenuate losses of the musculoskeletal system during periods of hindlimb unloading. PMID:12444935

  1. Antarctic Mass Loss from GRACE from Space- and Time-Resolved Modeling with Slepian Functions

    NASA Astrophysics Data System (ADS)

    Simons, F. J.; Harig, C.

    2013-12-01

    The melting of polar ice sheets is a major contributor to global sea-level rise. Antarctica is of particular interest since most of the mass loss has occurred in West Antarctica, however updated glacial isostatic adjustment (GIA) models and recent mass gains in East Antarctica have reduced the continent-wide integrated decadal trend of mass loss. Here we present a spatially and temporally resolved estimation of the Antarctic ice mass change using Slepian localization functions. With a Slepian basis specifically for Antarctica, the basis functions maximize their energy on the continent and we can project the geopotential fields into a sparse set of orthogonal coefficients. By fitting polynomial functions to the limited basis coefficients we maximize signal-to-noise levels and need not perform smoothing or destriping filters common to other approaches. In addition we determine an empirical noise covariance matrix from the GRACE data to estimate the uncertainty of mass estimation. When applied to large ice sheets, as in our own recent Greenland work, this technique is able to resolve both the overall continental integrated mass trend, as well as the spatial distribution of the mass changes over time. Using CSR-RL05 GRACE data between Jan. 2003 and Jan 2013, we estimate the regional accelerations in mass change for several sub-regions and examine how the spatial pattern of mass has changed. The Amundsen Sea coast of West Antarctica has experienced a large acceleration in mass loss (-26 Gt/yr^2). While mass loss is concentrated near Pine Island and Thwaites glaciers, it has also increased along the coast further towards the Ross ice shelf.

  2. Mass Loss of Glaciers and Ice Caps From GRACE During 2002-2015

    NASA Astrophysics Data System (ADS)

    Ciraci, E.; Velicogna, I.; Wahr, J. M.; Swenson, S. C.

    2015-12-01

    We use time series of time-variable gravity from the NASA/DLR GRACE mission using a mascon approach to estimate the ice mass balance of the Earth's Mountain Glaciers and Ice Caps (GICs), excluding the Antarctic and the Greenland peripheral glaciers, between January 2003 and October 2014. We estimate a total ice mass loss equal to -217 ± 33 Gt/yr, equivalent to a sea level rise of 0.6±0.09 mm/yr. The global signal is driven by a few regions, contributing to almost of 75% of the total ice mass loss. Among these areas, the main contributor is the Canadian Arctic Archipelago with a total mass loss of -75 ± 9 Gt/yr, followed by Alaska (-51 ± 10 Gt/yr), Patagonia (-26 ± 10 Gt/yr) and the High Mountains of Asia (-25 ± 13 Gt/yr). The mass loss for most of the arctic regions is not constant, but accelerates with time. The Canadian Archipelago, in particular, undergoes a strong acceleration in mass waste (-7±1 Gt/yr2). The signal acceleration is mainly driven by the northern located Queen Elisabeth Islands (-4.5 ± 0.6 Gt/yr2). A similar behavior is observed for Svalbard and the Russian Arctic. In this second case, however, we observe an enhanced mass loss starting from the second decade of the 21st century after a period of nearly stable mass balance. The observed acceleration helps reconcile regional ice mass estimates obtained for different time periods.

  3. EVOLUTION OF PLANETARY ORBITS WITH STELLAR MASS LOSS AND TIDAL DISSIPATION

    SciTech Connect

    Adams, Fred C.; Bloch, Anthony M.

    2013-11-10

    Intermediate mass stars and stellar remnants often host planets, and these dynamical systems evolve because of mass loss and tides. This paper considers the combined action of stellar mass loss and tidal dissipation on planetary orbits in order to determine the conditions required for planetary survival. Stellar mass loss is included using a so-called Jeans model, described by a dimensionless mass loss rate γ and an index β. We use an analogous prescription to model tidal effects, described here by a dimensionless dissipation rate Γ and two indices (q, p). The initial conditions are determined by the starting value of angular momentum parameter η{sub 0} (equivalently, the initial eccentricity) and the phase θ of the orbit. Within the context of this model, we derive an analytic formula for the critical dissipation rate Γ, which marks the boundary between orbits that spiral outward due to stellar mass loss and those that spiral inward due to tidal dissipation. This analytic result Γ = Γ(γ, β, q, p, η{sub 0}, θ) is essentially exact for initially circular orbits and holds to within an accuracy of ≈50% over the entire multi-dimensional parameter space, where the individual parameters vary by several orders of magnitude. For stars that experience mass loss, the stellar radius often displays quasi-periodic variations, which produce corresponding variations in tidal forcing; we generalize the calculation to include such pulsations using a semi-analytic treatment that holds to the same accuracy as the non-pulsating case. These results can be used in many applications, e.g., to predict/constrain properties of planetary systems orbiting white dwarfs.

  4. On the Birth Masses of the Ancient Globular Clusters

    NASA Astrophysics Data System (ADS)

    Conroy, Charlie

    2012-10-01

    All globular clusters (GCs) studied to date show evidence for internal (star-to-star) variation in their light-element abundances (including Li, C, N, O, F, Na, Mg, Al, and probably He). These variations have been interpreted as evidence for multiple star formation episodes within GCs, with secondary episodes fueled, at least in part, by the ejecta of asymptotic giant branch (AGB) stars from a first generation of stars. A major puzzle emerging from this otherwise plausible scenario is that the fraction of stars associated with the second episode of star formation is observed to be much larger than expected for a standard initial mass function. The present work investigates this tension by modeling the observed anti-correlation between [Na/Fe] and [O/Fe] for 20 Galactic GCs. If the abundance pattern of the retained AGB ejecta does not depend on GC mass at fixed [Fe/H], then a strong correlation is found between the fraction of current GC stellar mass composed of pure AGB ejecta, fp , and GC mass. This fraction varies from 0.20 at low masses (104.5 M ⊙) to 0.45 at high masses (106.5 M ⊙). The fraction of mass associated with pure AGB ejecta is directly related to the total mass of the cluster at birth; the ratio between the initial and present mass in stars can therefore be derived. Assuming a star formation efficiency of 50%, the observed Na-O anti-correlations imply that GCs were at least 10-20 times more massive at birth, a conclusion that is in qualitative agreement with previous work. These factors are lower limits because any mass-loss mechanism that removes first- and second-generation stars equally will leave fp unchanged. The mass dependence of fp probably arises because lower mass GCs are unable to retain all of the AGB ejecta from the first stellar generation. Recent observations of elemental abundances in intermediate-age Large Magellanic Cloud clusters are re-interpreted and shown to be consistent with this basic scenario. The small scatter in fp at

  5. ON THE BIRTH MASSES OF THE ANCIENT GLOBULAR CLUSTERS

    SciTech Connect

    Conroy, Charlie

    2012-10-10

    All globular clusters (GCs) studied to date show evidence for internal (star-to-star) variation in their light-element abundances (including Li, C, N, O, F, Na, Mg, Al, and probably He). These variations have been interpreted as evidence for multiple star formation episodes within GCs, with secondary episodes fueled, at least in part, by the ejecta of asymptotic giant branch (AGB) stars from a first generation of stars. A major puzzle emerging from this otherwise plausible scenario is that the fraction of stars associated with the second episode of star formation is observed to be much larger than expected for a standard initial mass function. The present work investigates this tension by modeling the observed anti-correlation between [Na/Fe] and [O/Fe] for 20 Galactic GCs. If the abundance pattern of the retained AGB ejecta does not depend on GC mass at fixed [Fe/H], then a strong correlation is found between the fraction of current GC stellar mass composed of pure AGB ejecta, f{sub p} , and GC mass. This fraction varies from 0.20 at low masses (10{sup 4.5} M{sub Sun }) to 0.45 at high masses (10{sup 6.5} M{sub Sun }). The fraction of mass associated with pure AGB ejecta is directly related to the total mass of the cluster at birth; the ratio between the initial and present mass in stars can therefore be derived. Assuming a star formation efficiency of 50%, the observed Na-O anti-correlations imply that GCs were at least 10-20 times more massive at birth, a conclusion that is in qualitative agreement with previous work. These factors are lower limits because any mass-loss mechanism that removes first- and second-generation stars equally will leave f{sub p} unchanged. The mass dependence of f{sub p} probably arises because lower mass GCs are unable to retain all of the AGB ejecta from the first stellar generation. Recent observations of elemental abundances in intermediate-age Large Magellanic Cloud clusters are re-interpreted and shown to be consistent with this

  6. The 2014 AGB Survey of Higher Education Governance

    ERIC Educational Resources Information Center

    Hodge-Clark, Kristen

    2014-01-01

    "The 2014 AGB Survey of Higher Education Governance" is the fourth in AGB's studies of college and university governance. This report, based on survey responses from 592 public and independent boards, addresses a range of important governance topics that are receiving attention from boards and the news media, including presidential…

  7. Continuum-driven versus line-driven mass loss and the Eddington limit

    NASA Astrophysics Data System (ADS)

    Owocki, Stanley P.

    2007-08-01

    Basic stellar structure dictates that stars of ˜ 100 M or more will be close to the Eddington limit, with luminosities in excess of 106 L, and radiation pressure contributing prominently to the support against gravity. Although it is formally possible to generate static structure models of even more massive stars, recent studies of dense clusters show there is a sharp cutoff at masses above ˜ 150 M. This talk examines the role of extreme mass loss is limiting the masses of stars, emphasizing in particular that continuum driving, possibly associated with structural instabilities of radiation dominated envelope, can lead to much stronger mass loss than is possible by the usual line-scattering mechanism of steady stellar winds. However, population studies of very young, dense stellar clusters now suggest quite strongly that there is a sharp cutoff at masses above ca. 150 M (see, e.g., the talk by Sally Oey, in this JD 05, p. 206). This is sometimes attributed to a mass limit on star formation by accretion processes, though there are competing formation scenarios by binary or cluster merging that would seem likely to lead to formation of even higher mass stars (see talks in JD14 and S237). So given the above rough coincidence of the observational upper mass limit with the Eddington-limit domain of radiation-pressure dominance, it seems associated instabilities in stellar structure might actually be a more important factor in this upper mass limit, leading to extreme mass loss in LBV and/or giant eruption events, much as inferred from circumstellar nebulae observed around high mass stars like eta Carinae and the Pistol star.

  8. Evaluation of the roughness and mass loss of the flowable composites after simulated toothbrushing abrasion.

    PubMed

    Garcia, Fernanda Cristina Pimentel; Wang, Linda; D'Alpino, Paulo Henrique Perlatti; Souza, João Batista de; Araújo, Paulo Amarante de; Mondelli, Rafael Francisco de Lia

    2004-01-01

    The purpose of this study was to measure mass loss and surface roughness changes of different brands of flowable resin composites after a simulated toothbrushing test. The null hypotheses were that there would be no differences in mass loss and no significant changes in surface roughness after this test and that there would be no correlation between the two variables. The tested materials were Aeliteflo (Bisco), Flow-It (Pentron), Flow-It LF (Pentron), Natural Flow (DFL) and Wave (SDI). Z100 (3M/ESPE) microhybrid and Silux Plus (3M/ESPE) microfilled resin composites were used as control materials. Twelve specimens (5 mm in diameter, 3 mm thick) of each material were prepared according to manufacturers' instructions. Toothbrushing abrasion was performed on all specimens from each of the materials using a simulator. The percentage mass loss and surface roughness were assessed before and after 100,000 brushstrokes, using a Sartorius analytical balance of 0.0001 g accuracy and a Hommel Tester T1000, respectively. The measurements of both properties were statistically compared by paired t-test and Tukey's test (p < 0.05). All materials presented a statistically significant mass loss comparing initial and final values, with the exception of Flow-It LF. However, no difference was revealed when comparing the mass loss of the different tested materials. All materials became rougher and Wave presented statistically higher roughness compared to the other resin composites. Flowable resin composites did not seem to be superior to the control groups, and they can be expected to wear by mass loss and to have an increased roughness of surface after toothbrushing action. The anticipated null hypotheses were partially accepted. PMID:15311320

  9. VizieR Online Data Catalog: Adiabatic mass loss in binary stars. II. (Ge+, 2015)

    NASA Astrophysics Data System (ADS)

    Ge, H.; Webbink, R. F.; Chen, X.; Han, Z.

    2016-02-01

    In the limit of extremely rapid mass transfer, the response of a donor star in an interacting binary becomes asymptotically one of adiabatic expansion. We survey here adiabatic mass loss from Population I stars (Z=0.02) of mass 0.10M⊙-100M⊙ from the zero-age main sequence to the base of the giant branch, or to central hydrogen exhaustion for lower main sequence stars. The logarithmic derivatives of radius with respect to mass along adiabatic mass-loss sequences translate into critical mass ratios for runaway (dynamical timescale) mass transfer, evaluated here under the assumption of conservative mass transfer. For intermediate- and high-mass stars, dynamical mass transfer is preceded by an extended phase of thermal timescale mass transfer as the star is stripped of most of its envelope mass. The critical mass ratio qad (throughout this paper, we follow the convention of defining the binary mass ratio as q{equiv}Mdonor/Maccretor) above which this delayed dynamical instability occurs increases with advancing evolutionary age of the donor star, by ever-increasing factors for more massive donors. Most intermediate- or high-mass binaries with nondegenerate accretors probably evolve into contact before manifesting this instability. As they approach the base of the giant branch, however, and begin developing a convective envelope, qad plummets dramatically among intermediate-mass stars, to values of order unity, and a prompt dynamical instability occurs. Among low-mass stars, the prompt instability prevails throughout main sequence evolution, with qad declining with decreasing mass, and asymptotically approaching qad=2/3, appropriate to a classical isentropic n=3/2 polytrope. Our calculated qad values agree well with the behavior of time-dependent models by Chen & Han (2003MNRAS.341..662C) of intermediate-mass stars initiating mass transfer in the Hertzsprung gap. Application of our results to cataclysmic variables, as systems that must be stable against rapid mass

  10. Evolution models from the AGB to the PNe and the rapid evolution of SAO 244567

    NASA Astrophysics Data System (ADS)

    Lawlor, Timothy M.; Sebzda, Steven; Peterson, Zach

    2015-08-01

    We present evolution calculations from the Asymptotic Giant Branch (AGB) to the Planetary Nebula (PNe) phase for models of mass 1 M⊙ over a range of metallicities from primordial, Z = 10-14, through near solar, Z = 0.02. Using our grid of models, we determine a central star mass dependence on initial metallicity. We also present a range of low masses for our low to very low metal models. The understanding of these objects is an important part of galactic evolution and the evolution of the composition of the universe over a broad range of red shits. For our low Z models, we find key differences in how they cross the HR diagram to the PNe phase, compared with models with higher initial Z. Some of our models experience the so called AGB Final Thermal Pulse (AFTP), which is a helium pulse that occurs while leaving the AGB and causes a rapid looping evolution while evolving between the AGB and PN phase. We use these models to make comparisons to the central star of the Stingray Nebula, SAO 244567. This object has been observed to be rapidly evolving (heating) over more than the last 50 years and is the central star of the youngest known planetary nebula. These two characteristics are similar to what is expected for AFTP models. It is a short lived phase that is related to, but different than, very late thermal pulse objects such as Sakurai’s Object, FG Sge, and V605 Aql. These objects experienced a similar thermal pulse, but later on the white dwarf cooling track.

  11. Onset of rapid mass loss in cool giant stars - Magnetic field effects

    NASA Technical Reports Server (NTRS)

    Mullan, D. J.

    1982-01-01

    The possibility that closed magnetic field loops exist in steady state in stellar atmospheres in the HR diagram is examined. A model derived by Pneuman (1968) for helmet streamers in the solar corona is applied using a semi-empirical technique, to find that long-lived closed loops exist only below a certain boundary in the HR diagram. The region below this boundary is occupied by stars which are known to have hot coronae and slow mass loss. It is suggested that rapid mass loss sets in when closed field loops can no longer exist in steady state in the atmosphere.

  12. Excess mechanical loss associated with dielectric mirror coatings on test masses in interferometric gravitational wave detectors

    NASA Astrophysics Data System (ADS)

    Crooks, D. R. M.; Sneddon, P.; Cagnoli, G.; Hough, J.; Rowan, S.; Fejer, M. M.; Gustafson, E.; Route, R.; Nakagawa, N.; Coyne, D.; Harry, G. M.; Gretarsson, A. M.

    2002-03-01

    Interferometric gravitational wave detectors use mirrors whose substrates are formed from materials of low intrinsic mechanical dissipation. The two most likely choices for the test masses in future advanced detectors are fused silica or sapphire (Rowan S et al 2000 Phys. Lett. A 265 5). These test masses must be coated to form mirrors, highly reflecting at 1064 nm. We have measured the excess mechanical losses associated with adding dielectric coatings to substrates of fused silica and calculated the effect of the excess loss on the thermal noise in an advanced interferometer.

  13. Mass loss rates of uranium-zirconium carbide in flowing hydrogen and hydrogen-hydrocarbon mixtures

    NASA Astrophysics Data System (ADS)

    MacMillan, Donald P.

    1991-01-01

    The results of experimental determinations of mass loss rates from (U,Zr)C exposed to flowing hydrogen at high temperature are reported. Two experimental techniques were used: isothermal heating of samples by arc jet and heating of long, porous, tubular samples by electrical self-resistance. Total mass losses as high as 20% were obtained, and the composition of the residue was determined. The results of these experiments were encouraging and led to the decision to use (U,Zr)C fuel elements in the next test reactor, Nuclear Furnace 2.

  14. Microwave continuum measurements and estimates of mass loss rates for cool giants and supergiants

    NASA Technical Reports Server (NTRS)

    Drake, S. A.; Linsky, J. L.

    1986-01-01

    Attention is given to the results of a sensitive, 6-cm radio continuum survey conducted with the NRAO VLA of 39 of the nearest single cool giants and supergiants of G0-M5 spectral types; the survey was conducted in order to obtain accurate measurements of the mass loss rates of ionized gas for a representative sample of such stars, in order to furnish constraints for, and a better understanding of, the total mass loss rates. The inferred angular diameters for the cool giant sources are noted to be twice as large as photospheric angular diameters, implying that these stars are surrounded by extended chromospheres containing warm partially ionized gas.

  15. Mass Loss from Hypergiant Stars: Searching for Cool Dust in the Near-to-Mid IR

    NASA Astrophysics Data System (ADS)

    Shenoy, Dinesh; Humphreys, Roberta M.; Jones, Terry Jay; Marengo, Massimo; Gehrz, Robert D.; Helton, L. Andrew

    2015-01-01

    The final fate of the most massive stars depends on their mass loss histories during their lifetimes. Hypergiant stars residing near the empircal upper limit of luminosity on the HR Diagram shed mass during brief, intense periods of enhanced mass loss, with amounts as high as 10-3 M⊙ in a single event. Their circumstellar environments show extensive and complex ejecta at visual wavelengths. To further probe their mass-loss histories for evidence of earlier mass loss we have extended the search of hypergiants' circumstellar enviroments into the mid-to-far infrared for four famous objects: the yellow hypergiants IRC +10420 and rho Cas and the red hypergiants VY CMa and mu Ceph. We present high-resolution adaptive optics imaging from LBT/LMIRCam (2 - 5 µm) and MMT/MIRAC (8 - 12 µm), combined with recently obtained far-IR imaging from 11 - 37 µm obtained with SOFIA/FORCAST (Cycle 2). We also discuss their long wavelength SEDs.

  16. Mass Loss and Evolution of Stars and Star Clusters: a Personal Historical Perspective

    NASA Astrophysics Data System (ADS)

    Lamers, H. J. G. L. M.

    2008-06-01

    The development and progress of the studies of winds and mass loss from hot stars, from about 1965 up to now, is discussed in a personal historical perspective. The present state of knowledge about stellar winds, based on papers presented at this workshop, is described. About ten years ago the mechanisms of the winds were reasonably well understood, the mass loss rates were known, and the predictions of stellar evolution theory with mass loss agreed with observations. However, recent studies especially those based on FUSE observations, have resulted in a significant reduction of the mass loss rates, that disagrees with predictions from radiation driven wind models. The situation is discussed and future studies that can clarify the situation are suggested. I also discuss what is known about the dissolution of star clusters in different environments. The dissolution time can be derived from the mass and age distributions of cluster samples. The resulting dissolution times of clusters in the solar neighborhood (SN) and in interacting galaxies are shorter than predicted by two-body relaxation of clusters in a tidal field. Encounters with giant molecular clouds can explain the fate of clusters in the SN and are the most likely cause of the short lifetime of clusters in interacting galaxies.

  17. Synchrotron-Based in Situ Characterization of the Scaffold Mass Loss from Erosion Degradation.

    PubMed

    Bawolin, Nahshon K; Chen, Xiongbaio

    2016-01-01

    The mass loss behavior of degradable tissue scaffolds is critical to their lifespan and other degradation-related properties including mechanical strength and mass transport characteristics. This paper presents a novel method based on synchrotron imaging to characterize the scaffold mass loss from erosion degradation in situ, or without the need of extracting scaffolds once implanted. Specifically, the surface-eroding degradation of scaffolds in a degrading medium was monitored in situ by synchrotron-based imaging; and the time-dependent geometry of scaffolds captured by images was then employed to estimate their mass loss with time, based on the mathematical model that was adopted from the literature of surface erosion with the experimentally-identified model parameters. Acceptable agreement between experimental results and model predictions was observed for scaffolds in a cylindrical shape, made from poly(lactic-co-glycolic) acid (PLGA) and polycaprolactone (PCL). This study illustrates that geometry evaluation by synchrotron-based imaging is an effective means to in situ characterize the scaffold mass loss as well as possibly other degradation-related properties. PMID:27399789

  18. THE PERIOD CHANGE OF THE CEPHEID POLARIS SUGGESTS ENHANCED MASS LOSS

    SciTech Connect

    Neilson, Hilding R.; Langer, Norbert; Engle, Scott G.; Guinan, Ed; Wasatonic, Richard P.; Williams, David B.

    2012-02-15

    Polaris is one of the most observed stars in the night sky, with recorded observations spanning more than 200 years. From these observations, one can study the real-time evolution of Polaris via the secular rate of change of the pulsation period. However, the measurements of the rate of period change do not agree with predictions from state-of-the-art stellar evolution models. We show that this may imply that Polaris is currently losing mass at a rate of M-dot {approx}10{sup -6} M{sub Sun} yr{sup -1} based on the difference between modeled and observed rates of period change, consistent with pulsation-enhanced Cepheid mass loss. A relation between the rate of period change and mass loss has important implications for understanding stellar evolution and pulsation, and provides insight into the current Cepheid mass discrepancy.

  19. Mass loss as a driving mechanism of global tectonics of Enceladus

    NASA Astrophysics Data System (ADS)

    Czechowski, L.

    2015-10-01

    Enceladus, a satellite of Saturn, is the smallest celestial body in the Solar System where volcanic activity is observed. It is concentrated in the South Polar Terrain (SPT) where the mass is ejected into space with the rate ~200 kg/s. We suggest here the following tectonic consequences of this mass loss: subsidence of SPT, flow of matter in the mantle and motion of adjacent plates towards SPT. Some of these processes are modeled using numerical and laboratory simulations.

  20. High-resolution mapping of mass loss from highly evolved carbon stars

    NASA Technical Reports Server (NTRS)

    Ball, R.

    1986-01-01

    The molecular component of the mass outflow at high resolution was mapped with the Owens Valley Millimeter-Wave Interferometer in two well-known objects, CRL 2688 and CIT 6. Interferometric observations of a pair of carbon stars which are evolving toward the planetary nebula stage have revealed evidence of episodic, nonspherically symmetric mass loss, and may lead to a fuller understanding of shielding properties of the dust grains involved in these flows.

  1. Mass Balance of the Northern Antarctic Peninsula and its Ongoing Response to Ice Shelf Loss

    NASA Astrophysics Data System (ADS)

    Scambos, T. A.; Berthier, E.; Haran, T. M.; Shuman, C. A.; Cook, A. J.; Bohlander, J. A.

    2012-12-01

    An assessment of the most rapidly changing areas of the Antarctic Peninsula (north of 66°S) shows that ice mass loss for the region is dominated by areas affected by eastern-Peninsula ice shelf losses in the past 20 years. Little if any of the mass loss is compensated by increased snowfall in the northwestern or far northern areas. We combined satellite stereo-image DEM differencing and ICESat-derived along-track elevation changes to measure ice mass loss for the Antarctic Peninsula north of 66°S between 2001-2010, focusing on the ICESat-1 period of operation (2003-2009). This mapping includes all ice drainages affected by recent ice shelf loss in the northeastern Peninsula (Prince Gustav, Larsen Inlet, Larsen A, and Larsen B) as well as James Ross Island, Vega Island, Anvers Island, Brabant Island and the adjacent west-flowing glaciers. Polaris Glacier (feeding the Larsen Inlet, which collapsed in 1986) is an exception, and may have stabilized. Our method uses ASTER and SPOT-5 stereo-image DEMs to determine dh/dt for elevations below 800 m; at higher elevations ICESat along-track elevation differencing is used. To adjust along-track path offsets between its 2003-2009 campaigns, we use a recent DEM of the Peninsula to establish and correct for cross-track slope (Cook et al., 2012, doi:10.5194/essdd-5-365-2012; http://nsidc.org/data/nsidc-0516.html) . We reduce the effect of possible seasonal variations in elevation by using only integer-year repeats of the ICESat tracks for comparison. Mass losses are dominated by the major glaciers that had flowed into the Prince Gustav (Boydell, Sjorgren, Röhss), Larsen A (Edgeworth, Bombardier, Dinsmoor, Drygalski), and Larsen B (Hektoria, Jorum, and Crane) embayments. The pattern of mass loss emphasizes the significant and multi-decadal response to ice shelf loss. Areas with shelf losses occurring 30 to 100s of years ago seem to be relatively stable or losing mass only slowly (western glaciers, northernmost areas). The

  2. X-ray induced stellar mass loss near active galactic nuclei

    NASA Technical Reports Server (NTRS)

    Voit, G. Mark; Shull, J. Michael

    1988-01-01

    The effects of UV and X-ray radiation on stars in active galactic nuclei (AGN) are critically evaluated. Mass loss rates in X-ray-induced winds are evaluated for realistic red giant models, and the effects of the ablation of stellar envelopes by radiation pressure are considered. The importance of X-ray-induced mass loss in the standard quasar model is evaluated and whether it can provide a source of accretion fuel or emission-line clouds is discussed. It is concluded that thermal winds driven by X-ray heating are a minor total supply of mass to AGN, but that thermal plus line-driven winds and stellar ablation may increase the mass loss and improve the chances for supplying a fraction of the necessary mass supply to the central object. It is speculated that when steady winds are inefficient, complex time-dependent processes due to X-ray energy injection deep into a stellar atmosphere could still release significant mass from stars.

  3. On the formation of SMC X-1: The effect of mass and orbital angular momentum loss

    SciTech Connect

    Li, Tao; Li, X.-D. E-mail: lixd@nju.edu.cn

    2014-01-01

    SMC X-1 is a high-mass X-ray binary with an orbital period of 3.9 days. The mass of the neutron star is as low as ∼1M {sub ☉}, suggesting that it was likely formed through an electron-capture supernova rather than an iron-core collapse supernova. From the present system configurations, we argue that the orbital period at the supernova was ≲ 10 days. Since the mass transfer process between the neutron star's progenitor and the companion star before the supernova should have increased the orbital period to tens of days, a mechanism with efficient orbit angular momentum loss and relatively small mass loss is required to account for its current orbital period. We have calculated the evolution of the progenitor binary systems from zero-age main sequence to the pre-supernova stage with different initial parameters and various mass and angular momentum loss mechanisms. Our results show that the outflow from the outer Lagrangian point or a circumbinary disk formed during the mass transfer phase may be qualified for this purpose. We point out that these mechanisms may be popular in binary evolution and significantly affect the formation of compact star binaries.

  4. Effects of main-sequence mass loss on the turnoff ages of population 1 clusters

    SciTech Connect

    Guzik, J.A.

    1989-01-01

    Willson, Bowen, and Struck-Marcell have proposed that stars of spectral types A through early-G lose a significant portion of their mass during the early main-sequence phase. The proposed mass loss is driven by pulsation, and facilitated by rapid rotation. One implication of this hypothesis is that the main-sequence turnoff is an invalid indicator of cluster age, as present turnoff stars may have had higher projenitor masses; hence clusters appear older than they actually are. This paper presents examples of cluster HR diagrams synthesized with mass-losing stars of solar metallicity, initial masses 1-2 M/sub /circ dot//, and exponentially-decreasing mass-loss rates with e-folding times 1-2 Gyr. The increases in apparent turnoff age of Pop. I clusters, and the potential of the hypothesis to account for blue stragglers as normal stars that have not lost mass (or lost mass more slowly) are discussed. 9 refs., 6 figs.

  5. An ALMA View of the Complex Circumstellar Environment of the Post-AGB Object HD 101584

    NASA Astrophysics Data System (ADS)

    Olofsson, H.; Vlemmings, W.; Maercker, M.; Humphreys, E.; Lindqvist, M.; Nyman, L.; Ramstedt, S.

    2015-12-01

    We use 12CO, 13CO, and C18O J = 2-1 lines and 1.3 mm continuum ALMA observations to study the circumstellar evolution of the binary HD 101584, a post-AGB star and a low-mass companion, which is most likely a post-common-envelope-evolution system. It is inferred that the circumstellar medium has a bipolar hour-glass structure, seen almost pole-on, formed by an energetic, ≍ 150 km s-1, jet. Significant amount of material resides in an unresolved central region. It is proposed that the circumstellar morphology is related to an event which took place ≍ 500 yr ago, possibly a capture event where the companion spiraled in towards the AGB star. However, the kinetic energy of the accelerated gas exceeds the released orbital energy. Hence, the observed phenomenon does not match current common-envelope scenarios, and another process must augment, or even dominate, the ejection process.

  6. An ALMA view of the post-AGB object HD 101584

    NASA Astrophysics Data System (ADS)

    Olofsson, H.; Vlemmings, W.; Maercker, M.; Humphreys, E.; Lindqvist, M.; Nyman, L.; Ramstedt, S.

    2016-07-01

    ALMA cycles 1 and 3 observations of CO isotopologues and 1.3mm continuum are used in a study of the circumstellar environment of the binary HD 101584, a post-AGB star and a low-mass companion that is most likely a post-common-envelope-evolution system. These data are supplemented with new information from OH maser emission. It is inferred that the large- scale circumstellar medium has a bipolar hour-glass structure, seen almost pole-on, formed by an energetic, ≥⃒ 150 km s-1, jet. Significant amount of material still resides in the central region. It is proposed that the circumstellar morphology is related to an event which took place ≤⃒ 500 yr ago, possibly a capture event where the companion spiralled in towards the AGB star. Several observed features remain to be explained, and may hint to a more complicated scenario.

  7. Variability Studies in Two Hypergiants and a Post-AGB Object

    NASA Astrophysics Data System (ADS)

    Freund, Stephen; Hrivnak, Bruce J.; Lu, Wenxian

    2016-01-01

    In the course of long-term photometric monitoring of post-AGB stars at the Valparaiso University campus observatory, we have also observed some objects of uncertain evolutionary state. This includes two objects that have some of the characteristics of post-AGB stars, such as large IR excesses and F-G spectral types. The weight of recent evidence suggests that two of these, IRAS 19114+0002 (AFGL 2343) and IRAS 19244+1115 (IRC+10 420), are instead hypergiants, objects of very high luminosity arising from evolved high-mass progenitors. A third object, IRAS 20004+2955 (V1027 Cyg), appears to be a cool post-AGB star evolving from a low or intermediate-mass progenitor. We have light and color curves from 1994-2007, along with some radial velocity data from 1991-1995. These three objects display complex light and color curves with evidence of periodicity in the range of 100 to 300 days. We will present the results of these studies. This research is supported by grants from the National Science Foundation (most recently AST 1413660), the Indiana Space Grant Consortium, and Valparaiso University.

  8. Improving the distances of post-AGB objects in the Milky Way

    NASA Astrophysics Data System (ADS)

    Vickers, Shane B.; Frew, David J.; Owers, Matt S.; Parker, Quentin A.; Bojičič, Ivan S.

    2016-07-01

    Post-AGB (PAGB) stars are short-lived, low-intermediate mass objects transitioning from the asymptotic giant branch (AGB) to the white dwarf (WD) phase. These objects are characterised by a constant, core-mass dependent luminosity and a large infrared excess from the dusty envelope ejected at the top of the AGB. PAGB stars provide insights into the evolution of their direct descendants, planetary nebulae (PNe). Calculation of physical characteristics of PAGB are dependent on accurately determined distances scarcely available in the literature. Using the Torun catalogue for PAGB objects, supplemented with archival data, we have determined distances to the known population of Galactic PAGB stars. This is by modelling their spectral energy distributions (SED) with black bodies and numerically integrating over the entire wavelength range to determine the total integrated object flux. For most PAGB stars we assumed their luminosities are based on their positional characteristics and stellar evolution models. RV Tauri stars however are known to follow a period-luminosity relation (PLR) reminiscent of type-2 Cepheids. For these variable PAGB stars we determined their luminosities via the PLR and hence their distances. This allows us to overcome the biggest obstacle to characterising these poorly understood objects that play a vital part in Galactic chemical enrichment.

  9. The mass-loss return from evolved stars to the Large Magellanic Cloud. III. Dust properties for carbon-rich asymptotic giant branch stars

    NASA Astrophysics Data System (ADS)

    Srinivasan, S.; Sargent, B. A.; Matsuura, M.; Meixner, M.; Kemper, F.; Tielens, A. G. G. M.; Volk, K.; Speck, A. K.; Woods, P. M.; Gordon, K.; Marengo, M.; Sloan, G. C.

    2010-12-01

    We present a radiative transfer model for the circumstellar dust shell around a Large Magellanic Cloud (LMC) long-period variable (LPV) previously studied as part of the Optical Gravitational Lensing Experiment (OGLE) survey of the LMC. OGLE LMC LPV 28579 (SAGE J051306.40-690946.3) is a carbon-rich asymptotic giant branch (AGB) star for which we have Spitzer broadband photometry and spectra from the SAGE and SAGE-Spec programs along with broadband UBVIJHKs photometry. By modeling this source, we obtain a baseline set of dust properties to be used in the construction of a grid of models for carbon stars. We reproduce the spectral energy distribution of the source using a mixture of amorphous carbon and silicon carbide with 15% SiC by mass. The grain sizes are distributed according to the KMH model, with γ = 3.5, amin = 0.01 μm and a0 = 1.0 μm. The best-fit model produces an optical depth of 0.28 for the dust shell at the peak of the SiC feature (11.3 μm), with an inner radius of about 1430 R_⊙ or 4.4 times the stellar radius. The temperature at this inner radius is 1310 K. Assuming an expansion velocity of 10 km s-1, we obtain a dust mass-loss rate of 2.5 × 10-9 M_⊙ yr-1. We calculate a 15% variation in this mass-loss rate by testing the sensitivity of the fit to variation in the input parameters. We also present a simple model for the molecular gas in the extended atmosphere that could give rise to the 13.7 μm feature seen in the spectrum. We find that a combination of CO and C2H2 gas at an excitation temperature of about 1000 K and column densities of 3 × 1021 cm-2 and 1019 cm-2 respectively are able to reproduce the observations. Given that the excitation temperature is close to the temperature of the dust at the inner radius, most of the molecular contribution probably arises from this region. The luminosity corresponding to the first epoch of SAGE observations is 6580 L_⊙. For an effective temperature of about 3000 K, this implies a stellar mass of

  10. Support Loss and Q Factor Enhancement for a Rocking Mass Microgyroscope

    PubMed Central

    Wang, Xiong; Xiao, Dingbang; Zhou, Zelong; Wu, Xuezhong; Chen, Zhihua; Li, Shengyi

    2011-01-01

    A rocking mass gyroscope (RMG) is a kind of vibrating mass gyroscope with high sensitivity, whose driving mode and sensing mode are completely uniform. MEMS RMG devices are a research hotspot now because they have the potential to be used in space applications. Support loss is the dominant energy loss mechanism influencing their high sensitivity. An accurate analytical model of support loss for RMGs is presented to enhance their Q factors. The anchor type and support loss mechanism of an RMG are analyzed. Firstly, the support loads, powers flowing into support structure, and vibration energy of an RMG are all developed. Then the analytical model of support loss for the RMG is developed, and its sensitivities to the main structural parameters are also analyzed. High-Q design guidelines for rocking mass microgyroscopes are deduced. Finally, the analytical model is validated by the experimental data and the data from the existing literature. The thicknesses of the prototypes are reduced from 240 μm to 60 μm, while Q factors increase from less than 150 to more than 800. The derived model is general and applicable to various beam resonators, providing significant insight to the design of high-Q MEMS devices. PMID:22163727

  11. Stellar evolution including diffusion and matter flow induced by mass-loss

    NASA Astrophysics Data System (ADS)

    Richard, O.; Vick, M.

    2013-12-01

    It is clear that in order to explain many observed stellar phenomenae, atomic diffusion must be included in stellar models. Observed surface abundances allow us to constrain other transport pro- cesses which compete with atomic diffusion. We will focus on the effect of the flow of matter induced by mass-loss in stellar models.

  12. A survey of mass loss from Be and shell stars using ultraviolet data from Copernicus

    NASA Technical Reports Server (NTRS)

    Marlborough, J. M.; Snow, T. P., Jr.

    1976-01-01

    Ultraviolet spectra of intermediate resolution have been obtained with Copernicus of twelve objects classified as Be or shell stars, and an additional 19 dwarfs of spectral classes B0-B4. Some of these spectra show marked asymmetries in certain resonance lines, especially the Si IV doublet at 1400 A, indicating the presence of outflowing material with maximum velocities of nearly 1000 km/sec. Direct evidence for mass loss at these velocities is seen for the first time in dwarf stars as late as B1.5. Later than B0.5, the only survey objects showing this phenomenon are Be stars. Among the stars considered there is a correlation between the presence of mass-loss effects and projected rotational velocity, suggesting that the UV flux from B1-B3 dwarfs is sufficient to drive high-velocity stellar winds only if rotation reduces the effective gravity near the equator. The role of mass-loss in producing the Be star phenomenon and the effects of rotation on mass loss are discussed.

  13. The Influence of Mass Loss on the Eccentricity of Double Star Orbits

    NASA Astrophysics Data System (ADS)

    Docobo, J. A.; Prieto, C.; Ling, J. F.

    In this comunication we study the behaviour of the eccentricity of double star orbits (visual and wide spectroscopic binaries) according to simplified laws of mass loss. Applications to the systems WDS 05245S0224 - HD 35411, WDS 05387S0236 - HD 37468 and WDS 06154S0902 - HD 43362 are included.

  14. Evolved stars in the Local Group galaxies. I. AGB evolution and dust production in IC 1613

    NASA Astrophysics Data System (ADS)

    Dell'Agli, F.; Di Criscienzo, M.; Boyer, M. L.; García-Hernández, D. A.

    2016-05-01

    We used models of thermally-pulsing asymptotic giant branch (AGB) stars, that also describe the dust-formation process in the wind, to interpret the combination of near- and mid-infrared photometric data of the dwarf galaxy IC 1613. This is the first time that this approach is extended to an environment different from the Milky Way and the Magellanic Clouds (MCs). Our analysis, based on synthetic population techniques, shows a nice agreement between the observations and the expected distribution of stars in the colour-magnitude diagrams obtained with JHK and Spitzer bands. This allows a characterization of the individual stars in the AGB sample in terms of mass, chemical composition, and formation epoch of the progenitors. We identify the stars exhibiting the largest degree of obscuration as carbon stars evolving through the final AGB phases, descending from 1 - 1.25M⊙ objects of metallicity Z = 10-3 and from 1.5 - 2.5M⊙ stars with Z = 2 × 10-3. Oxygen-rich stars constitute the majority of the sample (˜65%), mainly low mass stars (<2M⊙) that produce a negligible amount of dust (≤10-7M⊙/yr). We predict the overall dust-production rate from IC 1613, mostly determined by carbon stars, to be ˜6 × 10-7M⊙/yr with an uncertainty of 30%. The capability of the current generation of models to interpret the AGB population in an environment different from the MCs opens the possibility to extend this kind of analysis to other Local Group galaxies.

  15. Evolved stars in the Local Group galaxies - I. AGB evolution and dust production in IC 1613

    NASA Astrophysics Data System (ADS)

    Dell'Agli, F.; Di Criscienzo, M.; Boyer, M. L.; García-Hernández, D. A.

    2016-08-01

    We used models of thermally pulsing asymptotic giant branch (AGB) stars, which also describe the dust-formation process in the wind, to interpret the combination of near- and mid-infrared photometric data of the dwarf galaxy IC 1613. This is the first time that this approach is extended to an environment different from the Milky Way and the Magellanic Clouds (MCs). Our analysis, based on synthetic population techniques, shows nice agreement between the observations and the expected distribution of stars in the colour-magnitude diagrams obtained with JHK and Spitzer bands. This allows a characterization of the individual stars in the AGB sample in terms of mass, chemical composition and formation epoch of the progenitors. We identify the stars exhibiting the largest degree of obscuration as carbon stars evolving through the final AGB phases, descending from 1-1.25 M⊙ objects of metallicity Z = 10-3 and from 1.5-2.5 M⊙ stars with Z = 2 × 10-3. Oxygen-rich stars constitute the majority of the sample (˜65 per cent), mainly low-mass stars (<2 M⊙) that produce a negligible amount of dust (≤10-7 M⊙ yr-1). We predict the overall dust-production rate from IC 1613, mostly determined by carbon stars, to be ˜6 × 10-7 M⊙ yr-1 with an uncertainty of 30 per cent. The capability of the current generation of models to interpret the AGB population in an environment different from the MCs opens the possibility to extend this kind of analysis to other Local Group galaxies.

  16. Evolved stars in the Local Group galaxies - I. AGB evolution and dust production in IC 1613

    NASA Astrophysics Data System (ADS)

    Dell'Agli, F.; Di Criscienzo, M.; Boyer, M. L.; García-Hernández, D. A.

    2016-08-01

    We used models of thermally-pulsing asymptotic giant branch (AGB) stars, that also describe the dust-formation process in the wind, to interpret the combination of near- and mid-infrared photometric data of the dwarf galaxy IC 1613. This is the first time that this approach is extended to an environment different from the Milky Way and the Magellanic Clouds (MCs). Our analysis, based on synthetic population techniques, shows a nice agreement between the observations and the expected distribution of stars in the colour-magnitude diagrams obtained with JHK and Spitzer bands. This allows a characterization of the individual stars in the AGB sample in terms of mass, chemical composition, and formation epoch of the progenitors. We identify the stars exhibiting the largest degree of obscuration as carbon stars evolving through the final AGB phases, descending from 1-1.25Msun objects of metallicity Z=0.001 and from 1.5-2.5Msun stars with Z=0.002. Oxygen-rich stars constitute the majority of the sample (65%), mainly low mass stars (<2Msun) that produce a negligible amount of dust (<10^{-7}Msun/yr). We predict the overall dust-production rate from IC 1613, mostly determined by carbon stars, to be 6x10^{-7}Msun/yr with an uncertainty of 30%. The capability of the current generation of models to interpret the AGB population in an environment different from the MCs opens the possibility to extend this kind of analysis to other Local Group galaxies.

  17. Constraints on the H2O formation mechanism in the wind of carbon-rich AGB stars

    NASA Astrophysics Data System (ADS)

    Lombaert, R.; Decin, L.; Royer, P.; de Koter, A.; Cox, N. L. J.; González-Alfonso, E.; Neufeld, D.; De Ridder, J.; Agúndez, M.; Blommaert, J. A. D. L.; Khouri, T.; Groenewegen, M. A. T.; Kerschbaum, F.; Cernicharo, J.; Vandenbussche, B.; Waelkens, C.

    2016-04-01

    Context. The recent detection of warm H2O vapor emission from the outflows of carbon-rich asymptotic giant branch (AGB) stars challenges the current understanding of circumstellar chemistry. Two mechanisms have been invoked to explain warm H2O vapor formation. In the first, periodic shocks passing through the medium immediately above the stellar surface lead to H2O formation. In the second, penetration of ultraviolet interstellar radiation through a clumpy circumstellar medium leads to the formation of H2O molecules in the intermediate wind. Aims: We aim to determine the properties of H2O emission for a sample of 18 carbon-rich AGB stars and subsequently constrain which of the above mechanisms provides the most likely warm H2O formation pathway. Methods: Using far-infrared spectra taken with the PACS instrument onboard the Herschel telescope, we combined two methods to identify H2O emission trends and interpreted these in terms of theoretically expected patterns in the H2O abundance. Through the use of line-strength ratios, we analyzed the correlation between the strength of H2O emission and the mass-loss rate of the objects, as well as the radial dependence of the H2O abundance in the circumstellar outflow per individual source. We computed a model grid to account for radiative-transfer effects in the line strengths. Results: We detect warm H2O emission close to or inside the wind acceleration zone of all sample stars, irrespective of their stellar or circumstellar properties. The predicted H2O abundances in carbon-rich environments are in the range of 10-6 up to 10-4 for Miras and semiregular-a objects, and cluster around 10-6 for semiregular-b objects. These predictions are up to three orders of magnitude greater than what is predicted by state-of-the-art chemical models. We find a negative correlation between the H2O/CO line-strength ratio and gas mass-loss rate for Ṁg> 5 × 10-7 M⊙ yr-1, regardless of the upper-level energy of the relevant transitions

  18. Mass-loss predictions for evolved very metal-poor massive stars

    NASA Astrophysics Data System (ADS)

    Muijres, L.; Vink, J. S.; de Koter, A.; Hirschi, R.; Langer, N.; Yoon, S.-C.

    2012-10-01

    Context. The first couple of stellar generations may have been massive, of order 100 M⊙, and to have played a dominant role in galaxy formation and the chemical enrichment of the early Universe. Some fraction of these objects may have died as pair-instability supernovae or gamma-ray bursts. The winds of these stars may have played an important role in determining these outcomes. As the winds are driven by radiation pressure on spectral lines, their strengths are expected to vary with metallicity. Until now, most mass-loss predictions for metal-poor O-type stars have assumed a scaled-down solar-abundance pattern. However, Population III evolutionary tracks show significant surface enrichment through rotational mixing of CNO-processed material, because even metal-poor stars switch to CNO-burning early on. Aims: We address the question of whether the CNO surface enhanced self-enrichment in the first few generations of stars could impact their mass-loss properties. Methods: We employ Monte Carlo simulations to establish the local line-force and solve for the momentum equation of the stellar outflow, testing whether an outflow can actually be established by assessing the net acceleration at the sonic point of the flow. Stellar evolution models of rotating metal-poor stars are used to specify the surface chemical composition, focussing on the phases of early enrichment. Results: We find that the mass-loss rates of CNO enhanced metal-poor stars are higher than those of non-enriched stars, but they are much lower than those rates where the CNO abundance is included in the total abundance Z. Metal-poor stars hotter than ~50 000 K, in the metallicity range investigated here (with an initial metallicity Z ≲ 10-4) are found to have no wind, as the high-ionization species of the CNO elements have too few strong lines to drive an outflow. We present a heuristic formula that provides mass-loss estimates for CNO-dominated winds in relation to scaled-down solar abundances

  19. Predictions for mass-loss rates and terminal wind velocities of massive O-type stars

    NASA Astrophysics Data System (ADS)

    Muijres, L. E.; Vink, Jorick S.; de Koter, A.; Müller, P. E.; Langer, N.

    2012-01-01

    Context. Mass loss from massive stars forms an important aspect of the evolution of massive stars, as well as for the enrichment of the surrounding interstellar medium. Aims: Our goal is to predict accurate mass-loss rates and terminal wind velocities. These quantities can be compared to empirical values, thereby testing radiation-driven wind models. One specific topical issue is that of the so-called "weak-wind problem", where empirically derived mass-loss rates and (modified) wind momenta fall orders of magnitude short of predicted values. Methods: We employ an established Monte Carlo model and a recently suggested new line acceleration formalism to solve the wind dynamics more consistently. Results: We provide a new grid of mass-loss rates and terminal wind velocities of O-type stars, and compare the values to empirical results. Our models fail to provide mass-loss rates for main-sequence stars below a luminosity of log(L/L⊙) = 5.2, where we appear to run into a fundamental limit. At luminosities below this critical value there is insufficient momentum transferred to the wind in the region below the sonic point in order to kick-start the acceleration of the flow. This problem occurs at almost the exact location of the onset of the weak-wind problem. For O dwarfs, the boundary between being able to start a wind, and failing to do so, is at spectral type O6/O6.5. The direct cause of this failure for O6.5 stars is a combination of the lower luminosity and a lack of Fe v lines at the base of the wind. This might indicate that - in addition to radiation pressure - another mechanism is required to provide the necessary driving to initiate the wind acceleration. Conclusions: For stars more luminous than 105.2 L⊙, our new mass-loss rates are in excellent agreement with the mass-loss prescription by Vink et al. (2000, A&A, 362, 295) using our terminal wind velocities as input to this recipe. This implies that the main assumption entering the method of the Vink et al

  20. Optically visible post-AGB stars, post-RGB stars and young stellar objects in the Large Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Kamath, D.; Wood, P. R.; Van Winckel, H.

    2015-12-01

    We have carried out a search for optically visible post-asymptotic giant branch (post-AGB) stars in the Large Magellanic Cloud (LMC). First, we selected candidates with a mid-IR excess and then obtained their optical spectra. We disentangled contaminants with unique spectra such as M stars, C stars, planetary nebulae, quasi-stellar objects and background galaxies. Subsequently, we performed a detailed spectroscopic analysis of the remaining candidates to estimate their stellar parameters such as effective temperature, surface gravity (log g), metallicity ([Fe/H]), reddening and their luminosities. This resulted in a sample of 35 likely post-AGB candidates with late-G to late-A spectral types, low log g, and [Fe/H] < -0.5. Furthermore, our study confirmed the existence of the dusty post-red giant branch (post-RGB) stars, discovered previously in our Small Magellanic Cloud survey, by revealing 119 such objects in the LMC. These objects have mid-IR excesses and stellar parameters (Teff, log g, [Fe/H]) similar to those of post-AGB stars except that their luminosities (< 2500 L⊙), and hence masses and radii, are lower. These post-RGB stars are likely to be products of binary interaction on the RGB. The post-AGB and post-RGB objects show spectral energy distribution properties similar to the Galactic post-AGB stars, where some have a surrounding circumstellar shell, while some others have a surrounding stable disc similar to the Galactic post-AGB binaries. This study also resulted in a new sample of 162 young stellar objects, identified based on a robust log g criterion. Other interesting outcomes include objects with an UV continuum and an emission line spectrum; luminous supergiants; hot main-sequence stars; and 15 B[e] star candidates, 12 of which are newly discovered in this study.

  1. Unexpectedly large mass loss during the thermal pulse cycle of the red giant star R Sculptoris.

    PubMed

    Maercker, M; Mohamed, S; Vlemmings, W H T; Ramstedt, S; Groenewegen, M A T; Humphreys, E; Kerschbaum, F; Lindqvist, M; Olofsson, H; Paladini, C; Wittkowski, M; de Gregorio-Monsalvo, I; Nyman, L-A

    2012-10-11

    The asymptotic-giant-branch star R Sculptoris is surrounded by a detached shell of dust and gas. The shell originates from a thermal pulse during which the star underwent a brief period of increased mass loss. It has hitherto been impossible to constrain observationally the timescales and mass-loss properties during and after a thermal pulse--parameters that determine the lifetime of the asymptotic giant branch and the amount of elements returned by the star. Here we report observations of CO emission from the circumstellar envelope and shell around R Sculptoris with an angular resolution of 1.3″. What was previously thought to be only a thin, spherical shell with a clumpy structure is revealed to also contain a spiral structure. Spiral structures associated with circumstellar envelopes have been previously seen, leading to the conclusion that the systems must be binaries. Combining the observational data with hydrodynamic simulations, we conclude that R Sculptoris is a binary system that underwent a thermal pulse about 1,800 years ago, lasting approximately 200 years. About 3 × 10(-3) solar masses of material were ejected at a velocity of 14.3 km s(-1) and at a rate around 30 times higher than the pre-pulse mass-loss rate. This shows that about three times more mass was returned to the interstellar medium during and immediately after the pulse than previously thought. PMID:23060194

  2. Greenland ice sheet surface temperature, melt and mass loss: 2000-06

    USGS Publications Warehouse

    Hall, D.K.; Williams, R.S., Jr.; Luthcke, S.B.; DiGirolamo, N.E.

    2008-01-01

    A daily time series of 'clear-sky' surface temperature has been compiled of the Greenland ice sheet (GIS) using 1 km resolution moderate-resolution imaging spectroradiometer (MODIS) land-surface temperature (LST) maps from 2000 to 2006. We also used mass-concentration data from the Gravity Recovery and Climate Experiment (GRACE) to study mass change in relationship to surface melt from 2003 to 2006. The mean LST of the GIS increased during the study period by ???0.27??Ca-1. The increase was especially notable in the northern half of the ice sheet during the winter months. Melt-season length and timing were also studied in each of the six major drainage basins. Rapid (<15 days) and sustained mass loss below 2000 m elevation was triggered in 2004 and 2005 as recorded by GRACE when surface melt begins. Initiation of large-scale surface melt was followed rapidly by mass loss. This indicates that surface meltwater is flowing rapidly to the base of the ice sheet, causing acceleration of outlet glaciers, thus highlighting the metastability of parts of the GIS and the vulnerability of the ice sheet to air-temperature increases. If air temperatures continue to rise over Greenland, increased surface melt will play a large role in ice-sheet mass loss.

  3. Analyzing Mass Loss and Tidal Circularization as a Source for Sustained Eccentric Orbits in Hot Jupiters

    NASA Astrophysics Data System (ADS)

    Salmon, Rachel L.; Sepinsky, Jeremy F.

    2015-01-01

    As the number of extrasolar planets and planet candidates increases, so does the number of systems that look strikingly different from our own. Hot Jupiters are such a system and are characterized by a Jupiter mass planet with a close-in orbit. Because of the proximity of the planet to its parent star, we would expect these systems to be tidally circularized. However, we observe many with significant eccentricities, suggesting that a mechanism must exist to account for sustained eccentric orbits. Previous analyses found that, in a population of eccentric hot Jupiters generated by planet-planet scattering, a significant fraction will overfill their Roche lobe at periastron. Other work has noted that mass loss in systems similar to hot Jupiters can act to increase the eccentricity of the orbit of a binary system. Here, we consider the effects of tidal circularization and mass loss on the orbital evolution of the hot Jupiters. By analyzing the balance between the tidal circularization and mass loss, we can determine an equilibrium eccentricity as a function of planet mass and the tidal quality factor, Q. If such an equilibrium value exists, then it is possible for this mechanism to be responsible for the sustained eccentric orbits of hot Jupiters that we observe. We present the orbital parameters for these equilibrium orbits over a broad parameter space and compare those results to the current population of observed extrasolar planets.

  4. DUST PRODUCTION AND MASS LOSS IN THE GALACTIC GLOBULAR CLUSTER 47 TUCANAE

    SciTech Connect

    McDonald, I.; Zijlstra, A. A.; Boyer, M. L.; Van Loon, J. Th.

    2011-04-01

    Dust production among post-main-sequence stars is investigated in the Galactic globular cluster 47 Tucanae (NGC 104) based on infrared photometry and spectroscopy. We identify metallic iron grains as the probable dominant opacity source in these winds. Typical evolutionary timescales of asymptotic giant branch stars suggest the mass-loss rates we report are too high. We suggest that this is because the iron grains are small or elongated and/or that iron condenses more efficiently than at solar metallicity. Comparison to other works suggests metallic iron is observed to be more prevalent toward lower metallicities. The reasons for this are explored, but remain unclear. Meanwhile, the luminosity at which dusty mass loss begins is largely invariant with metallicity, but its presence correlates strongly with long-period variability. This suggests that the winds of low-mass stars have a significant driver that is not radiation pressure, but may be acoustic driving by pulsations.

  5. Glaciers. Attribution of global glacier mass loss to anthropogenic and natural causes.

    PubMed

    Marzeion, Ben; Cogley, J Graham; Richter, Kristin; Parkes, David

    2014-08-22

    The ongoing global glacier retreat is affecting human societies by causing sea-level rise, changing seasonal water availability, and increasing geohazards. Melting glaciers are an icon of anthropogenic climate change. However, glacier response times are typically decades or longer, which implies that the present-day glacier retreat is a mixed response to past and current natural climate variability and current anthropogenic forcing. Here we show that only 25 ± 35% of the global glacier mass loss during the period from 1851 to 2010 is attributable to anthropogenic causes. Nevertheless, the anthropogenic signal is detectable with high confidence in glacier mass balance observations during 1991 to 2010, and the anthropogenic fraction of global glacier mass loss during that period has increased to 69 ± 24%. PMID:25123485

  6. Bone loss: Quantitative imaging techniques for assessing bone mass in rheumatoid arthritis

    PubMed Central

    Njeh, Christopher F; Genant, Harry K

    2000-01-01

    Osteoporosis is associated with low bone mass and microarchitectural deterioration of bone tissue with clinical manifestation of low trauma fractures. Rheumatoid arthritis (RA) is a risk factor due to generalized and articular bone loss. This minireview presents past and current bone mass measurement techniques in RA. These techniques include: plain radiographs, absorptiometry, quantitative computed tomography (QCT) and ultrasound. The most widely used technique is dual x-ray absorptiometry (DXA). RA patients have lower bone mass as compared with normals and substantial bone loss may occur early after the onset of disease. Measurement of bone mineral density (BMD) at the hand using either DXA or ultrasound maybe a useful tool in the management of RA patients. PMID:11094457

  7. Explaining individual variation in patterns of mass loss in breeding birds

    PubMed Central

    Rands, Sean A; Cuthill, Innes C; Houston, Alasdair I

    2006-01-01

    Background Studies of birds have a disproportionate representation in the literature on life-history evolution, because of the (apparent) ease with which the costs and benefits can be quantified and manipulated. During reproduction, birds frequently show a highly conserved pattern of mass change and changes in mass loss during breeding have been widely considered to be a valid short-term measure of the costs of reproduction. Experimental manipulations of the breeding attempts of birds usually argue that the presence of a response shows that a cost of reproduction exists, but there is little consensus as to how the size of these costs can be measured. Results We model this mass loss by considering how a parent can maximise its lifetime reproductive success, using a theoretical framework that is particularly suited to modelling parental care in altricial birds. If lifetime reproductive success is taken to be the sum of a parent's current and future reproductive success, we show that the exact forms of these components will influence the optimal amount of mass a parent should lose. In particular, we demonstrate that the shape of the relationship between parental investment and chick survival will lead to differing degrees of investment between parents of different initial qualities: parents with initially high levels of energy reserves could conceivably invested a lesser, similar or greater amount of resources than parents with initially low reserves, and these initially 'heavy' parents could potentially end up being lighter than the initially 'lighter' individuals. Conclusion We argue that it is difficult to make predictions about the dependence of a parent's final mass on its initial mass, and therefore mass loss should only be used as a short-term measure of the costs of reproduction with caution. The model demonstrates that we require a better understanding of the relationship between mass loss and both current and future reproductive success of the parent, before

  8. Contributions of Weight Perceptions to Weight Loss Attempts: Differences by Body Mass Index and Gender

    PubMed Central

    Lemon, Stephenie C.; Rosal, Milagros C.; Zapka, Jane; Borg, Amy; Andersen, Victoria

    2009-01-01

    Previous studies have consistently observed that women are more likely to perceive themselves as overweight compared to men. Similarly, women are more likely than men to report trying to lose weight. Less is known about the impact that self-perceived weight has on weight loss behaviors of adults and whether this association differs by gender. We conducted a cross-sectional analysis among an employee sample to determine the association of self-perceived weight on evidence-based weight loss behaviors across genders, accounting for body mass index (BMI) and demographic characteristics. Women were more likely than men to consider themselves to be overweight across each BMI category, and were more likely to report attempting to lose weight. However, perceiving oneself to be overweight was a strong correlate for weight loss attempts across both genders. The effect of targeting accuracy of self-perceived weight status in weight loss interventions deserves research attention. PMID:19188102

  9. A SEMI-EMPIRICAL MASS-LOSS RATE IN SHORT-PERIOD CATACLYSMIC VARIABLES

    SciTech Connect

    Sirotkin, Fedir V.; Kim, Woong-Tae E-mail: wkim@astro.snu.ac.k

    2010-10-01

    The mass-loss rate of donor stars in cataclysmic variables (CVs) is of paramount importance in the evolution of short-period CVs. Observed donors are oversized in comparison with those of isolated single stars of the same mass, which is thought to be a consequence of the mass loss. Using the empirical mass-radius relation of CVs and the homologous approximation for changes in effective temperature T{sub 2}, orbital period P, and luminosity of the donor with the stellar radius, we find the semi-empirical mass-loss rate M-dot{sub 2} of CVs as a function of P. The derived M-dot{sub 2} is at {approx}10{sup -9.5}-10{sup -10} M{sub sun} yr{sup -1} and weakly depends on P when P>90 minutes, while it declines very rapidly toward the minimum period when P < 90 minutes, emulating the P-T{sub 2} relation. Due to strong deviation from thermal equilibrium caused by the mass loss, the semi-empirical M-dot{sub 2} is significantly different from and has a less-pronounced turnaround behavior with P than suggested by previous numerical models. The semi-empirical P- M-dot{sub 2} relation is consistent with the angular momentum loss due to gravitational wave emission and strongly suggests that CV secondaries with 0.075 M{sub sun} < M{sub 2} < 0.2 M{sub sun} are less than 2 Gyr old. When applied to selected eclipsing CVs, our semi-empirical mass-loss rates are in good agreement with the accretion rates derived from the effective temperatures T{sub 1} of white dwarfs, suggesting that M-dot{sub 2} can be used to reliably infer T{sub 2} from T{sub 1}. Based on the semi-empirical M-dot{sub 2}, SDSS 1501 and 1433 systems that were previously identified as post-bounce CVs have yet to reach the minimal period.

  10. AGB nucleosynthesis at low metallicity: What can we learn from Carbon- and s-elements-enhanced metal-poor stars

    NASA Astrophysics Data System (ADS)

    Abate, C.; Pols, O. R.; Izzard, R. G.; Karakas, A. I.

    2013-02-01

    CEMP-s stars are very metal-poor stars with enhanced abundances of carbon and s-process elements. They form a significant proportion of the very metal-poor stars in the Galactic halo and are mostly observed in binary systems. This suggests that the observed chemical anomalies are due to mass accretion in the past from an asymptotic giant branch (AGB) star. Because CEMP-s stars have hardly evolved since their formation, the study of their observed abundances provides a way to probe our models of AGB nucleosynthesis at low metallicity. To this end we included in our binary evolution model the results of the latest models of AGB nucleosynthesis and we simulated a grid of 100 000 binary stars at metallicity Z = 0.0001 in a wide range of initial masses and separations. We compared our modelled stars with a sample of 60 CEMP-s stars from the SAGA database of metal-poor stars. For each observed CEMP-s star of the sample we found the modelled star that reproduces best the observed abundances. The result of this comparison is that we are able to reproduce simultaneously the observed abundance of the elements affected by AGB nucleosynthesis (e.g. C, Mg, s-elements) for about 60% of the stars in the sample.

  11. On the red giant branch mass loss in 47 Tucanae: Constraints from the horizontal branch morphology

    NASA Astrophysics Data System (ADS)

    Salaris, Maurizio; Cassisi, Santi; Pietrinferni, Adriano

    2016-05-01

    We obtain stringent constraints on the actual efficiency of mass loss for red giant branch stars in the Galactic globular cluster 47 Tuc, by comparing synthetic modelling based on stellar evolution tracks with the observed distribution of stars along the horizontal branch in the colour-magnitude-diagram. We confirm that the observed, wedge-shaped distribution of the horizontal branch can only be reproduced by accounting for a range of initial He abundances, in agreement with inferences from the analysis of the main sequence, and a red giant branch mass loss with a small dispersion. We carefully investigated several possible sources of uncertainty that could affect the results of the horizontal branch modelling, stemming from uncertainties in both stellar model computations and cluster properties, such as heavy element abundances, reddening, and age. We determine a firm lower limit of ~0.17M⊙ for the mass lost by red giant branch stars, corresponding to horizontal branch stellar masses between ~0.65M⊙ and ~0.73M⊙ (the range driven by the range of initial helium abundances). We also derive that in this cluster the amount of mass lost along the asymptotic giant branch stars is comparable to the mass lost during the previous red giant branch phase. These results confirm, for this cluster, the disagreement between colour-magnitude-diagram analyses and inferences from recent studies of the dynamics of the cluster stars, which predict a much less efficient red giant branch mass loss. A comparison between the results from these two techniques applied to other clusters is required to gain more insights about the origin of this disagreement.

  12. Mass loss from Luminous Blue Variables and Quasi-periodic Modulations of Radio Supernovae

    NASA Astrophysics Data System (ADS)

    Vink, J. S.; Kotak, R.

    2007-08-01

    Massive stars, supernovae (SNe), and long-duration gamma-ray bursts (GRBs) have a huge impact on their environment. Despite their importance, a comprehensive knowledge of which massive stars produce which SN/GRB is hitherto lacking. We present a brief overview about our knowledge of mass loss in the Hertzsprung-Russell Diagram (HRD) covering evolutionary phases of the OB main sequence, the unstable Luminous Blue Variable (LBV) stage, and the Wolf-Rayet (WR) phase. Despite the fact that metals produced by ``self-enrichment'' in WR atmospheres exceed the initial - host galaxy - metallicity, by orders of magnitude, a particularly strong dependence of the mass-loss rate on the initial metallicity is found for WR stars at sub-solar metallicities (1/10 - 1/100 solar). This provides a significant boost to the collapsar model for GRBs, as it may present a viable mechanism to prevent the loss of angular momentum by stellar winds at low metallicity, whilst strong Galactic WR winds may inhibit GRBs occurring at solar metallicities. Furthermore, we discuss recently reported quasi-sinusoidal modulations in the radio lightcurves of SNe 2001ig and 2003bg. We show that both the sinusoidal behaviour and the recurrence timescale of these modulations are consistent with the predicted mass-loss behaviour of LBVs, and we suggest LBVs may be the progenitors of some core-collapse SNe.

  13. SAO 244567 - A post-AGB star which has turned into a planetary nebula within the last 40 years

    NASA Astrophysics Data System (ADS)

    Parthasarathy, M.; Garcia-Lario, P.; Pottasch, S. R.; Manchado, A.; Clavel, J.; de Martino, D.; van de Steene, G. C. M.; Sahu, K. C.

    1993-01-01

    SAO 244567 (Hen 1357 = CPD -59 deg 6926 = IRAS 17119-5926) is an IRAS source with far infrared colors and flux distribution similar to those of planetary nebulae. The IUE ultraviolet spectra obtained in July 1988 and April 1992 show nebular emission lines, and also the changes in the spectra suggest the formation of the planetary nebula and the rapid evolution of the central star. The optical spectrum of this star obtained by Henize around 1950 shows only the H-alpha line in emission, while the most recent one, obtained in 1990 shows strong forbidden emission lines corresponding to a low excitation and young planetary nebula. The IUE ultraviolet spectra show evidence for the presence of stellar wind and mass loss. The stellar lines show P-Cygni type profiles and the terminal velocity of the stellar wind is about - 3000 km/s. The spectral type of the central star is O8 V. The presence of a detached cold dust shell (125 K), high galactic latitude and abundances suggest that SAO 244567 has recently evolved from a low or intermediate mass progenitor star which has ejected its outer envelope during the AGB stage of evolution and is rapidly evolving towards hotter spectral types.

  14. Photogrammetrically Derived Estimates of Glacier Mass Loss in the Upper Susitna Drainage Basin, Alaska Range, Alaska

    NASA Astrophysics Data System (ADS)

    Wolken, G. J.; Whorton, E.; Murphy, N.

    2014-12-01

    Glaciers in Alaska are currently experiencing some of the highest rates of mass loss on Earth, with mass wastage rates accelerating during the last several decades. Glaciers, and other components of the hydrologic cycle, are expected to continue to change in response to anticipated future atmospheric warming, thus, affecting the quantity and timing of river runoff. This study uses sequential digital elevation model (DEM) analysis to estimate the mass loss of glaciers in the upper Susitna drainage basin, Alaska Range, for the purpose of validating model simulations of past runoff changes. We use mainly stereo optical airborne and satellite data for several epochs between 1949 and 2014, and employ traditional stereo-photogrammetric and structure from motion processing techniques to derive DEMs of the upper Susitna basin glaciers. This work aims to improve the record of glacier change in the central Alaska Range, and serves as a critical validation dataset for a hydrological model that simulates the potential effects of future glacier mass loss on changes in river runoff over the lifespan of the proposed Susitna-Watana Hydroelectric Project.

  15. The first mass and angular momentum loss measurements for a CV-like binary

    NASA Astrophysics Data System (ADS)

    Drake, Jeremy

    2014-10-01

    The period distribution of close binaries, cataclysmic variables, novae and single-degenerate SN1a progenitor candidates is largely controlled by magnetically-driven mass and angular momentum loss (AML) from the M dwarf secondary. The mass loss rates for these spun-up stars remain essentially unknown and impossible to observe directly, with likely values in the range 1e-12 to 1e-15 Msun/yr. AML presciptions for CVs differ by orders of magnitude. One way to measure the mass loss rate is to observe the dM wind accrete onto its WD companion in a pre-CV very close to Roche Lobe overflow but lacking the obscuring complications and emission from an accretion disk. The measurement can be combined with realistic MHD models to understand the accretion fraction, the mass that escapes, and the AML. The best-studied nearby pre-CV is QS Vir (48pc, P=3.6hr). However, its wind accretion rates measured from 1999 HST UV spectra of the WD metal absorption lines and 2006 XMM-Newton CCD spectroscopy differ by a factor of a thousand, pointing to either a dominant CME stochastic component, or a "magnetic switch" found in MHD simulations and driven by cyclic activity on the M dwarf. HST COS spectra combined with XMM-Newton monitoring on timescales from weeks to years will tease out CME vs cyclic accretion variations. UV and X-ray measurements will provide the first consistency check of both accretion rate measurement methods. MHD models tailored to the system will enable the first quasi-direct measurements of the mass loss and AML from a CV-like binary. Our project requires 6 HST/COS orbits in Cycles 22-24, and 60ksec on XMM in Cycle 22

  16. Sharply increased mass loss from glaciers and ice caps in the Canadian Arctic Archipelago.

    PubMed

    Gardner, Alex S; Moholdt, Geir; Wouters, Bert; Wolken, Gabriel J; Burgess, David O; Sharp, Martin J; Cogley, J Graham; Braun, Carsten; Labine, Claude

    2011-05-19

    Mountain glaciers and ice caps are contributing significantly to present rates of sea level rise and will continue to do so over the next century and beyond. The Canadian Arctic Archipelago, located off the northwestern shore of Greenland, contains one-third of the global volume of land ice outside the ice sheets, but its contribution to sea-level change remains largely unknown. Here we show that the Canadian Arctic Archipelago has recently lost 61 ± 7 gigatonnes per year (Gt yr(-1)) of ice, contributing 0.17 ± 0.02 mm yr(-1) to sea-level rise. Our estimates are of regional mass changes for the ice caps and glaciers of the Canadian Arctic Archipelago referring to the years 2004 to 2009 and are based on three independent approaches: surface mass-budget modelling plus an estimate of ice discharge (SMB+D), repeat satellite laser altimetry (ICESat) and repeat satellite gravimetry (GRACE). All three approaches show consistent and large mass-loss estimates. Between the periods 2004-2006 and 2007-2009, the rate of mass loss sharply increased from 31 ± 8 Gt yr(-1) to 92 ± 12 Gt yr(-1) in direct response to warmer summer temperatures, to which rates of ice loss are highly sensitive (64 ± 14 Gt yr(-1) per 1 K increase). The duration of the study is too short to establish a long-term trend, but for 2007-2009, the increase in the rate of mass loss makes the Canadian Arctic Archipelago the single largest contributor to eustatic sea-level rise outside Greenland and Antarctica. PMID:21508960

  17. Rb and Zr abundances in massive Galactic AGB stars revisited

    NASA Astrophysics Data System (ADS)

    Pérez-Mesa, V.; Zamora, O.; García-Hernández, D. A.; Plez, B.; Manchado, A.; Karakas, A. I.; Lugaro, M.

    2016-07-01

    We report new abundances of Rb and Zr in a sample of massive Galactic asymptotic giant branch (AGB) stars that were previously studied with hydrostatic models by using more realistic dynamical model atmospheres. We use a modified version of the spectral synthesis code Turbospectrum, and consider the presence of a circumstellar envelope and a radial wind in the modelling of these Galactic AGB stars. The Rb and Zr are determined from the 7800 Å Rb I resonant line and the 6474 Å ZrO bandhead, respectively, and they are compared with the AGB nucleosynthesis theoretical predictions. The derived Rb abundances are much lower (∼⃒1-2 dex) with the new dynamical models, while the Zr abundances, however, are closer to the hydrostatic values. The new model atmospheres can help to resolve the problem of the mismatch between the observations and the nucleosynthesis theoretical predictions of massive AGB stars.

  18. EUV-driven mass loss of protoplanetary cores with hydrogen-dominated atmospheres: The influences of ionization and orbital distance

    NASA Astrophysics Data System (ADS)

    Erkaev, N. V.; Lammer, H.; Odert, P.; Kislyakova, K. G.; Johnstone, C. P.; Güdel, M.; Khodachenko, M. L.

    2016-04-01

    We investigate the loss rates of the hydrogen atmospheres of terrestrial planets with a range of masses and orbital distances by assuming a stellar extreme ultraviolet (EUV) luminosity that is 100 times stronger than that of the current Sun. We apply a 1D upper atmosphere radiation absorption and hydrodynamic escape model that takes into account ionization, dissociation and recombination to calculate hydrogen mass loss rates. We study the effects of the ionization, dissociation and recombination on the thermal mass loss rates of hydrogen-dominated super-Earths and compare the results to those obtained by the energy-limited escape formula which is widely used for mass loss evolution studies. Our results indicate that the energy-limited formula can to a great extent over- or underestimate the hydrogen mass loss rates by amounts that depend on the stellar EUV flux and planetary parameters such as mass, size, effective temperature, and EUV absorption radius.

  19. Greenland Ice Sheet Mass Balance: Distribution of Increased Mass Loss with Climate Warming; 2003-07 Versus 1992-2002

    NASA Technical Reports Server (NTRS)

    Zwally, H. Jay; Li, Jun; Benner, Anita C.; Beckley, Matthew; Cornejo, Helen G.; DiMarzio, John; Giovinetto, Mario B.; Neumann, Thomas A.; Robbins, John; Saba, Jack L.; Yi, Donghui; Wang, Weili

    2011-01-01

    We derive mass changes of the Greenland ice sheet (GIS) for 2003-07 from ICESat laser altimetry and compare them with results for 1992-2002 from ERS radar and airborne laser altimetry. The GIS continued to grow inland and thin at the margins during 2003 07, but surface melting and accelerated flow significantly increased the marginal thinning compared with the 1990s. The net balance changed from a small loss of 7 plus or minus 3 Gt a 1(sup -1) in the 1990s to 171 plus or minus 4 Gt a (sup -1) for 2003-07, contributing 0.5 mm a(sup -1) to recent global sea-level rise. We divide the derived mass changes into two components: (1) from changes in melting and ice dynamics and (2) from changes in precipitation and accumulation rate. We use our firn compaction model to calculate the elevation changes driven by changes in both temperature and accumulation rate and to calculate the appropriate density to convert the accumulation-driven changes to mass changes. Increased losses from melting and ice dynamics (17-206 Gt a(sup-1) are over seven times larger than increased gains from precipitation (10 35 Gt a(sup-1) during a warming period of approximately 2 K (10 a)(sup -1) over the GIS. Above 2000m elevation, the rate of gain decreased from 44 to 28 Gt a(sup-1), while below 2000m the rate of loss increased from 51 to 198 Gt a(sup-1). Enhanced thinning below the equilibrium line on outlet glaciers indicates that increased melting has a significant impact on outlet glaciers, as well as accelerating ice flow. Increased thinning at higher elevations appears to be induced by dynamic coupling to thinning at the margins on decadal timescales.

  20. Water Mass Loss of the Himalayas from GRACE, ICESat and SRTM

    NASA Astrophysics Data System (ADS)

    Muskett, Reginald

    2010-05-01

    The Himalayas and the Tibet Plateau form a region of about 3.4 million square kilometers. Home to numerous large lakes and tarns (glacier lakes), and to more than 50,000 glaciers and high-elevation snowfields, this region is the source of the Indus, Ganga, Brahmaputra, and Yamuna Rivers, the Indo-Gangetic River system. The Himalayan Mountains and associated ranges form a boundary separating continental air masses associated with the westerlies, and marine air masses associated with the summer South Asian monsoon. Adverse changes in water storage / river discharge driven by effects of climate change will impact agriculture, hydroelectric power facilities, commerce, and the lives of more than 1.3 billion people. We are investigating water mass loss derived by the Gravity Recovery and Climate Experiment (GRACE), the ICE, Cloud and land Elevation (ICESat) and the Shuttle Radar Topograghy Mission (SRTM). In our current analysis we remove the effects of isostatic glacial adjustment and both retain and remove the annual cycle of water equivalent mass change for evaluation. Least-squares regression of GRACE monthly time-series shows the Himalaya region lost 17.9 ± 11.0 km3/yr water equivalent mass from August 2002 through December 2006 (annual cycle removed basis). Retaining the annual cycle of water equivalent mass change and extending the time series for one additional year, the least-squares trend is 9.9 ± 4.7 km3/yr of water equivalent mass loss from August 2002 through December 2007. Comparison of same-datum ICESat and SRTM elevations above 5000 meters shows snow surface elevations are decreasing at 1.1 ± 0.7 m/yr from June 2005 through April 2007. We will present updated analyses of the trends of regional water equivalent mass and elevation changes from GRACE and ICESat - SRTM measurements.

  1. Spectroscopic survey of post-AGB star candidates

    NASA Astrophysics Data System (ADS)

    Pereira, C. B.; Miranda, L. F.

    2007-01-01

    Aims:Our goal is to establish the true nature of post-AGB star candidates and to identify new post-AGB stars. Methods: We used low resolution optical spectroscopy and we compared the spectra of the candidate post-AGB stars with those of stars in the library specta available in the literature and with spectra of "standard" post-AGB stars, and direct imaging in narrow-band filters. Results: Spectra were obtained for 16 objects: 14 objects have not been observed previously and 2 objects are already known post-AGB stars used as "standards" for identification. From the spectra we identify: six new post-AGB stars with spectral types between G5 and F5, two H ii regions the morphology of which is revealed in the direct images for the first time, a G giant with infrared emission, a young stellar object, a probable post-AGB star with emission lines and three objects for which the classification is still unclear. As a whole, our results provide new, reliable identifications for 10 objects among listed post-AGB star candidates. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC), and at the Observatorio de Sierra Nevada, which is operated by the Consejo Superior de Investigaciones Científicas through the Instituto de Astrofísica de Andalucía (Granada, Spain). Appendices A-D are only available in electronic form at http://www.aanda.org

  2. Linking the spatial variability of glacier mass loss to fjord geometry

    NASA Astrophysics Data System (ADS)

    Porter, D. F.; Tinto, K. J.; Boghosian, A.; Cochran, J. R.; Csatho, B. M.; Bell, R. E.

    2015-12-01

    There is compelling evidence of increasing mass loss of the ice sheets using a diverse set of observations, including increased thinning rates measured from both airborne and satellite altimeters, elevated mass fluxes resulting from the acceleration of outlet glaciers, and mass changes measured directly from satellite gravimetry. A dominant characteristic of observed change in Greenland outlet glaciers is that it is locally random. Numerous studies have revealed a high degree of spatial and temporal variability of outlet glacier mass change. Modeling studies suggest that increased ocean temperatures may be responsible for the observed glacial retreat in Greenland through increased basal melting, leading to increased calving rates, terminus retreat, glacier speedup, and eventually thinning of inland ice. Knowledge of fjord geometry is crucial for ice-ocean interaction because the availability of ocean heat to the ice will be restricted by narrow sills and shallow grounding lines. We investigate whether the variability in observed changes among Greenland glaciers can be partially explained by variation in fjord geometry. Using statistical techniques commonly employed to detect patterns in complex spatial data, we objectively show that mass change in Greenland tidewater glaciers between 2003 and 2009 is indeed mostly spatially incoherent. Except for a few clusters of similar change in the NW and Scoresby Sund regions, there is significant glacier-scale variability in mass loss rates. To understand the drivers of this local variability, we compare fjord bathymetries from all regions of Greenland, modeled using airborne gravimetry measurements from NASA Operation IceBridge flights, to estimates of glaciological change. Specifically, we investigate the correlation between water depths at the grounding line and the dynamic mass loss of tidewater glaciers. In theory, a deep grounding line will allow greater interaction with the warm Atlantic Water observed in most fjords

  3. AGB Stars in the Large and Small Magellanic Clouds

    NASA Astrophysics Data System (ADS)

    Portman, Matthew; Sargent, Benjamin A.; Held, Leander; Kastner, Joel; SAGE Team

    2016-01-01

    Asymptotic giant branch (AGB) stars are evolved, pulsating variable stars that generate massive outflows of gas and dust, thereby enriching the interstellar medium (ISM) in the products of stellar nucleosynthesis. Recent studies find the dustiest, most extreme AGB stars contribute a disproportionately large amount of matter to their host galaxies; these extreme AGB stars are also the most variable, and they emit most of their energy at mid-infrared wavelengths. Therefore, using the Spitzer Space Telescope, we have imaged several target AGB stars identified in previous surveys of the Large and Small Magellanic Clouds (LMC and SMC, respectively). Our aim is to obtain light curves at 3.6 and 4.5 microns wavelength for these extreme AGB stars. Using multiple epochs of data taken within the last 3 years by our survey and then further comparing this data to past surveys of the SMC and LMC with Spitzer, we were able to generate preliminary light curves for a sample of 30 extreme AGB stars, as well as for other stars found within the image fields. This research project was made possible by the Rochester Institute of Technology Center for Imaging Science Research Experience for Undergraduates program, funded by National Science Foundation grant PHY-1359361 to RIT.

  4. Use of plume mapping data to estimate chlorinated solvent mass loss

    USGS Publications Warehouse

    Barbaro, J.R.; Neupane, P.P.

    2006-01-01

    Results from a plume mapping study from November 2000 through February 2001 in the sand-and-gravel surficial aquifer at Dover Air Force Base, Delaware, were used to assess the occurrence and extent of chlorinated solvent mass loss by calculating mass fluxes across two transverse cross sections and by observing changes in concentration ratios and mole fractions along a longitudinal cross section through the core of the plume. The plume mapping investigation was conducted to determine the spatial distribution of chlorinated solvents migrating from former waste disposal sites. Vertical contaminant concentration profiles were obtained with a direct-push drill rig and multilevel piezometers. These samples were supplemented with additional ground water samples collected with a minipiezometer from the bed of a perennial stream downgradient of the source areas. Results from the field program show that the plume, consisting mainly of tetrachloroethylene (PCE), trichloroethene (TCE), and cis-1,2-dichloroethene (cis-1,2-DCE), was approximately 670 m in length and 120 m in width, extended across much of the 9- to 18-m thickness of the surficial aquifer, and discharged to the stream in some areas. The analyses of the plume mapping data show that losses of the parent compounds, PCE and TCE, were negligible downgradient of the source. In contrast, losses of cis-1,2-DCE, a daughter compound, were observed in this plume. These losses very likely resulted from biodegradation, but the specific reaction mechanism could not be identified. This study demonstrates that plume mapping data can be used to estimate the occurrence and extent of chlorinated solvent mass loss from biodegradation and assess the effectiveness of natural attenuation as a remedial measure.

  5. Early solar mass loss, opacity uncertainties, and the solar abundance problem

    SciTech Connect

    Guzik, Joyce Ann; Keady, John; Kilcrease, David

    2009-01-01

    Solar models calibrated with the new element abundance mixture of Asplund et al. published in 2005 no longer produce good agreement with the sound speed, convection zone depth, and convection zone helium abundance inferred from solar oscillation data. Attempts to modify the input physics of the standard model, for example, by including enhanced diffusion, increased opacities, accretion, convective overshoot, or gravity waves have not restored the good agreement attained with the prior abundances. Here we present new models including early mass loss via a stronger solar wind. Early mass loss has been investigated prior to the solar abundance problem to deplete lithium and resolve the 'faint early sun problem'. We find that mass loss modifies the core structure and deepens the convection zone, and so improves agreement with oscillation data using the new abundances: however the amount of mass loss must be small to avoid destroying all of the surface lithium, and agreement is not fully restored. We also considered the prospects for increasing solar interior opacities. In order to increase mixture opacities by the 30% required to mitigate the abundance problem, the opacities of individual elements (e.g., O, N, C, and Fe) must be revised by a factor of two to three for solar interior conditions: we are investigating the possibility of broader calculated line wings for bound-bound transitions at the relevant temperatures to enhance opacity. We find that including all of the elements in the AGS05 opacity mixture (through uranium at atomic number Z=92) instead of only the 17 elements in the OPAL opacity mixture increases opacities by a negligible 0.2%.

  6. Mass loss rates from protostars and OI(63 micron) shock luminosities

    NASA Technical Reports Server (NTRS)

    Hollenbach, D.

    1985-01-01

    The high-velocity ejection of material from protostars results in a wind shock which may be observable in OI(63 micron) emission. It is shown that for a wide range of conditions, the OI(63 micron) luminosity is proportional to the mass loss rate from the protostar. Application is made to shock OI(63 micron) emission observed around IRc2 in the BN-KL region of Orion.

  7. Model atmospheres with periodic shocks. [pulsations and mass loss in variable stars

    NASA Technical Reports Server (NTRS)

    Bowen, G. H.

    1989-01-01

    The pulsation of a long-period variable star generates shock waves which dramatically affect the structure of the star's atmosphere and produce conditions that lead to rapid mass loss. Numerical modeling of atmospheres with periodic shocks is being pursued to study the processes involved and the evolutionary consequences for the stars. It is characteristic of these complex dynamical systems that most effects result from the interaction of various time-dependent processes.

  8. The role of dust in mass loss from late-type stars

    NASA Technical Reports Server (NTRS)

    Jura, M.

    1986-01-01

    It is noted that, in almost all late-type stars with measured mass loss rates, there is sufficient momentum in the radiation to dominate the dynamics. The opacity of the material is sufficiently great to render radiation pressure important; the dust forms close enough to the central star for radiation pressure to account for the observed outflow velocities. Pulsations appear to be important in raising the material far enough above the photosphere for grains to condense.

  9. Yohkoh/SXT soft x-ray observations of sudden mass loss from the solar corona

    NASA Technical Reports Server (NTRS)

    Hudson, H. S.; Acton, L. W.; Alexander, D.; Freeland, S. L.; Lemen, J. R.; Harvey, K. L.

    1995-01-01

    Direct X-ray observations allow us to estimate the hot coronal mass before and after a flare or other disturbance of the type leading to a coronal mass ejection. The sudden disappearance of a large coronal structure (scale greater than 105 km) gives evidence that an ejection has occurred, if the time scales are much shorter than the conductive or radiative cooling times for such structures. A flare also typically adds large amounts of new material to the corona via evaporation resulting from the coronal energy release. This provides a competing mechanism that makes the estimation of the total mass loss somewhat difficult. We note that the X-ray observations have the advantage of covering the entire corona rather than the limb regions unlike the coronagraph observations. We have identified two examples of coronal mass disappearances. before and during long duration flare events on 21 Feb. 1992 (on the E limb) and 13 Nov. 1994 (near disk center). In latter case the total mass amounted to some 4 x 10(exp 14) g with a density of 3 x 10(exp 8)cm(exp -3) and a temperature of 2.8 MK before its disappearance. This corresponds to a radiative cooling time of some 104 S. much longer than the observed time of disappearance. We therefore suggest that these sudden mass disappearances correspond with coronal mass ejections (CMEs), and suggest that further data analysis will be able to confirm this by comparison with optical observations of specific CMEs.

  10. Losses of Energetic Electrons in Earth's Outer Radiation Belt During Unusual Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Lugaz, Noé; Huang, Chia-Lin; Schwadron, Nathan; Spence, Harlan; Farrugia, Charles; Winslow, Reka

    2016-07-01

    The most extreme changes in solar wind parameters important for the coupling between the solar wind and the magnetosphere (dynamic pressure, dawn-to-dusk electric field, Alfven Mach number, plasma beta, …) occur during the passage at Earth of coronal mass ejections (CMEs). While the response of Earth's radiation belts to CMEs and CME-driven shocks has been investigated in great details, few studies have focused on what makes some CMEs and their shocks especially effective in driving losses of energetic electrons in the outer radiation belt. Here, we present specific examples of losses during the passage at Earth of a coronal mass ejection. In particular, we discuss the conditions which may result in the magnetopause to retreat earthward up to geosynchronous orbit, resulting in significant losses of energetic electrons due to magnetopause shadowing. We also present the result of a low-density magnetic ejecta which impacted Earth in January 2013. Combining interplanetary, magnetosheath, outer magnetosphere and radiation belt measurements by more than ten satellites, including the Van Allen Probes, THEMIS and Cluster, we show how a period of extremely low Mach number and dynamic pressure during the passage of the magnetic cloud resulted in dramatic losses in the outer radiation belt and a large-scale reorganization of the entire day-side magnetosphere.

  11. Empirical mass-loss rates for 25 O and early B stars, derived from Copernicus observations

    NASA Technical Reports Server (NTRS)

    Gathier, R.; Lamers, H. J. G. L. M.; Snow, T. P.

    1981-01-01

    Ultraviolet line profiles are fitted with theoretical line profiles in the cases of 25 stars covering a spectral type range from O4 to B1, including all luminosity classes. Ion column densities are compared for the determination of wind ionization, and it is found that the O VI/N V ratio is dependent on the mean density of the wind and not on effective temperature value, while the Si IV/N V ratio is temperature-dependent. The column densities are used to derive a mass-loss rate parameter that is empirically correlated against the mass-loss rate by means of standard stars with well-determined rates from IR or radio data. The empirical mass-loss rates obtained are compared with those derived by others and found to vary by as much as a factor of 10, which is shown to be due to uncertainties or errors in the ionization fractions of models used for wind ionization balance prediction.

  12. Mass Loss Rates for Solar-like Stars Measured from Lyα Absorption

    NASA Astrophysics Data System (ADS)

    Wood, B. E.; Müller, H.-R.; Linsky, J. L.

    2003-10-01

    We present a number of mass loss rate measurements for solar-like stars with coronal winds, computed using a Lyα absorption technique. The collision between the solar wind and the interstellar wind seen by the Sun defines the large scale structure of our heliosphere. Similar structures, ``astrospheres,'' exist around other solar-like stars. The deceleration of the interstellar wind at the solar or stellar bow shock heats the interstellar material. Heated neutral hydrogen in the outer astrosphere (and/or heliosphere) produces a broad Lyα absorption profile that is often detectable in high resolution Hubble Space Telescope spectra. The amount of absorption is dependent upon the strength of the stellar wind. With guidance from hydrodynamic models of astrospheres, we use detected astrospheric Lyα absorption to estimate the stellar mass loss rates. For the solar-like GK stars in our sample, mass loss appears to increase with stellar activity, suggesting that young, active stars have stronger winds than old, inactive stars. However, Proxima Cen (M5.5 Ve) and λ And (G8 IV-III+M V) appear to be inconsistent with this relation.

  13. Assessing the mass loss of glaciers using ICESat laser altimetry data

    NASA Astrophysics Data System (ADS)

    Bolch, Tobias

    2014-05-01

    The melt water of the glaciers on earth makes a substantial contribution to global sea-level rise. However, until recently most estimates relied on the extrapolation of measurements of few glaciers only which were upscaled to larger regions. Space-borne laser altimetry data from the ICESat GLAS sensor provides a global data set of elevation changes for the period 2003 - 2009. The accuracy of the altimetry measurements of about ±0.5 m even over rough surfaces along with their small footprint (about 70 m) is making this data very suitable to assess elevation changes not only for the two ice sheets but also for the glaciers. This data set in combination with the recently finalized global glacier inventory (Randolph Glacier Inventory) allowed the first time to determine the glacier volume changes for larger regions. A major challenge with ICESat data is the sparse density of the tracks with increasing horizontal separation with decreasing latitude (from about 10 km up to more than 50 km), and the fact that the repeat tracks can be several hundred metres apart. Plane fitting and the comparison to the available global DEMs (SRTM and GDEM) is required to correct for the repeat track separation. The obtained elevation changes are usually extrapolated to larger glazierized regions based on the glacier hypsometries. Results of two different studies of the local glaciers and ice caps on Greenland using similar data match well for the volume change (-40 km³ vs. -42 km³) with the highest loss in the south-eastern sector and lowest in the northern sector of Greenland. However, they vary between 28 ± 11 and 38 ± 7 Gt a-1 (~10 - 15% mass loss of glaciers on earth) due to different ice-density assumptions. Hence, while the measurements seem to be accurate the major challenge for assessing the glacier mass changes (and hence, their contribution to sea is the conversion from elevation changes to mass changes as snow and ice density and firn compaction have to be estimated or

  14. Accelerated modern human–induced species losses: Entering the sixth mass extinction

    PubMed Central

    Ceballos, Gerardo; Ehrlich, Paul R.; Barnosky, Anthony D.; García, Andrés; Pringle, Robert M.; Palmer, Todd M.

    2015-01-01

    The oft-repeated claim that Earth’s biota is entering a sixth “mass extinction” depends on clearly demonstrating that current extinction rates are far above the “background” rates prevailing between the five previous mass extinctions. Earlier estimates of extinction rates have been criticized for using assumptions that might overestimate the severity of the extinction crisis. We assess, using extremely conservative assumptions, whether human activities are causing a mass extinction. First, we use a recent estimate of a background rate of 2 mammal extinctions per 10,000 species per 100 years (that is, 2 E/MSY), which is twice as high as widely used previous estimates. We then compare this rate with the current rate of mammal and vertebrate extinctions. The latter is conservatively low because listing a species as extinct requires meeting stringent criteria. Even under our assumptions, which would tend to minimize evidence of an incipient mass extinction, the average rate of vertebrate species loss over the last century is up to 100 times higher than the background rate. Under the 2 E/MSY background rate, the number of species that have gone extinct in the last century would have taken, depending on the vertebrate taxon, between 800 and 10,000 years to disappear. These estimates reveal an exceptionally rapid loss of biodiversity over the last few centuries, indicating that a sixth mass extinction is already under way. Averting a dramatic decay of biodiversity and the subsequent loss of ecosystem services is still possible through intensified conservation efforts, but that window of opportunity is rapidly closing. PMID:26601195

  15. Ambient hypoxia enhances the loss of muscle mass after extensive injury

    PubMed Central

    Koulmann, N.; Meunier, A.; Pugnière, P.; McCarthy, J. J.; Beaudry, M.; Bigard, X.

    2016-01-01

    Hypoxia induces a loss of skeletal muscle mass and alters myogenesis in vitro, but whether it affects muscle regeneration in vivo following injury remains to be elucidated. We hypothesized that hypoxia would impair the recovery of muscle mass during regeneration. To test this hypothesis, the soleus muscle of female rats was injured by notexin and allowed to recover for 3, 7, 14, and 28 days under normoxia or hypobaric hypoxia (5,500 m) conditions. Hypoxia impaired the formation and growth of new myofibers and enhanced the loss of muscle mass during the first 7 days of regeneration, but did not affect the final recovery of muscle mass at 28 days. The impaired regeneration under hypoxic conditions was associated with a blunted activation of mechanical target of rapamycin (mTOR) signaling as assessed by p70S6K and 4E-BP1 phosphorylation that was independent of Akt activation. The decrease in mTOR activity with hypoxia was consistent with the increase in AMP-activated protein kinase activity, but not related to the change in regulated in development and DNA response 1 protein content. Hypoxia increased the mRNA levels of the atrogene muscle ring finger-1 after 7 days of regeneration, though muscle atrophy F box transcript levels remained unchanged. The increase in MyoD and myogenin mRNA expression with regeneration was attenuated at 7 days with hypoxia. In conclusion, our results support the notion that the enhanced loss of muscle mass observed after 1 week of regeneration under hypoxic conditions could mainly result from the impaired formation and growth of new fibers resulting from a reduction in protein synthesis and satellite cell activity. PMID:23974966

  16. Interplay between pulsations and mass loss in the blue supergiant 55 Cygnus = HD 198 478

    NASA Astrophysics Data System (ADS)

    Kraus, M.; Haucke, M.; Cidale, L. S.; Venero, R. O. J.; Nickeler, D. H.; Németh, P.; Niemczura, E.; Tomić, S.; Aret, A.; Kubát, J.; Kubátová, B.; Oksala, M. E.; Curé, M.; Kamiński, K.; Dimitrov, W.; Fagas, M.; Polińska, M.

    2015-09-01

    Context. Blue supergiant stars are known to display photometric and spectroscopic variability that is suggested to be linked to stellar pulsations. Pulsational activity in massive stars strongly depends on the star's evolutionary stage and is assumed to be connected with mass-loss episodes, the appearance of macroturbulent line broadening, and the formation of clumps in the wind. Aims: To investigate a possible interplay between pulsations and mass-loss, we carried out an observational campaign of the supergiant 55 Cyg over a period of five years to search for photospheric activity and cyclic mass-loss variability in the stellar wind. Methods: We modeled the H, He i, Si ii, and Si iii lines using the nonlocal thermal equilibrium atmosphere code FASTWIND and derived the photospheric and wind parameters. In addition, we searched for variability in the intensity and radial velocity of photospheric lines and performed a moment analysis of the line profiles to derive frequencies and amplitudes of the variations. Results: The Hα line varies with time in both intensity and shape, displaying various types of profiles: P Cygni, pure emission, almost complete absence, and double or multiple peaked. The star undergoes episodes of variable mass-loss rates that change by a factor of 1.7-2 on different timescales. We also observe changes in the ionization rate of Si ii and determine a multiperiodic oscillation in the He i absorption lines, with periods ranging from a few hours to 22.5 days. Conclusions: We interpret the photospheric line variations in terms of oscillations in p-, g-, and strange modes. We suggest that these pulsations can lead to phases of enhanced mass loss. Furthermore, they can mislead the determination of the stellar rotation. We classify the star as a post-red supergiant, belonging to the group of α Cyg variables. Based on observations taken with the Perek 2m telescope at Ondřejov Observatory, Czech Republic, and the Poznan Spectroscopic Telescope 2 at

  17. Analysis of Mass Loss of a Polymeric Composite under Space Radiations

    NASA Astrophysics Data System (ADS)

    Khasanshin, Rashid

    2016-07-01

    Polymeric materials find ever-widening application in space technique. This is tied with the simplicity of producing the polymeric-based composites with the predetermined set of properties. However, these materials in space become the sources of volatile products that increase density of spacecraft outer atmosphere that undermines on serviceability of the on-board equipment. Therefore, study of mass loss of spacecraft materials in service conditions is a vital task. Polymeric composites are often used as thermal control coatings (TCC), which are subjected to maximum radiation exposure in service. It is known that irradiation of a PC is accompanied by intense gas formation but evolution of volatile products (VP) through the material-vacuum surface is limited by diffusion. Well-developed surface together with little thickness of a TCC film facilitate migration of radiolysis products to free coating surface. In this case outgassing and destruction of material augment permeability of the film, accelerate migration processes and make them easier. This work is devoted to studying action of separate (electron, proton, and electromagnetic), paired, and the whole set of radiations on mass loss of a pattern material in vacuum. The primary focus was on studying and interpretation of synergistic effects appearing in the course of mass loss of the pattern materials EKOM-1 and EKOM-2 polymeric composites, the widely used spacecraft TCC. Irradiation was made by 20-50-keV electrons and 20-keV protons and electromagnetic radiation in vacuum chamber of the UV-1/2 test facility. It was found that parameters characterizing the synergistic effects of mass loss of the material for fixed conditions of electron-proton and combined radiations are the functions of irradiation time. To interpret the experimental data, a physical-mathematical model of mass loss of polymeric materials in vacuum was proposed. The obtained data can be explained by diffusion fluxes associated with the gradient of

  18. Mass loss of Greenland's glaciers and ice caps 2003-2008 from ICESat data

    NASA Astrophysics Data System (ADS)

    Bolch, Tobias; Sandberg Sørensen, Louise; Simonsen, Sebastian B.; Mölg, Nico; Machguth, Horst; Rastner, Philipp; Paul, Frank

    2013-04-01

    The melt water of the glaciers and ice caps (GIC) on Greenland could make a substantial contribution to global sea-level rise during this century. The recently finalized Greenland glacier inventory classified all GIC according to its connectivity to the ice sheet (CL0: no connection, CL1: weak connection, CL2: strong connection). This dataset allowed us for the first time to determine their mass changes separately from the ice sheet using space-borne laser altimetry data from the ICESat GLAS sensor. The accuracy of the altimetry measurements of about ±0.5 m even over rough surfaces along with their small footprint (about 70 m) is making them very suitable to assess elevation changes over GIC. A major challenge with ICESat data is the sparse density of the tracks (horizontal separation is about 30 km in southern and ~10 km in northern Greenland), and the fact that the repeat tracks can be several hundred metres apart. A further challenge is the volume to mass conversion. We extrapolated the elevation changes based on the glacier hypsometry and applied corrections for firn compaction and ice density based on climatic conditions. The Greenland GIC which are clearly separable from the ice-sheet (CL0, CL1) lost 30.1 ± 9.4 Gt a-1 or 0.08 ± 0.026 mm a-1 sea-level equivalent (SLE) between 2003 and 2008. When considering all hydrologically separable GIC (CL0-2, including the Geikie Plateau) the loss is 46.8 ± 13.4 Gt a-1 (0.12 ± 0.038 mm a-1 SLE). This is a significant fraction (about 20%) of the reported overall mass loss of Greenland (including the ice sheet) and up to 10% of the estimated contribution from the world's GIC to global sea-level rise. The mass loss of the GIC is per unit area about 2.5 times higher than for the ice sheet, and marine-terminating glaciers account for about half of the mass loss. The loss was highest in the south-eastern sector and lowest in the northern sector of Greenland.

  19. Using SN 1987A light echoes to determine mass loss from the progenitor

    NASA Technical Reports Server (NTRS)

    Crotts, Arlin P. S.; Kunkel, William E.

    1991-01-01

    The hypothesis that the blue progenitor of SN 1987A passed through a blue supergiant phase ending with the expulsion of the outer envelope is tested. The many light echoes seen near SN 1987A were used to search for a mass flow from the progenitor and for abrupt density changes at the limits of this smooth mass flow. The progenitor needed roughly a million yr to create these structures, assuming a constant mass loss at 15 km/s. The dust in the region is small-grained and isotropically scattering. Interaction between the progenitor blue supergiant and red supergiant winds is probably contained within a roughly spherical structure 1.5 pc in diameter.

  20. Prepregnancy and Early Adulthood Body Mass Index and Adult Weight Change in Relation to Fetal Loss

    PubMed Central

    Gaskins, Audrey J.; Rich-Edwards, Janet W.; Colaci, Daniela S.; Afeiche, Myriam C.; Toth, Thomas L.; Gillman, Matthew W.; Missmer, Stacey A.; Chavarro, Jorge E.

    2014-01-01

    Objective To examine prospectively the relationships of prepregnancy body mass index (BMI), BMI at age 18, and weight change since age 18 with risk of fetal loss. Methods Our prospective cohort study included 25,719 pregnancies reported by 17,027 women in the Nurses’ Health Study II between 1990 and 2009. In 1989, height, current weight, and weight at age 18 were self-reported. Current weight was updated every 2 years thereafter. Pregnancies were self-reported, with case pregnancies lost spontaneously and comparison pregnancies ending in ectopic pregnancy, induced abortion, or live birth. Results Incident fetal loss was reported in 4,494 (17.5%) pregnancies. Compared to those of normal BMI, the multivariate relative risk (RR) (95% confidence interval [CI]) of fetal loss was 1.07 (1.00, 1.15) for overweight women, 1.10 (0.98, 1.23) for class I obese women, and 1.27 (1.11, 1.45) for class II & III obese women (P, trend=<0.001). BMI at age 18 was not associated with fetal loss (P, trend=0.59). Compared to women who maintained a stable weight (+/− 4 kg) between age 18 and before pregnancy, women who lost weight had a 20% (95% CI 9, 29%) lower risk of fetal loss. This association was stronger among women who were overweight at age 18. Conclusion Being overweight or obese prior to pregnancy was associated with higher risk of fetal loss. In women overweight or obese at age 18, losing 4 kg or more was associated with a lower risk of fetal loss. PMID:25198273

  1. Constraints on continental crustal mass loss via chemical weathering using lithium and its isotopes

    NASA Astrophysics Data System (ADS)

    Rudnick, R. L.; Liu, X. M.

    2012-04-01

    The continental crust has an "intermediate" bulk composition that is distinct from primary melts of peridotitic mantle (basalt or picrite). This mismatch between the "building blocks" and the "edifice" that is the continental crust points to the operation of processes that preferentially remove mafic to ultramafic material from the continents. Such processes include lower crustal recycling (via density foundering or lower crustal subduction - e.g., relamination, Hacker et al., 2011, EPSL), generation of evolved melts via slab melting, and/or chemical weathering. Stable isotope systems point to the influence of chemical weathering on the bulk crust composition: the oxygen isotope composition of the bulk crust is distinctly heavier than that of primary, mantle-derived melts (Simon and Lecuyer, 2005, G-cubed) and the Li isotopic composition of the bulk crust is distinctly lighter than that of mantle-derive melts (Teng et al., 2004, GCA; 2008, Chem. Geol.). Both signatures mark the imprint of chemical weathering on the bulk crust composition. Here, we use a simple mass balance model for lithium inputs and outputs from the continental crust to quantify the mass lost due to chemical weathering. We find that a minimum of 15%, a maximum of 60%, and a best estimate of ~40% of the original juvenile rock mass may have been lost via chemical weathering. The accumulated percentage of mass loss due to chemical weathering leads to an average global chemical weathering rate (CWR) of ~ 1×10^10 to 2×10^10 t/yr since 3.5 Ga, which is about an order of magnitude higher than the minimum estimates based on modern rivers (Gaillardet et al., 1999, Chem. Geol.). While we cannot constrain the exact portion of crustal mass loss via chemical weathering, given the uncertainties of the calculation, we can demonstrate that the weathering flux is non-zero. Therefore, chemical weathering must play a role in the evolution of the composition and mass of the continental crust.

  2. The nebula around the post-AGB star 89 Herculis

    NASA Astrophysics Data System (ADS)

    Bujarrabal, V.; van Winckel, H.; Neri, R.; Alcolea, J.; Castro-Carrizo, A.; Deroo, P.

    2007-06-01

    Aims:We aim to study the structure of the nebula around the post-AGB, binary star 89 Her. The presence of a rotating disk around this star had been proposed but not been yet confirmed by observations. Methods: We present high-resolution PdBI maps of CO J=2-1 and 1-0. Properties of the nebula are directly derived from the data and model fitting. We also present N-band interferometric data on the extent of the hot dust emission, obtained with the VLTI. Results: Two nebular components are found: (a) an extended hour-glass-like structure, with expansion velocities of 7 km s-1 and a total mass 3× 10-3 M{⊙}, and (b) an unresolved very compact component, smaller than 0.4 arcsec and with a low total velocity dispersion of 5 km s-1. We cannot determine the velocity field in the compact component, but we argue that it can hardly be in expansion, since this would require too recent and too sudden an ejection of mass. On the other hand, assuming that this component is a Keplerian disk, we derive disk properties that are compatible with expectations for such a structure; in particular, the size of the rotating gas disk should be very similar to the extent of the hot dust component from our VLTI data. Assuming that the equator of the extended nebula coincides with the binary orbital plane, we provide new results on the companion star mass and orbit. Based on observations carried out with the IRAM Plateau de Bure Interferometer, as well as on observations of the Belgian Guaranteed time on VISA (ESO). IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).

  3. Determination of clothing evaporative resistance on a sweating thermal manikin in an isothermal condition: heat loss method or mass loss method?

    PubMed

    Wang, Faming; Gao, Chuansi; Kuklane, Kalev; Holmér, Ingvar

    2011-08-01

    This paper addresses selection between two calculation options, i.e heat loss option and mass loss option, for thermal manikin measurements on clothing evaporative resistance conducted in an isothermal condition (T(manikin) = T(a) = T(r)). Five vocational clothing ensembles with a thermal insulation range of 1.05-2.58 clo were selected and measured on a sweating thermal manikin 'Tore'. The reasons why the isothermal heat loss method generates a higher evaporative resistance than that of the mass loss method were thoroughly investigated. In addition, an indirect approach was applied to determine the amount of evaporative heat energy taken from the environment. It was found that clothing evaporative resistance values by the heat loss option were 11.2-37.1% greater than those based on the mass loss option. The percentage of evaporative heat loss taken from the environment (H(e,env)) for all test scenarios ranged from 10.9 to 23.8%. The real evaporative cooling efficiency ranged from 0.762 to 0.891, respectively. Furthermore, it is evident that the evaporative heat loss difference introduced by those two options was equal to the heat energy taken from the environment. In order to eliminate the combined effects of dry heat transfer, condensation, and heat pipe on clothing evaporative resistance, it is suggested that manikin measurements on the determination of clothing evaporative resistance should be performed in an isothermal condition. Moreover, the mass loss method should be applied to calculate clothing evaporative resistance. The isothermal heat loss method would appear to overestimate heat stress and thus should be corrected before use. PMID:21669906

  4. Quantifying the mass loss of peripheral Greenland glaciers and ice caps (1958-2014).

    NASA Astrophysics Data System (ADS)

    Noël, Brice; van de Berg, Willem Jan; Machguth, Horst; van den Broeke, Michiel

    2016-04-01

    Since the 2000s, mass loss from Greenland peripheral glaciers and ice caps (GICs) has accelerated, becoming an important contributor to sea level rise. Under continued warming throughout the 21st century, GICs might yield up to 7.5 to 11 mm sea level rise, with increasing dominance of surface runoff at the expense of ice discharge. However, despite multiple observation campaigns, little remains known about the contribution of GICs to total Greenland mass loss. Furthermore, the relatively coarse resolutions in regional climate models, i.e. 5 km to 20 km, fail to represent the small scale patterns of surface mass balance (SMB) components over these topographically complex regions including also narrow valley glaciers. Here, we present a novel approach to quantify the contribution of GICs to surface melt and runoff, based on an elevation dependent downscaling method. GICs daily SMB components at 1 km resolution are obtained by statistically downscaling the outputs of RACMO2.3 at 11 km resolution to a down-sampled version of the GIMP DEM for the period 1958-2014. This method has recently been successfully validated over the Greenland ice sheet and is now applied to GICs. In this study, we first evaluate the 1 km daily downscaled GICs SMB against a newly available and comprehensive dataset of ablation stake measurements. Then, we investigate present-day trends of meltwater production and SMB for different regions and estimate GICs contribution to total Greenland mass loss. These data are considered valuable for model evaluation and prediction of future sea level rise.

  5. Episodic mass loss from the hydrogen-deficient central star of the planetary nebula Longmore 4

    SciTech Connect

    Bond, Howard E.

    2014-09-01

    A spectacular transient mass-loss episode from the extremely hot, hydrogen-deficient central star of the planetary nebula (PN) Longmore 4 (Lo 4) was discovered in 1992 by Werner et al. During that event, the star temporarily changed from its normal PG 1159 spectrum to that of an emission-line low-luminosity early-type Wolf-Rayet [WCE] star. After a few days, Lo 4 reverted to its normal, predominantly absorption-line PG 1159 type. To determine whether such events recur, and if so how often, I monitored the optical spectrum of Lo 4 from early 2003 to early 2012. Out of 81 spectra taken at random dates, 4 of them revealed mass-loss outbursts similar to that seen in 1992. This indicates that the episodes recur approximately every 100 days (if the recurrence rate has been approximately constant and the duration of a typical episode is ∼5 days), and that the star is in a high-mass-loss state about 5% of the time. Since the enhanced stellar wind is hydrogen-deficient, it arises from the photosphere and is unlikely to be related to phenomena such as a binary or planetary companion or infalling dust. I speculate on plausible mechanisms for these unique outbursts, including the possibility that they are related to the non-radial GW Vir-type pulsations exhibited by Lo 4. The central star of the PN NGC 246 has stellar parameters similar to those of Lo 4, and it is also a GW Vir-type pulsator with similar pulsation periods. I obtained 167 spectra of NGC 246 between 2003 and 2011, but no mass ejections were found.

  6. Episodic Mass Loss from the Hydrogen-deficient Central Star of the Planetary Nebula Longmore 4

    NASA Astrophysics Data System (ADS)

    Bond, Howard E.

    2014-09-01

    A spectacular transient mass-loss episode from the extremely hot, hydrogen-deficient central star of the planetary nebula (PN) Longmore 4 (Lo 4) was discovered in 1992 by Werner et al. During that event, the star temporarily changed from its normal PG 1159 spectrum to that of an emission-line low-luminosity early-type Wolf-Rayet [WCE] star. After a few days, Lo 4 reverted to its normal, predominantly absorption-line PG 1159 type. To determine whether such events recur, and if so how often, I monitored the optical spectrum of Lo 4 from early 2003 to early 2012. Out of 81 spectra taken at random dates, 4 of them revealed mass-loss outbursts similar to that seen in 1992. This indicates that the episodes recur approximately every 100 days (if the recurrence rate has been approximately constant and the duration of a typical episode is ~5 days), and that the star is in a high-mass-loss state about 5% of the time. Since the enhanced stellar wind is hydrogen-deficient, it arises from the photosphere and is unlikely to be related to phenomena such as a binary or planetary companion or infalling dust. I speculate on plausible mechanisms for these unique outbursts, including the possibility that they are related to the non-radial GW Vir-type pulsations exhibited by Lo 4. The central star of the PN NGC 246 has stellar parameters similar to those of Lo 4, and it is also a GW Vir-type pulsator with similar pulsation periods. I obtained 167 spectra of NGC 246 between 2003 and 2011, but no mass ejections were found. Based on observations with the 1.5 m telescope operated by the SMARTS Consortium at Cerro Tololo Interamerican Observatory.

  7. Down-tail mass loss by plasmoids in Jupiter's and Saturn's magnetospheres

    NASA Astrophysics Data System (ADS)

    Cowley, S. W. H.; Nichols, J. D.; Jackman, C. M.

    2015-08-01

    Recent estimates of the plasma mass-loss rates by the formation and down-tail propagation of plasmoids observed in the plasma sheet in Jupiter's and Saturn's magnetosphere fall short of inner moon source rates by at least an order of magnitude. Here we argue that on the time scale between large-scale disconnection events, ~15 h at Jupiter and ~45 h at Saturn, mass-loaded closed flux tubes will typically have stretched out a few hundred planetary radii down tail at speeds ~100-200 km s-1. Consequently, the "plasmoids" of order ~10 planetary radii in length observed at closer planetary distances represent only a small planetward portion of the overall structure that is disconnected and lost down tail. Plasmoid mass-loss estimates are then revised upward by around an order of magnitude, becoming comparable to the moon source values. Additional "hidden," e.g., small-scale, mass-loss processes of comparable strength may not then be required. The essentially continuous azimuthally flowing source plasma in the dusk sector is shown to correspond to a plasma sheet layer adjacent to the magnetopause of width typically ~10% of the distance to the magnetopause in that local time sector. This physical picture also provides a simple explanation for the asymmetry in the plasmoid bipolar field signature observed at both Jupiter and Saturn and predicts that the apparent plasmoid length will increase with distance down tail to a limit beyond a few hundred planetary radii where the full ~100-200 planetary radii structures will be observed.

  8. Ultraviolet emission from main-sequence companions of AGB stars

    NASA Astrophysics Data System (ADS)

    Ortiz, Roberto; Guerrero, Martín A.

    2016-09-01

    Although the majority of known binary asymptotic giant branch (AGB) stars are symbiotic systems (i.e. with a white dwarf as a secondary star), main-sequence companions of AGB stars can be more numerous, even though they are more difficult to find because the primary high luminosity hampers the detection of the companion at visual wavelengths. However, in the ultraviolet the flux emitted by a secondary with Teff > 5500 ˜ 6000 K may prevail over that of the primary, and then it can be used to search for candidates to binary AGB stars. In this work, theoretical atmosphere models are used to calculate the UV excess in the GALEX near- and far-UV bands due to a main-sequence companion. After analysing a sample of confirmed binary AGB stars, we propose as a criterium for binarity: (1) the detection of the AGB star in the GALEX far-UV band and/or (2) a GALEX near-UV observed-to-predicted flux ratio >20. These criteria have been applied to a volume-limited sample of AGB stars within 500 pc of the Sun; 34 out of the sample of 58 AGB stars (˜60 per cent) fulfill them, implying to have a main-sequence companion of spectral type earlier than K0. The excess in the GALEX near- and far-UV bands cannot be attributed to a single temperature companion star, thus suggesting that the UV emission of the secondary might be absorbed by the extended atmosphere and circumstellar envelope of the primary or that UV emission is produced in accretion flows.

  9. The effect of tidal force and mass loss in star clusters sinking process

    NASA Astrophysics Data System (ADS)

    Matsubayashi, Tatsushi; Ebisuzaki, Toshikazu

    Compact star clusters in the star burst galaxies sink toward the galactic center through dynamical friction. If they survive well against the mass loss by the stellar evolution and the tidal stripping from the parent galaxy, then they convey intermediate mass black holes (~1000 Msolar), produced in the cluster through runaway mergings of the massive stars, into the galactic center to form a supermassive black hole (Ebisuzaki et al. 2001). In the present paper, we investigated the condition for surviving of the cluster by means of numerical simulations which include stellar evolution and tidal stripping. As stars evolve, they eject their mass, which is lost away from the cluster. Furthermore, the tidal force of the parent galaxy stripped the stars in the outside of the cluster. Through these processes, both the number of the members and the gravitational binding energy of the cluster become smaller as they sink. Finally they totally disrupted, when their identity is lost. We performed a series of the gravitational N-body simulations for the star clusters of the star burst galaxy, M82. We found that a cluster with an initial cluster mass of Mc ≥ 3×106Msolar and the lower limit mass of IMF Mmin ≤ 0.5 Msolar. The surviving condition of the cluster well survive until it sinks down to the center of the parent galaxy. We also found that the results depend strongly on the total mass of cluster and initial mass function, IMF. These results support the formation scenario of supermassive black hole described above. We adopted Hernquist spherical galaxy model for M82 Galaxy, which is truncated at galactic radius rb = 0.5 kpc and whose mass is Mb = 2.8×109Msolar and King model for the compact star cluster, whose central potential is W0 = 5.0 and core radius is r0 ~ 1pc. We used special-purpose computer, MDGRAPE-2.

  10. The rate of mass loss and variations in the wind from the Be star delta Centauri

    NASA Technical Reports Server (NTRS)

    Snow, T. P., Jr.; Oegerle, W. R.; Polidan, R. S.

    1980-01-01

    Copernicus ultraviolet scans of the Be star delta Centauri obtained in 1976 and 1979, show a significant variation in the Si III lambda 1206 profile, The strong asymmetry that was present in 1976 had disappeared by 1979. The Si IV lambda 1400 doublet was also asymmetric in 1976, but was not observed in 1979. A quantitative fit of the line shapes to theoretical wind profiles shows that the mass-loss rate in 1976 was 2 x 10 to the minus 8th power/yr, and that the rate of mass loss in Si III was at least one order of magnitude less in 1979. It is not possible to determine whether the variation represented an overall change in the lass-loss rate, or whether it was due to a change in the ionization balance. The profile fitting procedure resulted in the adoption of assumed underlying photospheric Si III and Si IV profiles, and the equivalent widths measured from these profiles are most consistent with T sub eff between 30,000 and 35,000 K, somewhat hotter than implied by the spectral classification normally assigned to this star. The ultraviolet photospheric line widths, coupled wit published theoretical analyses of rotational gravitational darkening, imply an intrinsic equatorial velocity of about 310 km/sec and an angle of inclination of the rotational axis to the line of sight of i is less than or equal to 44 deg.

  11. On the 'real' mass loss of some surging glaciers in the central Karakoram

    NASA Astrophysics Data System (ADS)

    Paul, Frank

    2016-04-01

    Several assessments of the mass changes of surging glaciers in the central Karakoram (and elsewhere) have shown near-zero changes over the typically decadal-long observation periods. This is in line with the theory that during a surge mass from a reservoir area is moved down-glacier to a receiving area with limited overall change. The resulting elevation changes of the glacier surface as determined by differencing DEMs from two points in time show a typical pattern (decreasing at higher, increasing at lower elevations) with a possible strong frontal advance (km scale) of the terminus. However, this is only half of the story as the observed mass gain at lower elevations is ultimately also a loss. This loss can only be determined when it is calculated separately and when sufficiently precise DEMs from the beginning and the end of a surge are available for each individual glacier. As the latter are hard to obtain, this study presents a simplified geomorphometric approach to approximate a potential maximum surge volume for 20 glaciers with a channel-like glacier fore field. By assuming a semi-elliptical cross-section of the channels, simple measurements of their average width, height and length in Google Earth provide the volume. Further glacier-specific parameters are taken from a recently compiled glacier inventory (area, slope) and Google Earth (minimum length and highest/lowest elevations) to obtain characteristics such as elevation ranges and volume. The average annual specific volume loss for each glacier is then determined by dividing the calculated surge volumes by the respective glacier area and the duration of a full surge cycle (obtained in a previous study). Which glacier area (minimum?) and surge duration (only the active phase?) have to be taken for this calculation is likely a matter of debate. With surge distances between about 1 and 5 km and channel widths (heights) between 300 and 700 (50 and 125) m, the surge volumes vary between 15 and 250 (mean 80

  12. Nitrogen losses from dairy manure estimated through nitrogen mass balance and chemical markers

    USGS Publications Warehouse

    Hristov, Alexander N.; Zaman, S.; Vander Pol, M.; Ndegwa, P.; Campbell, L.; Silva, S.

    2009-01-01

    Ammonia is an important air and water pollutant, but the spatial variation in its concentrations presents technical difficulties in accurate determination of ammonia emissions from animal feeding operations. The objectives of this study were to investigate the relationship between ammonia volatilization and ??15N of dairy manure and the feasibility of estimating ammonia losses from a dairy facility using chemical markers. In Exp. 1, the N/P ratio in manure decreased by 30% in 14 d as cumulative ammonia losses increased exponentially. Delta 15N of manure increased throughout the course of the experiment and ??15N of emitted ammonia increased (p < 0.001) quadratically from -31??? to -15 ???. The relationship between cumulative ammonia losses and ??15N of manure was highly significant (p < 0.001; r2 = 0.76). In Exp. 2, using a mass balance approach, approximately half of the N excreted by dairy cows (Bos taurus) could not be accounted for in 24 h. Using N/P and N/K ratios in fresh and 24-h manure, an estimated 0.55 and 0.34 (respectively) of the N excreted with feces and urine could not be accounted for. This study demonstrated that chemical markers (P, K) can be successfully used to estimate ammonia losses from cattle manure. The relationship between manure ??15N and cumulative ammonia loss may also be useful for estimating ammonia losses. Although promising, the latter approach needs to be further studied and verified in various experimental conditions and in the field. Copyright ?? 2009 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. All rights reserved.

  13. Evidence of tidal distortions and mass-loss from the old open cluster NGC 6791

    NASA Astrophysics Data System (ADS)

    Dalessandro, E.; Miocchi, P.; Carraro, G.; Jílková, L.; Moitinho, A.

    2015-05-01

    We present the first evidence of clear signatures of tidal distortions in the density distribution of the fascinating open cluster NGC 6791. We used deep and wide-field data obtained with the Canada-France-Hawaii Telescope covering a 2° × 2° area around the cluster. The 2D density map obtained with the optimal matched filter technique shows a clear elongation and an irregular distribution starting from ˜300 arcsec from the cluster centre. At larger distances, two tails extending in opposite directions beyond the tidal radius are also visible. These features are aligned to both the absolute proper motion and to the Galactic Centre directions. Moreover, other overdensities appear to be stretched in a direction perpendicular to the Galactic plane. Accordingly to the behaviour observed in the density map, we find that both the surface brightness and the star count density profiles reveal a departure from a King model starting from ˜600 arcsec from the centre. These observational evidence suggest that NGC 6791 is currently experiencing mass-loss likely due to gravitational shocking and interactions with the tidal field. We use this evidence to argue that NGC 6791 should have lost a significant fraction of its original mass. A larger initial mass would in fact explain why the cluster survived so long. Using available recipes based on analytic studies and N-body simulations, we derived the expected mass-loss due to stellar evolution and tidal interactions and estimated the initial cluster mass to be Mini = (1.5-4) × 105 M⊙.

  14. Allocation of extracellular enzymatic activity in relation to litter composition, N deposition, and mass loss

    USGS Publications Warehouse

    Sinsabaugh, R. L.; Carreiro, M.M.; Repert, D.A.

    2002-01-01

    Decomposition of plant material is a complex process that requires interaction among a diversity of microorganisms whose presence and activity is subject to regulation by a wide range of environmental factors. Analysis of extracellular enzyme activity (EEA) provides a way to relate the functional organization of microdecomposer communities to environmental variables. In this study, we examined EEA in relation to litter composition and nitrogen deposition. Mesh bags containing senescent leaves of Quercus borealis (red oak), Acer rubrum (red maple) and Cornus florida (flowering dogwood) were placed on forest floor plots in southeastern New York. One-third of the plots were sprayed monthly with distilled water. The other plots were sprayed monthly with NH4NO3 solution at dose rates equivalent to 2 or 8 g N m-2 y-1. Mass loss, litter composition, fungal mass, and the activities of eight enzymes were measured on 13 dates for each litter type. Dogwood was followed for one year, maple for two, oak for three, For each litter type and treatment, enzymatic turnover activities were calculated from regressions of LN (%mass remaining) vs. cumulative activity. The decomposition of dogwood litter was more efficient than that of maple and oak. Maple litter had the lowest fungal mass and required the most enzymatic work to decompose, even though its mass loss rate was twice that of oak. Across litter types, N amendment reduced apparent enzymatic efficiencies and shifted EEA away from N acquisition and toward P acquisition, and away from polyphenol oxidation and toward polysaccharide hydrolysis. The effect of these shifts on decomposition rate varied with litter composition: dogwood was stimulated, oak was inhibited and maple showed mixed effects. The results show that relatively small shifts in the activity of one or two critical enzymes can significantly alter decomposition rates.

  15. Copernicus ultraviolet observations of mass-loss effects in O and B stars

    NASA Technical Reports Server (NTRS)

    Snow, T. P., Jr.; Morton, D. C.

    1976-01-01

    Far-UV spectra of 47 O, B, and A stars obtained with the Copernicus satellite are examined for P Cygni profiles. For all 40 stars with displaced absorption lines, values are given for the velocities of the short-wavelength edge, the line center, and the emission peak (if present). Parts of the spectra of 42 stars are reproduced, evidence for mass motions in ground-based spectra is discussed, and the best available data are summarized on the wavelengths and oscillator strengths of most lines likely to show mass-loss effects in either visual or UV spectra. The main conclusions are that: (1) the far-UV transitions, especially resonance lines, show that mass flow is present over a much wider group of stars than revealed by visible data on subordinate lines; (2) most of the line shifts imply mass motion away from the stars; (3) mass flow occurs in all but one star brighter than a bolometric magnitude of -6.0; and (4) the observed terminal velocities generally exhibit no significant correlation with temperature, luminosity, gravity, rotational velocity, or line strength.

  16. Substantial glacier mass loss in the Tien Shan over the past 50 years

    NASA Astrophysics Data System (ADS)

    Farinotti, Daniel; Longuevergne, Laurent; Moholdt, Geir; Duethmann, Doris; Mölg, Thomas; Bolch, Tobias; Vorogushyn, Sergiy; Güntner, Andreas

    2015-09-01

    Populations in Central Asia are heavily dependent on snow and glacier melt for their water supplies. Changes to the glaciers in the main mountain range in this region, the Tien Shan, have been reported over the past decade. However, reconstructions over longer, multi-decadal timescales and the mechanisms underlying these variations--both required for reliable future projections--are not well constrained. Here we use three ensembles of independent approaches based on satellite gravimetry, laser altimetry, and glaciological modelling to estimate the total glacier mass change in the Tien Shan. Results from the three approaches agree well, and allow us to reconstruct a consistent time series of annual mass changes for the past 50 years at the resolution of individual glaciers. We detect marked spatial and temporal variability in mass changes. We estimate the overall decrease in total glacier area and mass from 1961 to 2012 to be 18 +/- 6% and 27 +/- 15%, respectively. These values correspond to a total area loss of 2,960 +/- 1,030 km2, and an average glacier mass-change rate of -5.4 +/- 2.8 Gt yr-1. We suggest that the decline is driven primarily by summer melt and, possibly, linked to the combined effects of general climatic warming and circulation variability over the north Atlantic and north Pacific.

  17. Gas Loss by Ram Pressure Stripping and Internal Feedback from Low-mass Milky Way Satellites

    NASA Astrophysics Data System (ADS)

    Emerick, Andrew; Mac Low, Mordecai-Mark; Grcevich, Jana; Gatto, Andrea

    2016-08-01

    The evolution of dwarf satellites in the Milky Way (MW) is affected by a combination of ram pressure stripping (RPS), tidal stripping, and internal feedback from massive stars. We investigate gas loss processes in the smallest satellites of the MW using three-dimensional, high-resolution, idealized wind tunnel simulations, accounting for gas loss through both ram pressure stripping and expulsion by supernova feedback. Using initial conditions appropriate for a dwarf galaxy like Leo T, we investigate whether or not environmental gas stripping and internal feedback can quench these low-mass galaxies on the expected timescales, shorter than 2 Gyr. We find that supernova feedback contributes negligibly to the stripping rate for these low star formation rate galaxies. However, we also find that RPS is less efficient than expected in the stripping scenarios we consider. Our work suggests that although RPS can eventually completely strip these galaxies, other physics is likely at play to reconcile our computed stripping times with the rapid quenching timescales deduced from observations of low-mass MW dwarf galaxies. We discuss the roles additional physics may play in this scenario, including host-satellite tidal interactions, cored versus cuspy dark matter profiles, reionization, and satellite preprocessing. We conclude that a proper accounting of these physics together is necessary to understand the quenching of low-mass MW satellites.

  18. Mass loss of shuttle space suit orthofabric under simulated ionospheric atomic oxygen bombardment

    NASA Technical Reports Server (NTRS)

    Miller, W. L.

    1985-01-01

    Many polymeric materials used for thermal protection and insulation on spacecraft degrade significantly under prolonged bombardment by ionospheric atomic oxygen. The covering fabric of the multilayered shuttle space suit is composed of a loose weave of GORE-TEX fibers, Nomex and Kevlar-29, which are all polymeric materials. The complete evaluation of suit fabric degradation from ionospheric atomic oxygen is of importance in reevaluating suit lifetime and inspection procedures. The mass loss and visible physical changes of each test sample was determined. Kapton control samples and data from previous asher and flight tests were used to scale the results to reflect ionospheric conditions at about 220 km altitude. It is predicted that the orthofabric loses mass in the ionosphere at a rate of about 66% of the original orthofabric mass/yr. The outer layer of the two-layer orthofabric test samples shows few easily visible signs of degradation, even when observed at 440X. It is concluded that the orthofabric could suffer significant loss of performance after much less than a year of total exposure time, while the degradation might be undetectable in post flight visual examinations of space suits.

  19. Loss of muscle mass: current developments in cachexia and sarcopenia focused on biomarkers and treatment

    PubMed Central

    Drescher, Cathleen; Konishi, Masaaki; Ebner, Nicole; Springer, Jochen

    2015-01-01

    Loss of muscle mass arises from an imbalance of protein synthesis and protein degradation. Potential triggers of muscle wasting and function are immobilization, loss of appetite, dystrophies, and chronic diseases as well as aging. All these conditions lead to increased morbidity and mortality in patients, which makes it a timely matter to find new biomarkers to get a fast clinical diagnosis and to develop new therapies. This mini-review covers current developments in the field of biomarkers and drugs on cachexia and sarcopenia. Here, we reported about promising markers, e.g. tartate-resistant acid phosphatase 5a, and novel substances like epigallocatechin-3-gallate. In summary, the progress to combat muscle wasting is in full swing, and perhaps diagnosis of muscle atrophy and of course patient treatments could be soon support by improved and more helpful strategies. PMID:26676067

  20. Equation of motion of an interstellar Bussard ramjet with radiation and mass losses

    NASA Astrophysics Data System (ADS)

    Semay, Claude; Silvestre-Brac, Bernard

    2008-11-01

    An interstellar Bussard ramjet is a spaceship using the protons of the interstellar medium in a fusion engine to produce thrust. In recent papers, it was shown that the relativistic equation of motion of an ideal ramjet and that of a ramjet with radiation loss are analytical. When a mass loss appears, the limit speed of the ramjet is more strongly reduced. However, the parametric equations in terms of the ramjet's speed for the position of the ramjet in the inertial frame of the interstellar medium, the time in this frame and the proper time indicated by the clocks on board the spaceship can still be obtained in an analytical form. The non-relativistic motion and the motion near the limit speed are studied.

  1. Loss of muscle mass: current developments in cachexia and sarcopenia focused on biomarkers and treatment.

    PubMed

    Drescher, Cathleen; Konishi, Masaaki; Ebner, Nicole; Springer, Jochen

    2015-12-01

    Loss of muscle mass arises from an imbalance of protein synthesis and protein degradation. Potential triggers of muscle wasting and function are immobilization, loss of appetite, dystrophies, and chronic diseases as well as aging. All these conditions lead to increased morbidity and mortality in patients, which makes it a timely matter to find new biomarkers to get a fast clinical diagnosis and to develop new therapies. This mini-review covers current developments in the field of biomarkers and drugs on cachexia and sarcopenia. Here, we reported about promising markers, e.g. tartate-resistant acid phosphatase 5a, and novel substances like epigallocatechin-3-gallate. In summary, the progress to combat muscle wasting is in full swing, and perhaps diagnosis of muscle atrophy and of course patient treatments could be soon support by improved and more helpful strategies. PMID:26676067

  2. Loss of muscle mass: Current developments in cachexia and sarcopenia focused on biomarkers and treatment.

    PubMed

    Drescher, Cathleen; Konishi, Masaaki; Ebner, Nicole; Springer, Jochen

    2016-01-01

    Loss of muscle mass arises from an imbalance of protein synthesis and protein degradation. Potential triggers of muscle wasting and function are immobilization, loss of appetite, dystrophies and chronic diseases as well as aging. All these conditions lead to increased morbidity and mortality in patients, which makes it a timely matter to find new biomarkers to get a fast clinical diagnosis and to develop new therapies. This mini-review covers current developments in the field of biomarkers and drugs on cachexia and sarcopenia. Here, we reported about promising markers, e.g. tartrate-resistant acid phosphatase 5a (TRACP5a), and novel substances like Epigallocatechin-3-gallate (EGCg). In summary, the progress to combat muscle wasting is in full swing and perhaps diagnosis of muscle atrophy and of course patient treatments could be soon supported by improved and more helpful strategies. PMID:26474466

  3. Parkin loss leads to PARIS-dependent declines in mitochondrial mass and respiration.

    PubMed

    Stevens, Daniel A; Lee, Yunjong; Kang, Ho Chul; Lee, Byoung Dae; Lee, Yun-Il; Bower, Aaron; Jiang, Haisong; Kang, Sung-Ung; Andrabi, Shaida A; Dawson, Valina L; Shin, Joo-Ho; Dawson, Ted M

    2015-09-15

    Mutations in parkin lead to early-onset autosomal recessive Parkinson's disease (PD) and inactivation of parkin is thought to contribute to sporadic PD. Adult knockout of parkin in the ventral midbrain of mice leads to an age-dependent loss of dopamine neurons that is dependent on the accumulation of parkin interacting substrate (PARIS), zinc finger protein 746 (ZNF746), and its transcriptional repression of PGC-1α. Here we show that adult knockout of parkin in mouse ventral midbrain leads to decreases in mitochondrial size, number, and protein markers consistent with a defect in mitochondrial biogenesis. This decrease in mitochondrial mass is prevented by short hairpin RNA knockdown of PARIS. PARIS overexpression in mouse ventral midbrain leads to decreases in mitochondrial number and protein markers and PGC-1α-dependent deficits in mitochondrial respiration. Taken together, these results suggest that parkin loss impairs mitochondrial biogenesis, leading to declining function of the mitochondrial pool and cell death. PMID:26324925

  4. Methane output of tortoises: its contribution to energy loss related to herbivore body mass.

    PubMed

    Franz, Ragna; Soliva, Carla R; Kreuzer, Michael; Hatt, Jean-Michel; Furrer, Samuel; Hummel, Jürgen; Clauss, Marcus

    2011-01-01

    An increase in body mass (M) is traditionally considered advantageous for herbivores in terms of digestive efficiency. However, recently increasing methane losses with increasing M were described in mammals. To test this pattern in non-mammal herbivores, we conducted feeding trails with 24 tortoises of various species (M range 0.52-180 kg) fed a diet of grass hay ad libitum and salad. Mean daily dry matter and gross energy intake measured over 30 consecutive days scaled to M(0.75 (95%CI 0.64-0.87)) and M(0.77 (95%CI 0.66-0.88)), respectively. Methane production was measured over two consecutive days in respiration chambers and scaled to M(1.03 (95%CI 0.84-1.22)). When expressed as energy loss per gross energy intake, methane losses scaled to 0.70 (95%CI 0.47-1.05) M(0.29 (95%CI 0.14-0.45)). This scaling overlaps in its confidence intervals to that calculated for nonruminant mammals 0.79 (95%CI 0.63-0.99) M(0.15 (95%CI 0.09-0.20)), but is lower than that for ruminants. The similarity between nonruminant mammals and tortoises suggest a common evolution of the gut fauna in ectotherms and endotherms, and that the increase in energetic losses due to methane production with increasing body mass is a general allometric principle in herbivores. These findings add evidence to the view that large body size itself does not necessarily convey a digestive advantage. PMID:21408074

  5. Minimalist coupled evolution model for stellar X-ray activity, rotation, mass loss, and magnetic field

    NASA Astrophysics Data System (ADS)

    Blackman, Eric G.; Owen, James E.

    2016-05-01

    Late-type main-sequence stars exhibit an X-ray to bolometric flux ratio that depends on {tilde{R}o}, the ratio of rotation period to convective turnover time, as {tilde{R}o}^{-ζ } with 2 ≤ ζ ≤ 3 for {tilde{R}o} > 0.13, but saturates with |ζ| < 0.2 for {tilde{R}o} < 0.13. Saturated stars are younger than unsaturated stars and show a broader spread of rotation rates and X-ray activity. The unsaturated stars have magnetic fields and rotation speeds that scale roughly with the square root of their age, though possibly flattening for stars older than the Sun. The connection between faster rotators, stronger fields, and higher activity has been established observationally, but a theory for the unified time-evolution of X-ray luminosity, rotation, magnetic field and mass loss that captures the above trends has been lacking. Here we derive a minimalist holistic framework for the time evolution of these quantities built from combining a Parker wind with new ingredients: (1) explicit sourcing of both the thermal energy launching the wind and the X-ray luminosity via dynamo produced magnetic fields; (2) explicit coupling of X-ray activity and mass-loss saturation to dynamo saturation (via magnetic helicity build-up and convection eddy shredding); (3) use of coronal equilibrium to determine how magnetic energy is divided into wind and X-ray contributions. For solar-type stars younger than the Sun, we infer conduction to be a subdominant power loss compared to X-rays and wind. For older stars, conduction is more important, possibly quenching the wind and reducing angular momentum loss. We focus on the time evolution for stars younger than the Sun, highlighting what is possible for further generalizations. Overall, the approach shows promise towards a unified explanation of all of the aforementioned observational trends.

  6. Exercise associated hormonal signals as powerful determinants of an effective fat mass loss.

    PubMed

    Bajer, B; Vlcek, M; Galusova, A; Imrich, R; Penesova, A

    2015-07-01

    Obesity management for achieving an effective weight loss includes dietary modification and exercise [resistance (strength), endurance (cardiovascular) or intervals training (high-intensity intermittent exercise)]. Regular exercise acutely increases fat oxidation, which induces loss of fat mass and increases energy expenditure. Moreover, it has a positive effect on the physical (improved insulin sensitivity, lipid profile, etc.) and mental health (mood, cognition, memory, sleep, etc.). Endocrine responses to muscle actions are affected by many factors, including the exercise muscle groups (lower and upper body), load/volume, time-under tension, and rest-period intervals between sets, training status, gender, and age. The aim of this review is to summarize, evaluate, and clarify the literature data focusing on the endocrine responses to different types of exercise, including the frequency, intensity, and type of movement with regard to the fat loss strategies. Many studies have investigated anabolic [growth hormone, insulin-like growth factor-1 (IGF-1), testosterone] and gluco- and appetite- regulatory (insulin, cortisol, ghrelin) hormone responses and adaptations of skeletal muscles to exercise. Muscle tissue is a critical endocrine organ, playing important role in the regulation of several physiological and metabolic events. Moreover, we are also describing the response of some other substances to exercise, such as myokines [irisin, apelin, brain-derived neurotrophic factor (BDNF), myostatin, and fibroblast growth factor 21 (FGF21)]. It is proposed that reducing intra-abdominal fat mass and increasing cardiorespiratory fitness through improving nutritional quality, reducing sedentary behavior, and increase the participation in physical activity/exercise, might be associated with clinical benefits, sometimes even in the absence of weight loss. PMID:26238498

  7. Generating Porosity in the Critical Zone: Does Volumetric Strain Dominate Chemical Mass Loss?

    NASA Astrophysics Data System (ADS)

    Hayes, J. L.; Riebe, C. S.; Holbrook, W. S.; Hartsough, P. C.

    2015-12-01

    The opening of pore space by weathering near Earth's surface influences a broad array of hydrological and biogeochemical processes, including water storage, surface-groundwater interactions, and nutrient cycling. Understanding how porosity is generated by physical and chemical processes is therefore a fundamental challenge in critical zone science. However, the relative importance and spatial variability of mechanisms that generate porosity remain poorly understood, because the subsurface is hidden from direct observation except by drilling and geophysical measurements. Here we use observations from both drilling and geophysics to quantify the relative importance of volumetric strain and chemical mass loss in the Southern Sierra Critical Zone Observatory. Our results from cores of saprolite show that porosity decreases with depth from 0.65 to 0.35 in the top 11 meters of saprolite. Although seismic refraction surveys reveal velocities that correctly predict the porosity variations, they cannot distinguish between volumetric strain and chemical mass losses. To overcome this limitation, we quantified bulk density and immobile element concentrations in our samples of saprolite. We found that volumetric strain decreases with depth from 1.1 to 0.3. Conversely, the overall mass loss due to chemical weathering shows no trend with depth. Together these results suggest that the changes in porosity are due to physical rather than chemical processes in the upper 11 meters. However neither bioturbation nor frost cracking are likely to extend so deep. Moreover, the paucity of hydrous minerals in the bedrock implies that mineral expansion cannot explain the high volumetric strain in the saprolite. Our results are consistent with porosity generated by the opening of fractures due to the release of confining stress during exhumation of bedrock.

  8. Mass Losses Of Co, Cs And Hcn On Jupiter/sl9

    NASA Astrophysics Data System (ADS)

    Moreno, Raphael; Marten, A.

    2006-09-01

    Since comet Shoemaker-Levy 9 (SL9) collided with Jupiter in 1994, the IRAM 30-m Telescope (Pico Veleta, Spain) and the 15-m JCMT (Mauna Kea,Hawaii) have regularly observed Jupiter at millimeter/submillimeter wavelengths. Molecular trace species such as HCN, CO, CS and their isotopomers have been detected in the upper atmosphere since the collision. Because of the high spectral resolution attained, our data allow one to infer both temperature and abundances in Jupiter's stratosphere with a maximum spatial resolution of 10 arcsec. We have used all these data to monitor the latitudinal spreading since the impacts occurred (Marten et al. 1995), to look for changes in their abundances with time (Moreno et al. 2001, 2003) and to determine several isotopic ratios (Matthews et al. 2002). Data taken in 2004 have shown that latitudinal distributions of all these species were almost homogeneous 10 years after impacts, as predicted by Moreno et al. 2003. Moreover, compared to 1998 results, respective mass loss factors as high as 2-7 have been determined for the three molecular main compounds (Moreno et al. 2005). In order to follow-up our monitoring, new disk mapping observations took place in May 2006 using the IRAM-30m Telescope. Here we report the results of the recent measurements of CO, CS and HCN, and also the search for new species: H2CO, H2CS, CH3CN, CH3OH. Such trace compounds could have explained the mass losses observed in 2004, but no clear detections have been obtained after reasonable integration times. Estimates of the new CO, CS and HCN total masses and upper limits for the trace species searched for will be presented. The loss mechanisms will be discussed. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).

  9. Mass loss of a TEOS-coated, reinforced carbon-carbon composite subjected to a simulted shuttle entry environment

    NASA Technical Reports Server (NTRS)

    Stroud, C. W.; Rummler, D. R.

    1980-01-01

    Coated, reinforced carbon-carbon (RCC) is used for the leading edges of the space shuttle. The mass loss characteristics of RCC specimens coated with tetraethyl orthosilicate (TEOS) were determine for conditions which simulated the environment expected at the lug attachment area of the leading edge. Mission simulation included simultaneous application of load, temperature, and oxygen partial pressure. Maximum specimen temperature was 900 K (1160 F). Specimens were exposed for up to 80 simulated missions. Stress levels up to 6.8 MPa (980 psi) did not significantly affect the mass loss characteristics of the TEOS-coated RCC material. Mass loss was correlated with the bulk density of the specimens.

  10. Study of mass loss of spacecraft polymeric thermal control coatings under electron and proton radiations

    NASA Astrophysics Data System (ADS)

    Khasanshin, Rashid; Novikov, Lev; Galygin, Alexander

    Polymeric composites have a number of properties that give a possibility to apply them as spacecraft external coatings. In space environment, however, such materials become one of the main sources of volatile products that form the outer spacecraft atmosphere and are able to con-dense on contamination-sensitive surfaces of onboard equipment. Thermal control coatings oc-cupy a considerable part of a satellite surface and are mostly subjected to ionizing radiations ac-companying by outgassing. The main stages of the process are the following: formation of vola-tile radiolysis products, diffusion of the products to free material surface, and desorption. Radia-tion-induced destruction and outgassing of material increase its permeability and accelerate mi-gration processes in it. Experimental data of effect of radiation on mass loss of polymeric composites used as thermal control coatings was analyzed and interpreted in the work. As a particular case, it was shown that mass loss of a polymeric composite irradiated by protons is greater than by electrons if energies and flux densities of the particles are the same. It can be explained that volatile products, in the first case, generate within a thin near-surface layer of material which permeability increases together with the absorbed dose, and quickly escape in vacuum. In the second case, a bulk of volatile products emerges far enough from the free surface of material which permeability increases slower as compared with proton radiation. Therefore, migration time of volatile products to the free surface grows and quantity of chemical reactions which they are involved in increases. To analyze and interpret experimental data, a mathematical model describing mass loss of polymeric composites subject to its growth of permeability under radiation is proposed. Based upon analysis of experiments and numerical simulation results, thresholds of fluen-cies and flux densities of electron and proton were determined. Exceeding these

  11. The Spontaneous Loss of Coherence Catastrophe in Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

    PubMed Central

    Aizikov, Konstantin; Mathur, Raman; O’Connor, Peter B.

    2009-01-01

    The spontaneous loss of coherence catastrophe (SLCC) is a frequently observed, yet poorly studied, space-charge related effect in Fourier-transform ion cyclotron resonance mass spectrometry (FTICR-MS). This manuscript presents an application of the filter diagonalization method (FDM) in the analysis of this phenomenon. The temporal frequency behavior reproduced by frequency shift analysis using the FDM shows the complex nature of the SLCC, which can be explained by a combination of factors occurring concurrently, governed by electrostatics and ion packet trajectories inside the ICR cell. PMID:19013078

  12. Mass-loss evolution of close-in exoplanets: Evaporation of hot Jupiters and the effect on population

    SciTech Connect

    Kurokawa, H.; Nakamoto, T.

    2014-03-01

    During their evolution, short-period exoplanets may lose envelope mass through atmospheric escape owing to intense X-ray and extreme ultraviolet (XUV) radiation from their host stars. Roche-lobe overflow induced by orbital evolution or intense atmospheric escape can also contribute to mass loss. To study the effects of mass loss on inner planet populations, we calculate the evolution of hot Jupiters considering mass loss of their envelopes and thermal contraction. Mass loss is assumed to occur through XUV-driven atmospheric escape and the following Roche-lobe overflow. The runaway effect of mass loss results in a dichotomy of populations: hot Jupiters that retain their envelopes and super Earths whose envelopes are completely lost. Evolution primarily depends on the core masses of planets and only slightly on migration history. In hot Jupiters with small cores (≅ 10 Earth masses), runaway atmospheric escape followed by Roche-lobe overflow may create sub-Jupiter deserts, as observed in both mass and radius distributions of planetary populations. Comparing our results with formation scenarios and observed exoplanets populations, we propose that populations of closely orbiting exoplanets are formed by capturing planets at/inside the inner edges of protoplanetary disks and subsequent evaporation of sub-Jupiters.

  13. The role of stellar mass-loss in dynamics of spiral galaxies

    NASA Astrophysics Data System (ADS)

    Jungwiert, B.; Combes, F.; Palous, J.

    A new N-body sticky-particles computer code for spiral galaxies is presented. The substantial improvement over existing models, either sticky-particles or SPH, is the scheme for the bi-directional mass exchange between gas and stars: the consumption of the former by star formation is taken into account by locking a fraction of gas in newly created stars while the mass-loss from stars via stellar winds and supernova explosions is implemented as time dependent over the Hubble time. A comparison with models not including gas recycling or treating it as immediate shows important differences as to star formation rate, gas consumption time, and the rate at which gas is fuelled towards galactic centers, all having potentially deep consequences for galactic evolution.

  14. Spatial and temporal distribution of mass loss from the Greenland Ice Sheet since AD 1900.

    PubMed

    Kjeldsen, Kristian K; Korsgaard, Niels J; Bjørk, Anders A; Khan, Shfaqat A; Box, Jason E; Funder, Svend; Larsen, Nicolaj K; Bamber, Jonathan L; Colgan, William; van den Broeke, Michiel; Siggaard-Andersen, Marie-Louise; Nuth, Christopher; Schomacker, Anders; Andresen, Camilla S; Willerslev, Eske; Kjær, Kurt H

    2015-12-17

    The response of the Greenland Ice Sheet (GIS) to changes in temperature during the twentieth century remains contentious, largely owing to difficulties in estimating the spatial and temporal distribution of ice mass changes before 1992, when Greenland-wide observations first became available. The only previous estimates of change during the twentieth century are based on empirical modelling and energy balance modelling. Consequently, no observation-based estimates of the contribution from the GIS to the global-mean sea level budget before 1990 are included in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Here we calculate spatial ice mass loss around the entire GIS from 1900 to the present using aerial imagery from the 1980s. This allows accurate high-resolution mapping of geomorphic features related to the maximum extent of the GIS during the Little Ice Age at the end of the nineteenth century. We estimate the total ice mass loss and its spatial distribution for three periods: 1900-1983 (75.1 ± 29.4 gigatonnes per year), 1983-2003 (73.8 ± 40.5 gigatonnes per year), and 2003-2010 (186.4 ± 18.9 gigatonnes per year). Furthermore, using two surface mass balance models we partition the mass balance into a term for surface mass balance (that is, total precipitation minus total sublimation minus runoff) and a dynamic term. We find that many areas currently undergoing change are identical to those that experienced considerable thinning throughout the twentieth century. We also reveal that the surface mass balance term shows a considerable decrease since 2003, whereas the dynamic term is constant over the past 110 years. Overall, our observation-based findings show that during the twentieth century the GIS contributed at least 25.0 ± 9.4 millimetres of global-mean sea level rise. Our result will help to close the twentieth-century sea level budget, which remains crucial for evaluating the reliability of models used to

  15. Spatial and temporal distribution of mass loss from the Greenland Ice Sheet since AD 1900

    NASA Astrophysics Data System (ADS)

    Kjeldsen, Kristian K.; Korsgaard, Niels J.; Bjørk, Anders A.; Khan, Shfaqat A.; Box, Jason E.; Funder, Svend; Larsen, Nicolaj K.; Bamber, Jonathan L.; Colgan, William; van den Broeke, Michiel; Siggaard-Andersen, Marie-Louise; Nuth, Christopher; Schomacker, Anders; Andresen, Camilla S.; Willerslev, Eske; Kjær, Kurt H.

    2015-12-01

    The response of the Greenland Ice Sheet (GIS) to changes in temperature during the twentieth century remains contentious, largely owing to difficulties in estimating the spatial and temporal distribution of ice mass changes before 1992, when Greenland-wide observations first became available. The only previous estimates of change during the twentieth century are based on empirical modelling and energy balance modelling. Consequently, no observation-based estimates of the contribution from the GIS to the global-mean sea level budget before 1990 are included in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Here we calculate spatial ice mass loss around the entire GIS from 1900 to the present using aerial imagery from the 1980s. This allows accurate high-resolution mapping of geomorphic features related to the maximum extent of the GIS during the Little Ice Age at the end of the nineteenth century. We estimate the total ice mass loss and its spatial distribution for three periods: 1900-1983 (75.1 ± 29.4 gigatonnes per year), 1983-2003 (73.8 ± 40.5 gigatonnes per year), and 2003-2010 (186.4 ± 18.9 gigatonnes per year). Furthermore, using two surface mass balance models we partition the mass balance into a term for surface mass balance (that is, total precipitation minus total sublimation minus runoff) and a dynamic term. We find that many areas currently undergoing change are identical to those that experienced considerable thinning throughout the twentieth century. We also reveal that the surface mass balance term shows a considerable decrease since 2003, whereas the dynamic term is constant over the past 110 years. Overall, our observation-based findings show that during the twentieth century the GIS contributed at least 25.0 ± 9.4 millimetres of global-mean sea level rise. Our result will help to close the twentieth-century sea level budget, which remains crucial for evaluating the reliability of models used to

  16. A HIFI view on circumstellar H2O in M-type AGB stars: radiative transfer, velocity profiles, and H2O line cooling

    NASA Astrophysics Data System (ADS)

    Maercker, M.; Danilovich, T.; Olofsson, H.; De Beck, E.; Justtanont, K.; Lombaert, R.; Royer, P.

    2016-06-01

    Aims: We aim to constrain the temperature and velocity structures, and H2O abundances in the winds of a sample of M-type asymptotic giant branch (AGB) stars. We further aim to determine the effect of H2O line cooling on the energy balance in the inner circumstellar envelope. Methods: We use two radiative-transfer codes to model molecular emission lines of CO and H2O towards four M-type AGB stars. We focus on spectrally resolved observations of CO and H2O from HIFI aboard the Herschel Space Observatory. The observations are complemented by ground-based CO observations, and spectrally unresolved CO and H2O observations with PACS aboard Herschel. The observed line profiles constrain the velocity structure throughout the circumstellar envelopes (CSEs), while the CO intensities constrain the temperature structure in the CSEs. The H2O observations constrain the o-H2O and p-H2O abundances relative to H2. Finally, the radiative-transfer modelling allows to solve the energy balance in the CSE, in principle including also H2O line cooling. Results: The fits to the line profiles only set moderate constraints on the velocity profile, indicating shallower acceleration profiles in the winds of M-type AGB stars than predicted by dynamical models, while the CO observations effectively constrain the temperature structure. Including H2O line cooling in the energy balance was only possible for the low-mass-loss-rate objects in the sample, and required an ad hoc adjustment of the dust velocity profile in order to counteract extreme cooling in the inner CSE. H2O line cooling was therefore excluded from the models. The constraints set on the temperature profile by the CO lines nevertheless allowed us to derive H2O abundances. The derived H2O abundances confirm previous estimates and are consistent with chemical models. However, the uncertainties in the derived abundances are relatively large, in particular for p-H2O, and consequently the derived o/p-H2O ratios are not well constrained.

  17. The effects in humans of rapid loss of body mass on a boxing-related task.

    PubMed

    Smith, M S; Dyson, R; Hale, T; Harrison, J H; McManus, P

    2000-09-01

    The physiological effects of strategies for a rapid loss of body mass immediately before weighing-in for competition in weight-governed sports are unclear. This study examined the effects of a 3%-4% loss in body mass on a boxing-related task. Seven novice amateur boxers completed three 3 min rounds of simulated boxing on a prototype boxing ergometer in an euhydrated state (E-trial) and after exercise-induced thermal dehydration (D-trial). All subjects lost body mass following dehydration-mean body mass fell 3.8 (SD +/- 0.3)% [77.3 (SD +/- 11.3) to 74.4 (SD +/- 10.7) kg, P<0.001] - but changes in plasma volume (PV) were inconsistent. Four subjects suffered reductions in PV between 15% and 30%, one subject maintained his E-trial value and two recorded an increase. The D-trial mean PV value was 8.0 (SD +/- 17.2)% lower but this fall was not statistically significant (P>0.05). Analysis of D-trial boxing performance showed one subject maintained his performance over the two trials and a second improved 17.8%. A two-way ANOVA (condition x time) with repeated measures on both factors showed no significant main effect differences for condition (F1,6 = 3.93 P>0.05), time (F1.83,48 = 1.12, P>0.05) or interaction between them (F1.93,48, P>0.05). Furthermore, neither heart rate nor blood lactate responses in the boxing task differed between trials. These data were affected by the small sample. Power and effect size analysis using eta(2) procedure and removing the outlier data produced a mean fall in boxing performance of 26.8%. However, some subjects appeared able to resist the deleterious effects of a rapid loss of body mass prior to competition and further research is needed to explain the mechanisms under-pinning this ability. PMID:11072771

  18. The role of pyridoxine as a countermeasure for in-flight loss of lean body mass

    NASA Technical Reports Server (NTRS)

    Gilbert, Joyce A.

    1992-01-01

    Ground based and in flight research has shown that humans, under conditions of microgravity, sustain a loss of lean body tissue (protein) and changes in several biological processes including, reductions in red blood cell mass, and neurotransmitters. The maintenance of muscle mass, the major component of lean body mass, is required to meet the needs of space station EVAs. Central to the biosynthesis of amino acids, the building blocks of protein, is pyridoxine (vitamin B-6). Muscle mass integrity requires the availability of vitamin B-6 for protein metabolism and neurotransmitter synthesis. Furthermore, the formation of red blood cells require pyridoxine as a cofactor in the biosynthesis of hemoglobin, a protein that carries oxygen to tissues. In its active form, pyridoxal-5'-phosphate (PLP), vitamin B-6 serves as a link between amino acid and carbohydrate metabolism through intermediates of glycolysis and the tricarboxylic acid cycle. In addition to its role in energy metabolism, PLP is involved in the biosynthesis of hemoglobin and neurotransmitter which are necessary for neurological functions. Alterations in pyridoxine metabolism may affect countermeasures designed to overcome some of these biochemical changes. The focus of this research is to determine the effects of microgravity on the metabolic utilization of vitamin B-6, integrating nutrition as an integral component of the countermeasure (exercise) to maintain lean body mass and muscle strength. The objectives are: 1) to determine whether microgravity effects the metabolic utilization of pyridoxine and 2) to quantitate changes in B-6 vitamer distribution in tissue and excreta relative to loss of lean body tissue. The rationale for this study encompasses the unique challenge to control biochemical mechanisms effected during space travel and the significance of pyridoxine to maintain and counter muscle integrity for EVA activities. This experiment will begin to elucidate the importance of biochemical

  19. Large-scale environments of binary AGB stars probed by Herschel. I. Morphology statistics and case studies of R Aquarii and W Aquilae

    NASA Astrophysics Data System (ADS)

    Mayer, A.; Jorissen, A.; Kerschbaum, F.; Ottensamer, R.; Nowotny, W.; Cox, N. L. J.; Aringer, B.; Blommaert, J. A. D. L.; Decin, L.; van Eck, S.; Gail, H.-P.; Groenewegen, M. A. T.; Kornfeld, K.; Mecina, M.; Posch, Thomas; Vandenbussche, B.; Waelkens, C.

    2013-01-01

    The Mass loss of Evolved StarS (MESS) sample offers a selection of 78 asymptotic giant branch (AGB) stars and red supergiants (RSGs) observed with the PACS photometer on-board Herschel at 70 μm and 160 μm. For most of these objects, the dusty AGB wind is not spherically symmetric and the wind shape can be subdivided into four classes. In the present paper we concentrate on the influence of a companion on the morphology of the stellar wind. Literature was searched to find binaries in the MESS sample, which were subsequently linked to their wind-morphology class to assert that the binaries are not distributed equally among the classes. In the second part of the paper we concentrate on the circumstellar environment of the two prominent objects R Aqr and W Aql. Each shows a characteristic signature of a companion interaction with the stellar wind. For the symbiotic star R Aqr, PACS revealed two perfectly opposing arms that in part reflect the previously observed ring-shaped nebula in the optical. However, from the far-IR there is evidence that the emitting region is elliptical rather than circular. The outline of the wind of W Aql seems to follow a large Archimedean spiral formed by the orbit of the companion but also shows strong indications of an interaction with the interstellar medium. We investigated the nature of the companion of W Aql and found that the magnitude of the orbital period supports the size of the spiral outline. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

  20. Cosmogenic nuclides in cometary materials: Implications for rate of mass loss and exposure history

    NASA Technical Reports Server (NTRS)

    Herzog, G. F.; Englert, P. A. J.; Reedy, R. C.

    1989-01-01

    As planned, the Rosetta mission will return to earth with a 10-kg core and a 1-kg surface sample from a comet. The selection of a comet with low current activity will maximize the chance of obtaining material altered as little as possible. Current temperature and level of activity, however, may not reliably indicate previous values. Fortunately, from measurements of the cosmogenic nuclide contents of cometary material, one may estimate a rate of mass loss in the past and perhaps learn something about the exposure history of the comet. Perhaps the simplest way to estimate the rate of mass loss is to compare the total inventories of several long-lived cosmogenic radionuclides with the values expected on the basis of model calculations. Although model calculations have become steadily more reliable, application to bodies with the composition of comets will require some extension beyond the normal range of use. In particular, the influence of light elements on the secondary particle cascade will need study, in part through laboratory irradiations of volatile-rich materials. In the analysis of cometary data, it would be valuable to test calculations against measurements of short-lived isotopes.

  1. Stringent X-Ray Constraints on Mass Loss from Proxima Centauri

    NASA Astrophysics Data System (ADS)

    Wargelin, Bradford J.; Drake, Jeremy J.

    2002-10-01

    We have analyzed data from two Chandra imaging observations of Proxima Centauri, searching for an X-ray halo arising from charge exchange between highly charged ions in its stellar wind and neutral gas in the surrounding interstellar medium. Based upon our model of Proxima Cen's charge exchange emission, the absence of any detectable charge exchange signal places a statistical 3 σ upper limit of ~3×10-13 Msolar yr-1 (14 Msolar) on the mass-loss rate (9 Msolar for the 2 σ limit and 4 Msolar for 1 σ), with a model uncertainty of roughly a factor of 3. This is orders of magnitude smaller than the upper limits that have been placed on late-type dwarf stars using radio observations, and it supports a recent mass-loss result for Proxima Cen based on Lyα absorption profiles. We have also studied the coronal spectrum, both in quiescence and during a prominent flare. Results are consistent with those obtained in previous X-ray observations, but a firm determination of coronal metal abundances remains elusive.

  2. Molecular formation along the atmospheric mass loss of HD 209458b and similar Hot Jupiters

    NASA Astrophysics Data System (ADS)

    Pinotti, R.; Boechat-Roberty, H. M.

    2016-02-01

    The chemistry along the mass loss of Hot Jupiters is generally considered to be simple, consisting mainly of atoms, prevented from forming more complex species by the intense radiation field from their host stars. In order to probe the region where the temperature is low (T<2000 K), we developed a 1D chemical and photochemical reaction model of the atmospheric mass loss of HD 209458b, involving 56 species, including carbon chain and oxygen-bearing ones, interacting through 566 reactions. The simulation results indicate that simple molecules like OH+, H2O+ and H3O+ are formed inside the region, considering that residual H2 survives in the exosphere, a possibility indicated by recent observational work. The molecules are formed and destroyed within a radial distance of less than 107 km, but the estimated integrated column density of OH+, a potential tracer of H2, is high enough to allow detection, which, once achieved, would indicate a revision of chemical models of the upper atmosphere of Hot Jupiters. For low density Hot Jupiters receiving less intense XUV radiation from their host stars than HD 209458b, molecular species could conceivably be formed with a higher total column density.

  3. Loss of 45 Da from a2 Ions and Preferential Loss of 48 Da from a2 Ions Containing Methionine in Peptide Ion Tandem Mass Spectra

    NASA Astrophysics Data System (ADS)

    Simón-Manso, Yamil; Neta, Pedatsur; Yang, Xiaoyu; Stein, Stephen E.

    2011-02-01

    While analyzing tandem mass spectra of tryptic tripeptides, intense unassigned peaks were observed, corresponding to neutral loss of 45 Da from a2 ions. This process was confirmed by MS3 experiments. Based on exact mass analysis, the loss was ascribed to (NH3 + CO) or formamide. The proposed mechanism involves a cyclic form of the a2 ions. The structure of the a2 - 45 ions was confirmed by their fragmentation in MS3 experiments. Loss of (NH3 + CO) from the a2 ions occurs in competition with other paths, such as the loss of H2O or the formation of immonium ions. However, if the a2 ion contains methionine, a neutral loss of 48 Da (ascribed to CH3SH) predominates, and is followed by the loss of (NH3 + CO). These processes were confirmed by MS3 experiments. The intensity of the a2 - 48 peak formed from XaaMet has a maximum value of 42% (of the total intensity of all ions) for Xaa=Gly, varies between 15% and 40% for most other Xaa residues, is lower for residues that can undergo loss of water or ammonia, and is very low for Lys or Arg. When the order of the residues is reversed to MetXaa, the loss of 48 Da is much smaller. This effect can be used to determine the sequence of b2 ions containing Met in proteomic studies. Considerable loss of CH3SH is observed from doubly protonated tryptic tripeptides with N-terminal Met, but the loss is much less when they are singly protonated or when Met is in the center position.

  4. The Roles of Tidal Evolution and Evaporative Mass Loss in the Origin of CoRoT-7 b

    NASA Technical Reports Server (NTRS)

    Jackson, Brian; Miller, Neil; Barnes, Rory; Raymond, Sean N.; Fortney, Jonathan J.; Greenberg, Richard

    2010-01-01

    CoRoT-7 b is the first confirmed rocky exoplanet, but, with an orbital semimajor axis of 0.0172 au, its origins may be unlike any rocky planet in our Solar System. In this study, we consider the roles of tidal evolution and evaporative mass loss in CoRoT-7 b's history, which together have modified the planet's mass and orbit. If CoRoT-7 b has always been a rocky body, evaporation may have driven off almost half its original mass, but the mass loss may depend sensitively on the extent of tidal decay of its orbit. As tides caused CoRoT-7 b's orbit to decay, they brought the planet closer to its host star, thereby enhancing the mass loss rate. Such a large mass loss also suggests the possibility that CoRoT-7 b began as a gas giant planet and had its original atmosphere completely evaporated. In this case, we find that CoRoT-7 b's original mass probably did not exceed 200 Earth masses (about two-third of a Jupiter mass). Tides raised on the host star by the planet may have significantly reduced the orbital semimajor axis, perhaps causing the planet to migrate through mean-motion resonances with the other planet in the system, CoRoT-7 c. The coupling between tidal evolution and mass loss may be important not only for CoRoT-7 b but also for other close-in exoplanets, and future studies of mass loss and orbital evolution may provide insight into the origin and fate of close-in planets, both rocky and gaseous.

  5. Sensitivity study for s process nucleosynthesis in AGB stars

    NASA Astrophysics Data System (ADS)

    Koloczek, A.; Thomas, B.; Glorius, J.; Plag, R.; Pignatari, M.; Reifarth, R.; Ritter, C.; Schmidt, S.; Sonnabend, K.

    2016-03-01

    In this paper we present a large-scale sensitivity study of reaction rates in the main component of the s process. The aim of this study is to identify all rates, which have a global effect on the s process abundance distribution and the three most important rates for the production of each isotope. We have performed a sensitivity study on the radiative 13C-pocket and on the convective thermal pulse, sites of the s process in AGB stars. We identified 22 rates, which have the highest impact on the s-process abundances in AGB stars.

  6. Limits on the significant mass-loss scenario based on the globular clusters of the Fornax dwarf spheroidal galaxy

    NASA Astrophysics Data System (ADS)

    Khalaj, P.; Baumgardt, H.

    2016-03-01

    Many of the scenarios proposed to explain the origin of chemically peculiar stars in globular clusters (GCs) require significant mass loss (≥95 per cent) to explain the observed fraction of such stars. In the GCs of the Fornax dwarf galaxy, significant mass loss could be a problem. Larsen et al. showed that there is a large ratio of GCs to metal-poor field stars in Fornax and about 20-25 per cent of all the stars with [Fe/H] < -2 belong to the four metal-poor GCs. This imposes an upper limit of ˜80 per cent mass loss that could have happened in Fornax GCs. In this paper, we propose a solution to this problem by suggesting that stars can leave the Fornax galaxy. We use a series of N-body simulations to determine the limit of mass loss from Fornax as a function of the initial orbital radii of GCs and the speed with which stars leave Fornax GCs. We consider a set of cored and cuspy density profiles for Fornax. Our results show that with a cuspy model for Fornax, the fraction of stars that leave the galaxy can be as high as ˜90 per cent, when the initial orbital radii of GCs are R = 2-3 kpc and the initial speed of stars is v > 20 km s-1. We show that such large velocities can be achieved by mass loss induced by gas expulsion but not mass loss induced by stellar evolution. Our results imply that one cannot interpret the metallicity distribution of Fornax field stars as evidence against significant mass loss in Fornax GCs, if mass loss is due to gas expulsion.

  7. Predictions for Dusty Mass Loss from Asteroids During Close Encounters with Solar Probe Plus

    NASA Astrophysics Data System (ADS)

    Cranmer, Steven R.

    2016-06-01

    The Solar Probe Plus (SPP) mission will explore the Sun's corona and innermost solar wind starting in 2018. The spacecraft will also come close to a number of Mercury-crossing asteroids with perihelia less than 0.3 AU. At small heliocentric distances, these objects may begin to lose mass, thus becoming "active asteroids" with comet-like comae or tails. This paper assembles a database of 97 known Mercury-crossing asteroids that may be encountered by SPP, and it presents estimates of their time-dependent visible-light fluxes and mass loss rates. Assuming a similar efficiency of sky background subtraction as was achieved by STEREO , we find that approximately 80 % of these asteroids are bright enough to be observed by the Wide-field Imager for SPP (WISPR). A model of gas/dust mass loss from these asteroids is developed and calibrated against existing observations. This model is used to estimate the visible-light fluxes and spatial extents of spherical comae. Observable dust clouds occur only when the asteroids approach the Sun closer than 0.2 AU. The model predicts that during the primary SPP mission between 2018 and 2025, there should be 113 discrete events (for 24 unique asteroids) during which the modeled comae have angular sizes resolvable by WISPR. The largest of these correspond to asteroids 3200 Phaethon, 137924, 155140, and 289227, all with angular sizes of roughly 15-30 arcminutes. We note that the SPP trajectory may still change, but no matter the details there should still be multiple opportunities for fruitful asteroid observations.

  8. Acceleration of the Greenland ice sheet mass loss as observed by GRACE: Confidence and sensitivity

    NASA Astrophysics Data System (ADS)

    Svendsen, P. L.; Andersen, O. B.; Nielsen, A. A.

    2013-02-01

    We examine the scale and spatial distribution of the mass change acceleration in Greenland and its statistical significance, using processed gravimetric data from the GRACE mission for the period 2002-2011. Three different data products - the CNES/GRGS, DMT-1b and GGFC GRACE solutions - have been used, all revealing an accelerating mass loss in Greenland, though with significant local differences between the three datasets. Compensating for leakage effects, we obtain acceleration values of -18.6 Gt/yr2 for CNES/GRGS, -8.8 Gt/yr2 for DMT-1b, and -14.8 Gt/yr2 for GGFC. We find considerable mass loss acceleration in the Canadian Arctic Archipelago, some of which will leak into the values for Greenland, depending on the approach used, and for our computations the leakage has been estimated at up to -4.7 Gt/yr2. The length of the time series of the GRACE data makes a huge difference in establishing an acceleration of the data. For both 10-day and monthly GRACE solutions, an observed acceleration on the order of 10-20 Gt/yr2 is shown to require more than 5 yrs of data to establish with statistical significance. In order to provide an independent evaluation, ICESat laser altimetry data have been smoothed to match the resolution of the GRACE solutions. This gives us an estimated upper bound for the acceleration of about -29.7 Gt/yr2 for the period 2003-2009, consistent with the acceleration values and corresponding confidence intervals found with GRACE data.

  9. Resistance training and timed amino acid supplementation protects against the loss of muscle mass and strength with disuse

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Space flight and ground-based models of weightlessness result in loss of muscle mass and strength. Amino acid supplementation and resistance training reverse these losses but their optimal combination is not known. We examined the effect of an amino acid supplement and resistance training on muscl...

  10. Ice flow dynamics and mass loss of Totten Glacier, East Antarctica, from 1989 to 2015

    NASA Astrophysics Data System (ADS)

    Li, Xin; Rignot, Eric; Mouginot, Jeremie; Scheuchl, Bernd

    2016-06-01

    Totten Glacier has the largest ice discharge in East Antarctica and a basin grounded mostly below sea level. Satellite altimetry data have revealed ice thinning in areas of fast flow. Here we present a time series of ice velocity measurements spanning from 1989 to 2015 using Landsat and interferometric synthetic-aperture radar data, combined with ice thickness from Operation IceBridge, and surface mass balance from Regional Atmospheric Climate Model. We find that the glacier speed exceeded its balance speed in 1989-1996, slowed down by 11 ± 12% in 2000 to bring its ice flux in balance with accumulation (65 ± 4 Gt/yr), then accelerated by 18 ± 3% until 2007, and remained constant thereafter. The average ice mass loss (7 ± 2 Gt/yr) is dominated by ice dynamics (73%). Its acceleration (0.6 ± 0.3 Gt/yr2) is dominated by surface mass balance (80%). Ice velocity apparently increased when ocean temperature was warmer, which suggests a linkage between ice dynamics and ocean temperature.

  11. Vertical distribution of dry mass in cereals straw and its loss during harvesting

    NASA Astrophysics Data System (ADS)

    Zajaç, T.; Oleksy, A.; Stokłosa, A.; Klimek-Kopyra, A.; Macuda, J.

    2013-01-01

    The study aimed at evaluating the distribution of mass in the straw of cereal species and also at assessing the straw yield and its losses resulting from the amount of the stubble left in the field. It was found empirically that the wheat culms are composed of five internodes, and in barley, triticale and oats of six. The highest straw mass per 1 cm was found in the second internode in both forms of wheat and winter triticale, whereas barley and oats gathered the highest weight in the first internode. In the southern part of Silesia species and forms of cereals differed in the straw yield, which can be arranged as follows, from the highest: winter wheat > spring wheat, winter triticale, winter barley, and oats > spring barley. Due to the specific distribution of dry matter in each of internodes of both wheat forms - winter and spring, they loose less stubble mass (22 and 24%, respectively), comparing to other cereals, especially spring barley, which loose 31% yield of straw in the stubble of 15 cm height.

  12. Theoretical studies of mass loss and shock phenomena in cool star envelopes

    NASA Technical Reports Server (NTRS)

    Hartmann, Lee

    1988-01-01

    To show the difficulty of producing the blue-shifted emission of (O I) and (S II) from T Tauri stars directly in the stellar wind, an element of gas in a radially expanding stellar wind was followed as it cooled and recombined. Results indicate that T Tauri winds must be heated at large distances from the star to produce the (S II) emission. A shock between the wind and the disk is an attractive mechanism to produce this heating. When the theory is applied to a simple disk model, a number of predictions and implications are evident, for example, that some T Tauri stars eject mass near the equatorial plane. In a second study, spectral energy distributions of T Tauri stars were analyzed to place limits on the amount of accretion which might occur during the early phase of stellar evolution. The best match to H-alpha line profiles is for models in which the turbulent velocity dominates close to the star, while expansion dominates farther out. Such a model predicts, for instance, that a mass loss rate of 1/10,000,000 solar masses per year is required to account for the blue-shifted Na I absorption of some objects.

  13. A turbulent wake as a tracer of 30,000 years of Mira's mass loss history.

    PubMed

    Martin, D Christopher; Seibert, Mark; Neill, James D; Schiminovich, David; Forster, Karl; Rich, R Michael; Welsh, Barry Y; Madore, Barry F; Wheatley, Jonathan M; Morrissey, Patrick; Barlow, Tom A

    2007-08-16

    Mira is one of the first variable stars ever discovered and it is the prototype (and also the nearest example) of a class of low-to-intermediate-mass stars in the late stages of stellar evolution. These stars are relatively common and they return a large fraction of their original mass to the interstellar medium (ISM) (ref. 2) through a processed, dusty, molecular wind. Thus stars in Mira's stage of evolution have a direct impact on subsequent star and planet formation in their host galaxy. Previously, the only direct observation of the interaction between Mira-type stellar winds and the ISM was in the infrared. Here we report the discovery of an ultraviolet-emitting bow shock and turbulent wake extending over 2 degrees on the sky, arising from Mira's large space velocity and the interaction between its wind and the ISM. The wake is visible only in the far ultraviolet and is consistent with an unusual emission mechanism whereby molecular hydrogen is excited by turbulent mixing of cool molecular gas and shock-heated gas. This wind wake is a tracer of the past 30,000 years of Mira's mass-loss history and provides an excellent laboratory for studying turbulent stellar wind-ISM interactions. PMID:17700694

  14. Do Globular Clusters Care about AGB Stars? Metallicity Distribution of AGB and RGB Stars in NGC 2808

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Primas, F.; Charbonnel, C.

    2015-08-01

    Galactic globular clusters are known to have multiple stellar populations with different scenarios being debated for their origin. In this context, the core of our project is to disentangle the first and second generation stars based on their chemical properties, in order to test different model predictions. Here we present a preliminary chemical analysis of a new sample of AGB stars in NGC 2808 observed at the VLT with FLAMES, in order to further investigate the recent finding that no Na-rich stars are found on the AGB.

  15. Age Dating Merger Events in Early Type Galaxies via the Detection of AGB Light

    NASA Technical Reports Server (NTRS)

    Bothun, G.

    2005-01-01

    A thorough statistical analysis of the J-H vs. H-K color plane of all detected early type galaxies in the 2MASS catalog with velocities less than 5000 km/s has been performed. This all sky survey is not sensitive to one particular galactic environment and therefore a representative range of early type galaxy environments have been sampled. Virtually all N-body simulation so major mergers produces a central starburst due to rapid collection of gas. This central starburst is of sufficient amplitude to change the stellar population in the central regions of the galaxy. Intermediate age populations are given away by the presence of AGB stars which will drive the central colors redder in H-K relative to the J- H baseline. This color anomaly has a lifetime of 2-5 billion years depending on the amplitude of the initial starburst Employing this technique on the entire 2MASS sample (several hundred galaxies) reveals that the AGB signature occurs less than 1% of the time. This is a straightforward indication that virtually all nearby early type galaxies have not had a major merger occur within the last few billion years.

  16. The importance of Titan's current mass loss processes to understanding the evolution of Titan's atmosphere

    NASA Astrophysics Data System (ADS)

    Mandt, Kathleen; Waite, J. Hunter, Jr.; Bell, Jared; Mousis, Olivier

    2010-04-01

    Current isotopic ratios in planetary atmospheres have played an important role in determining how that atmosphere has evolved over geologic time scales (e.g. Donahue et al. 1997, Lunine et al. 1999). The current 12C/13C ratio in methane is a particularly useful indicator of Titan's atmospheric evolutionary history (Mandt et al. 2009). Primordial 12C/13C ratios throughout the solar system are limited to 89.01+4.45-2.67. (Alexander et al. 2007, Martins et al. 2008), while the methane 12C/13C ratio measured by GCMS and CIRS are 82.3+/-1.0 and 76.6+/-2.7 respectively (Niemann et al. 2005, Nixon et al. 2008). This is well below the primordial range, suggesting fractionation of the isotopes by atmospheric processes. A number of atmospheric mass loss processes can fractionate the isotopes over geologic time scales. Photochemistry and escape are of particular importance (Donahue et al 1997, Mandt et al. 2009). Measurements of the 12C/13C ratios in C2 hydrocarbons show evidence of fractionation due to photochemistry (Nixon et al. 2008) that is most likely due to a kinetic isotope effect (KIE). A KIE is a mildly efficient fractionating process in which reactions involving 12C occur 1.04 times faster than reactions involving 13C. A moderate time scale, on the order of 50 to 400 million years, is required to change the 12C/13C ratio of the atmospheric methane inventory. The exact length of this time scale depends directly on the methane photochemical loss rate. Titan's photochemistry is extremely complex, and although the total photochemical loss rate is photon-limited (Lorenz et al. 1997), the literature provides a range of loss rates between 4.9 x 10^9 cm-2s-1 (Wilson and Atreya 2004) and 3.4 x 10^10 cm-2s-1 (Lebonnois et al. 2003). This range can alter the time scale for fractionation in the carbon isotopes by as much as a factor of 8. INMS measurements of the methane 12C/13C ratio in the upper atmosphere show that atmospheric escape is a more efficient fractionating

  17. Mass loss from evolved massive stars: self-consistent modeling of the wind and photosphere

    NASA Astrophysics Data System (ADS)

    Groh, J. H.

    2007-03-01

    This work analyzes the mass loss phenomenon in evolved massive stars through self-consistent modeling of the wind and photosphere of such stars, using the radiative transfer code CMFGEN. In the first part, fundamental physical parameters of Wolf-Rayet stars of spectral types WN3-w (WR 46 e WR 152) and WN6-s (WR 136) were obtained. The results clearly indicate that hydrogen is present on the surface of those stars in a considerable fraction, defying current evolutionary models. For both WN subtypes, significant difference between the physical parameters obtained here and in previous works were noticed. The 20-year evolution of the luminous blue variable (LBV) AG Carinae was analyzed in detail in the second part of this work. The results indicate unexpected changes in the current paradigm of massive star evolution during the S Dor cycle. In this work, the high rotational velocity obtained during the hot phases, and the transition between the bistability regimes of line-driven winds were detected for the first time in LBVs. Those results need to be considered in future analysis of such massive stars. This Thesis also presents a pioneering study about the impact of the time variability effects on the analysis of the winds of LBVs. The results achieved here are valid for the whole LBV class, and show that the mass-loss rates derived from Hα and radio free-free emission are affected by time-dependent effects. The mass-loss rate evolution during the S Dor cycle, derived using time-dependent models, implies that LBV eruptions begin well before the maximum in the visual lightcurve during this phase. The analysis of the full S Dor cycle of AG Car rule out that the S Dor variability is caused exclusively by an expanding pseudo-photosphere. The AG Car hydrostatic radius was found to vary by a factor of six between cool and hot phases, while the bolometric luminosity is 50% higher during the hot phase. Both results provide observational contraints for the physical mechanism

  18. Processes of mass loss on a debris covered glacier determined by high resolution DEM differencing

    NASA Astrophysics Data System (ADS)

    Thompson, Sarah; Benn, Doug I.; Mertes, Jordan

    2015-04-01

    In recent years the response of debris-covered glaciers to climatic warming has seen significant disscussion. The insulating properties of a debris layer (> 5-6 cm) are well established however, in the Himalayas regionally averaged thinning rates, based on satellite laser altimetry, were found to be very similar on both debris-covered, and clean ice glaciers in the Himalayas. Overall mass loss rates on large debris covered glaciers have been discussed in conjunction with supraglacial lake development and growth but the processes involved in downwasting are often numerous and complex. Here we report on mass loss measurements, from a combination of in situ lake surveys and remote sensing, on large debris covered glacier in the Khumbu Himal Nepal. Lake bathymetry sonar surveys were conducted in the winter of 2009 and 2012, and GeoEye-1 stereo imagery was acquired in 2010 and 2012. The temporal data sets were combined and differencd to allow detailed investigation of glacial surface change over the 2 year period. Ngozumpa Glacier has a stagnant ice tongue extending down to ~4650 m asl, the lower 15 km of which is debris covered. This debris covered region is highly irregular with many hollows occupied by studded with numerous supraglacial ponds and lakes. In the early 1990s a base level lake was identified ~1 km from the glacier terminus. Our results show a highly complex pattern of glacial downwasting and lake change. Numerous examples of rapid supra glacial growth and drainage are evident, including the formation and enlargement of lakes along preexisting structures such as relic englacial drainage conduits. However, also in evidence are areas of significant lake shrinkage due to sedimentation and lake shore debris collapse. In addition to lake induced mass loss a background downwasting rate of ~ 0.5 m a-1 is evident in the lower ablation area where debris thicknesses are known to be between 1-3 m thick. The results illustrate the highly complex nature of debris

  19. Re-estimation of glacier mass loss in Greenland from GRACE with correction of land-ocean leakage effects

    NASA Astrophysics Data System (ADS)

    Jin, Shuanggen; Zou, Fang

    2015-12-01

    The Gravity Recovery and Climate Experiment (GRACE) satellites can estimate the high-precision time-varying gravity field and the changes of Earth's surface mass, which have been widely used in water cycle and glacier mass balance. However, one of larger errors in GRACE measurements, land-ocean leakage effects, restricts high precision retrieval of ocean mass and terrestrial water storage variations along the coasts, particularly estimation of mass loss in Greenland. The land-ocean leakage effect along the coasts in Greenland will contaminate the mass loss signals with significant signal attenuation. In this paper, the precise glacier mass loss in Greenland from GRACE is re-estimated with correction of land-ocean leakage effects using the forward gravity modeling. The loss of Greenland ice-sheets is - 102.8 ± 9.01 Gt/a without removing leakage effect, but - 183.0 ± 19.91 Gt/a after removing the leakage effect from September 2003 to March 2008, which has a good agreement with ICESat results of - 184.8 ± 28.2 Gt/a. From January 2003 to December 2013, the total Greenland ice-sheet loss is at - 261.54 ± 6.12 Gt/a from GRACE measurements with removing the leakage effect by 42.4%, while two-thirds of total glacier melting in Greenland occurred in southern Greenland in the past 11 years. The secular leakage effects on glacier melting estimate is mainly located in the coastal areas, where larger glacier signals are significantly attenuated due to leaking out into the ocean. Furthermore, the leakage signals also have remarkable effects on seasonal and acceleration variations of glacier mass loss in Greenland. More significantly accelerated loss of glacier mass in Greenland is found at - 26.19 Gt/a2 after correcting for leakage effects.

  20. Setting the stage for circumstellar interaction in core-collapse supernovae. II. Wave-driven mass loss in supernova progenitors

    SciTech Connect

    Shiode, Joshua H.; Quataert, Eliot E-mail: eliot@berkeley.edu

    2014-01-01

    Supernovae (SNe) powered by interaction with circumstellar material provide evidence for intense stellar mass loss during the final years before core collapse. We have argued that during and after core neon burning, internal gravity waves excited by core convection can tap into the core fusion power and transport a super-Eddington energy flux out to the stellar envelope, potentially unbinding ∼1 solar mass of material. In this work, we explore the internal conditions of SN progenitors using the MESA one-dimensional stellar evolution code in search of those most susceptible to wave-driven mass loss. We focus on simple, order of magnitude considerations applicable to a wide range of progenitors. Wave-driven mass loss during core neon and oxygen fusion happens preferentially in either lower mass (∼20 solar mass zero-age main sequence) stars or massive, sub-solar metallicity stars. Roughly 20% of the SN progenitors we survey can excite 10{sup 46-48} erg of energy in waves that can potentially drive mass loss within a few months to a decade of core collapse. This energy can generate circumstellar environments with 10{sup –3}-1 solar masses reaching 100 AU before explosion. We predict a correlation between the energy associated with pre-SN mass ejection and the time to core collapse, with the most intense mass loss preferentially occurring closer to core collapse. During silicon burning, wave energy may inflate 10{sup –3}-1 solar masses of the envelope to 10-100 s of solar radii. This suggests that some nominally compact SN progenitors (Type Ibc progenitors) will have a significantly different SN shock breakout signature than traditionally assumed.

  1. Setting the Stage for Circumstellar Interaction in Core-Collapse Supernovae. II. Wave-driven Mass Loss in Supernova Progenitors

    NASA Astrophysics Data System (ADS)

    Shiode, Joshua H.; Quataert, Eliot

    2014-01-01

    Supernovae (SNe) powered by interaction with circumstellar material provide evidence for intense stellar mass loss during the final years before core collapse. We have argued that during and after core neon burning, internal gravity waves excited by core convection can tap into the core fusion power and transport a super-Eddington energy flux out to the stellar envelope, potentially unbinding ~1 solar mass of material. In this work, we explore the internal conditions of SN progenitors using the MESA one-dimensional stellar evolution code in search of those most susceptible to wave-driven mass loss. We focus on simple, order of magnitude considerations applicable to a wide range of progenitors. Wave-driven mass loss during core neon and oxygen fusion happens preferentially in either lower mass (~20 solar mass zero-age main sequence) stars or massive, sub-solar metallicity stars. Roughly 20% of the SN progenitors we survey can excite 1046-48 erg of energy in waves that can potentially drive mass loss within a few months to a decade of core collapse. This energy can generate circumstellar environments with 10-3-1 solar masses reaching 100 AU before explosion. We predict a correlation between the energy associated with pre-SN mass ejection and the time to core collapse, with the most intense mass loss preferentially occurring closer to core collapse. During silicon burning, wave energy may inflate 10-3-1 solar masses of the envelope to 10-100 s of solar radii. This suggests that some nominally compact SN progenitors (Type Ibc progenitors) will have a significantly different SN shock breakout signature than traditionally assumed.

  2. Clinical and hormonal variables related to bone mass loss in anorexia nervosa patients.

    PubMed

    Fernández-Soto, María Luisa; González-Jiménez, Amalia; Chamorro-Fernández, Marta; Leyva-Martínez, Socorro

    2013-01-01

    A better understanding of the prognostic factors of low bone mass in anorexia nervosa (AN) and development of effective therapeutic strategies is critical. In order to determine which clinical, biochemical, and/or hormonal parameters could be related to bone mineral density (BMD), 47 female AN patients were classified according to the WHO osteoporosis criteria at lumbar spine (LS). This was a cross-sectional study of 16 AN women with osteoporosis criteria and 31without. Control group was 25 healthy, normal-weight, age-matched women. We assessed BMD using dual-energy X-ray absorptiometry at the LS and body composition. We measured serum fasting cortisol, estradiol, insulin-like growth factor-1 (IGF-1), leptin, sex hormone-binding globulin, albumin and retinol binding protein levels. The prevalence of osteoporosis was 34% and osteopenia 19% at the LS. The AN group with osteoporosis had lower IGF-1 and estradiol levels (both p<0.001), lower serum leptin (p<0.02), and higher cortisolemia (p<0.03) levels compared with AN group without osteoporosis. The BMD and T-score at LS was inversely related to the duration of amenorrhea (p<0.02) and directly related to body mass index (BMI, p<0.002), total fat mass (p<0.03), serum IGF-1 (p<0.01), and estradiol levels (p<0.001) in AN patients. We conclude that AN women with a significant BMD loss have a high risk of developing osteoporosis. A low BMD is a consequence of hormonal alterations which include hypoestrogenism, hypoleptinemia, hypercortisolism, and decreases in IGF-1 levels, as well as a low BMI and fat mass. PMID:23601428

  3. Variability and mass loss in IA O-B-A supergiants

    NASA Technical Reports Server (NTRS)

    Schild, R. E.; Garrison, R. F.; Hiltner, W. A.

    1983-01-01

    Recently completed catalogs of MK spectral types and UBV photometry of 1227 OB stars in the southern Milky Way have been analyzed to investigate brightness and color variability among the Ia supergiants. It is found that brightness variability is common among the O9-B1 supergiants with typical amplitudes about 0.1 and time scales longer than a week and shorter than 1000 days. Among the A supergiants fluctuations in U-B color are found on similar time scales and with amplitude about 0.1. For many early Ia supergiants there is a poor correlation between Balmer jump and spectral type, as had been known previously. An attempt to correlate the Balmer jump deficiency with mass loss rate yielded uncertain results.

  4. Probing Ancient Mass Loss with AKARI's Extended Thermal Dust Emission Objects

    NASA Astrophysics Data System (ADS)

    Tomasino, Rachael L.; Ueta, Toshiya; Yamamura, Issei; Izumiura, Hideyuki

    We present the method for the calibration and analysis of 166 far-IR extended thermal dust emission objects that were observed with AKARI’s FIS detector. The primary goal of the analysis of this data set is to map the circumstellar shells of evolved stars in detail to understand the ancient history of dusty mass loss. After establishing an extended aperture photometry method, we re-characterize the flux dependent slow transient response correction factors for each of the four wavelength bands and propose a new flux calibration method for extended sources. Using these new correction factors, the photometric measurements are made using a extended aperture which is defined by a background + 3σ threshold. With photometry measurements for each of the four FIS bands, an SED of a modified blackbody was fit to produce the emissivity beta, effective temperature, and color correction factor.

  5. Brief Communication: Global glacier mass loss reconstructions during the 20th century are consistent

    NASA Astrophysics Data System (ADS)

    Marzeion, B.; Leclercq, P. W.; Cogley, J. G.; Jarosch, A. H.

    2015-07-01

    Estimates of the contribution of glaciers to sea-level rise during the 20th century that were published in recent years are strongly divergent. Advances in data availability have allowed revisions of some of these published estimates. Here we show that outside of Antarctica, the global estimates of glacier mass loss obtained from glacier-length-based reconstructions and from a glacier model driven by gridded climate observations are now consistent with each other, and also with an estimate for the years 2003-2009 that is mostly based on remotely sensed data. This consistency is found throughout the entire common periods of the respective data sets. Inconsistencies of reconstructions and observations persist in estimates on regional scales.

  6. Glacier mass loss. Dynamic thinning of glaciers on the Southern Antarctic Peninsula.

    PubMed

    Wouters, B; Martin-Español, A; Helm, V; Flament, T; van Wessem, J M; Ligtenberg, S R M; van den Broeke, M R; Bamber, J L

    2015-05-22

    Growing evidence has demonstrated the importance of ice shelf buttressing on the inland grounded ice, especially if it is resting on bedrock below sea level. Much of the Southern Antarctic Peninsula satisfies this condition and also possesses a bed slope that deepens inland. Such ice sheet geometry is potentially unstable. We use satellite altimetry and gravity observations to show that a major portion of the region has, since 2009, destabilized. Ice mass loss of the marine-terminating glaciers has rapidly accelerated from close to balance in the 2000s to a sustained rate of -56 ± 8 gigatons per year, constituting a major fraction of Antarctica's contribution to rising sea level. The widespread, simultaneous nature of the acceleration, in the absence of a persistent atmospheric forcing, points to an oceanic driving mechanism. PMID:25999505

  7. Peculiar Transients as Probes of Stellar Evolution and Mass-Loss

    NASA Astrophysics Data System (ADS)

    Drout, Maria; Berger, Edo; Pan-STARRS1 CFA/JHU Transient Team

    2016-01-01

    Multi-wavelength observations of supernovae not only probe the explosion mechanism, but also carry information about the configuration of the star at the moment of collapse and the mass-loss history of the progenitor system in the years immediately preceding its death. The study of supernovae therefore offers us one of our only observational views of the final stages of stellar evolution. As a result, the discovery by wide-field dedicated surveys of new classes of astronomical transients at an ever-increasing rate has both expanded the types of stellar systems that we can directly probe and challenged some of our existing views of how these uncertain final stages proceed. In this talk I will discuss my thesis work on several types of new and peculiar astronomical transients and what their properties, intrinsic rates, and explosion environments are teaching us about stellar evolution and stellar death.

  8. Spectroscopic and photometric monitoring of southern post-AGB stars

    NASA Astrophysics Data System (ADS)

    Pooley, D. J.; Cottrell, P. L.; Pollard, K. R.; Albrow, M. D.

    2004-05-01

    We present the results of contemporaneous photometric and spectroscopic monitoring of 20 post-AGB stars from Mt John University Observatory. Photometric measures were carried our suing Johnson BV and Cousins RI filters, and the radial velocity measurements were acquired using spectra from an echelle spectrograph. Our program spanned five years and the stars covered a range of spectral types from B to K in order to investigate the behavior of post-AGB stars as they evolve away from the AGB. A number of stars proved to be variable inways incompatible with post-AGB models and are reclassified. Periodicities are presented for a number of stars. Photometrically, HD 70379 was found to be pulsating in two modes with periods of 85 and 97 d. The radial velocities also varied, with the peak amplitude occurring when the photometry was also changing most. AI CMi presented three different types of spectra associated with photometric brightness, with varying strengths of narrow emission lines and molecular bandheads. The Hα profiles in almost all of the stars show evidence of emission which varies on time scales of days to months. The Na D line profiles are generally complex showing between 4 and 7 components due to both circumstellar and interstellar material.

  9. The Governance Committee: Independent Institutions. AGB Effective Committee Series

    ERIC Educational Resources Information Center

    Wilson, E. B.; Lanier, James L.

    2013-01-01

    This publication is part of an AGB series devoted to strengthening the role of key standing committees of governing boards. While there is no optimal committee system for institutions of higher education, certain principles, practices, and procedures prevail. The best practices outlined in this publication support the objectives of board…

  10. Mass-loss rates of "hot-Jupiter" exoplanets with various types of gaseous envelopes

    NASA Astrophysics Data System (ADS)

    Cherenkov, A. A.; Bisikalo, D. V.; Kaigorodov, P. V.

    2014-10-01

    According to the compuations results obtained by Bisikalo et al. (2013) for the gas-dynamical effect of stellar winds on exoplanet atmospheres, three types of gaseous envelopes can form around hot Jupiters: closed, quasi-closed, and open. The type of envelope that forms depends on the position of the frontal collision point (where the dynamical pressure of the wind is equal to the pressure of the surrounding atmosphere) relative to the Roche-lobe boundaries. Closed envelopes are formed around planets whose atmospheres lie completely within their Roche lobes. If the frontal collision point is located outside the Roche lobe, the atmospheric material begins to flow out through the Lagrangian points L1 and L2, which can result in the formation of quasi-closed (if the dynamical pressure of the stellar wind stops the outflow through L1) or open gaseous envelopes. The example of the typical hot Jupiter HD 209458b is considered for four sets of atmospheric parameters, to determine the mass-loss rates for the different types of envelopes arising with these parameters. The mass-loss rates based on the modeling results were estimated to be Ṁ ≤ 109 g/s for a closed atmosphere, Ṁ ≃ 3 × 109 g/s for a quasi-closed atmosphere, and Ṁ ≃ 3 × 1010 g/s for an open atmosphere. The matter in the closed and quasi-closed atmospheres flows out mainly through L2, and the matter in open envelopes primarily through L1.

  11. THE CORE-CUSP PROBLEM IN COLD DARK MATTER HALOS AND SUPERNOVA FEEDBACK: EFFECTS OF MASS LOSS

    SciTech Connect

    Ogiya, Go; Mori, Masao

    2011-07-20

    The core-cusp problem remains as one of the unsolved discrepancies between observations and theories predicted by the standard paradigm of cold dark matter (CDM) cosmology. To solve this problem, we perform N-body simulations to study the nonlinear response of CDM halos to the variance of the gravitational potential induced by gas removal from galaxy centers. In this study, we focus on the timescale of the gas ejection, which is strongly correlated with stellar activities, and demonstrate that it is one of the key factors in determining the dynamical response of CDM halos. The results of simulations show that the power-law index of the mass-density profile of the dark matter (DM) halo is correlated with the timescale of the mass loss and it is flatter when the mass loss occurs over a short time than when it occurs over a long time. However, it is still larger than typical observational values; in other words, the central cusp remains in the simulations for any mass-loss model. Moreover, for the slow mass-loss case, the final density profile of the DM halo recovers the universal density profiles predicted by the CDM cosmology. Therefore, the mass loss driven by stellar feedback may not be an effective mechanism to flatten the central cusp.

  12. Radial velocity variable, hot post-AGB stars from the MUCHFUSS project. Classification, atmospheric parameters, formation scenarios

    NASA Astrophysics Data System (ADS)

    Reindl, N.; Geier, S.; Kupfer, T.; Bloemen, S.; Schaffenroth, V.; Heber, U.; Barlow, B. N.; Østensen, R. H.

    2016-03-01

    In the course of the MUCHFUSS project we recently discovered four radial velocity (RV) variable, hot (Teff≈ 80 000-110 000 K) post-asymptotic giant branch (AGB) stars. Among them, we found the first known RV variable O(He) star, the only second known RV variable PG 1159 close binary candidate, as well as the first two naked (i.e., without planetary nebula (PN)) H-rich post-AGB stars of spectral type O(H) that show significant RV variations. We present a non-LTE spectral analysis of these stars along with one further O(H)-type star whose RV variations were found to be not significant. We also report the discovery of a far-infrared excess in the case of the PG 1159 star. None of the stars in our sample displays nebular emission lines, which can be explained well in terms of a very late thermal pulse evolution in the case of the PG 1159 star. The "missing" PNe around the O(H)-type stars seems strange, since we find that several central stars of PNe have much longer post-AGB times. Besides the non-ejection of a PN, the occurrence of a late thermal pulse, or the re-accretion of the PN in the previous post-AGB evolution offer possible explanations for those stars not harbouring a PN (anymore). In the case of the O(He) star J0757, we speculate that it might have been previously part of a compact He transferring binary system. In this scenario, the mass transfer must have stopped after a certain time, leaving behind a low-mass close companion that may be responsible for the extreme RV shift of 107.0 ± 22.0 km s-1 that was measured within only 31 min.

  13. Ice sheet mass loss caused by dust and black carbon accumulation

    NASA Astrophysics Data System (ADS)

    Goelles, T.; Bøggild, C. E.; Greve, R.

    2015-09-01

    Albedo is the dominant factor governing surface melt variability in the ablation area of ice sheets and glaciers. Aerosols such as mineral dust and black carbon (soot) accumulate on the ice surface and cause a darker surface and therefore a lower albedo. The darkening effect on the ice surface is currently not included in sea level projections, and the effect is unknown. We present a model framework which includes ice dynamics, aerosol transport, aerosol accumulation and the darkening effect on ice albedo and its consequences for surface melt. The model is applied to a simplified geometry resembling the conditions of the Greenland ice sheet, and it is forced by several temperature scenarios to quantify the darkening effect of aerosols on future mass loss. The effect of aerosols depends non-linearly on the temperature rise due to the feedback between aerosol accumulation and surface melt. According to our conceptual model, accounting for black carbon and dust in future projections of ice sheet changes until the year 3000 could induce an additional volume loss of 7 %. Since we have ignored some feedback processes, the impact might be even larger.

  14. Analysis of mass loss of a coal particle during the course of burning in a flow of inert material

    SciTech Connect

    Pelka, Piotr

    2009-08-15

    This paper is an attempt to explain the role of erosion during the process of coal combustion in a circulating fluidized bed. Different kinds of carbon deposits found in Poland, both bituminous as well as lignite with the particle of 10 mm in diameter were the subject of the research. According to many publications it is well known that erosion plays a significant role in coal combustion, by changing its mechanism as well as generating an additional mass loss of the mother particle. The purpose of this research was to determine the influence of an inert material on an erosive mass loss of a single coal particle burning in a two-phase flow. The determination of the influence of a coal type, the rate of flow of inert material and the temperature inside the furnace on the erosive mass loss of burning coal particle was also taken into consideration. The results obtained indicate that the velocity of the erosive mass loss depends on the chemical composition and petrographic structure of burning coal. The mechanical interaction of inert and burning coal particles leads to the shortening of the period of overall mass loss of the coal particle by even two times. The increase in the rate of flow of the inert material intensifies the generation of mass loss by up to 100%. The drop in temperature which slows down the combustion process, decreases the mass loss of the coal particle as the result of mechanical interaction of the inert material. As was observed, the process of percolation plays a significant role by weakening the surface of the burning coal. (author)

  15. Contributions of natural and anthropogenic radiative forcing to mass loss of Northern Hemisphere mountain glaciers and quantifying their uncertainties.

    PubMed

    Hirabayashi, Yukiko; Nakano, Kazunari; Zhang, Yong; Watanabe, Satoshi; Tanoue, Masahiro; Kanae, Shinjiro

    2016-01-01

    Observational evidence indicates that a number of glaciers have lost mass in the past. Given that glaciers are highly impacted by the surrounding climate, human-influenced global warming may be partly responsible for mass loss. However, previous research studies have been limited to analyzing the past several decades, and it remains unclear whether past glacier mass losses are within the range of natural internal climate variability. Here, we apply an optimal fingerprinting technique to observed and reconstructed mass losses as well as multi-model general circulation model (GCM) simulations of mountain glacier mass to detect and attribute past glacier mass changes. An 8,800-year control simulation of glaciers enabled us to evaluate detectability. The results indicate that human-induced increases in greenhouse gases have contributed to the decreased area-weighted average masses of 85 analyzed glaciers. The effect was larger than the mass increase caused by natural forcing, although the contributions of natural and anthropogenic forcing to decreases in mass varied at the local scale. We also showed that the detection of anthropogenic or natural influences could not be fully attributed when natural internal climate variability was taken into account. PMID:27435236

  16. Contributions of natural and anthropogenic radiative forcing to mass loss of Northern Hemisphere mountain glaciers and quantifying their uncertainties

    NASA Astrophysics Data System (ADS)

    Hirabayashi, Yukiko; Nakano, Kazunari; Zhang, Yong; Watanabe, Satoshi; Tanoue, Masahiro; Kanae, Shinjiro

    2016-07-01

    Observational evidence indicates that a number of glaciers have lost mass in the past. Given that glaciers are highly impacted by the surrounding climate, human-influenced global warming may be partly responsible for mass loss. However, previous research studies have been limited to analyzing the past several decades, and it remains unclear whether past glacier mass losses are within the range of natural internal climate variability. Here, we apply an optimal fingerprinting technique to observed and reconstructed mass losses as well as multi-model general circulation model (GCM) simulations of mountain glacier mass to detect and attribute past glacier mass changes. An 8,800-year control simulation of glaciers enabled us to evaluate detectability. The results indicate that human-induced increases in greenhouse gases have contributed to the decreased area-weighted average masses of 85 analyzed glaciers. The effect was larger than the mass increase caused by natural forcing, although the contributions of natural and anthropogenic forcing to decreases in mass varied at the local scale. We also showed that the detection of anthropogenic or natural influences could not be fully attributed when natural internal climate variability was taken into account.

  17. Contributions of natural and anthropogenic radiative forcing to mass loss of Northern Hemisphere mountain glaciers and quantifying their uncertainties

    PubMed Central

    Hirabayashi, Yukiko; Nakano, Kazunari; Zhang, Yong; Watanabe, Satoshi; Tanoue, Masahiro; Kanae, Shinjiro

    2016-01-01

    Observational evidence indicates that a number of glaciers have lost mass in the past. Given that glaciers are highly impacted by the surrounding climate, human-influenced global warming may be partly responsible for mass loss. However, previous research studies have been limited to analyzing the past several decades, and it remains unclear whether past glacier mass losses are within the range of natural internal climate variability. Here, we apply an optimal fingerprinting technique to observed and reconstructed mass losses as well as multi-model general circulation model (GCM) simulations of mountain glacier mass to detect and attribute past glacier mass changes. An 8,800-year control simulation of glaciers enabled us to evaluate detectability. The results indicate that human-induced increases in greenhouse gases have contributed to the decreased area-weighted average masses of 85 analyzed glaciers. The effect was larger than the mass increase caused by natural forcing, although the contributions of natural and anthropogenic forcing to decreases in mass varied at the local scale. We also showed that the detection of anthropogenic or natural influences could not be fully attributed when natural internal climate variability was taken into account. PMID:27435236

  18. High resolution spectroscopy of the high latitude rapidly evolving post-AGB star SAO 85766 (= IRAS 18062+2410)

    NASA Astrophysics Data System (ADS)

    Parthasarathy, M.; García-Lario, P.; Sivarani, T.; Manchado, A.; Sanz Fernández de Córdoba, L.

    2000-05-01

    SAO 85766 (b = +20o) is an IRAS source with far-infrared colours similar to planetary nebulae. According to the HDE catalogue, its spectrum in 1940 was that of an A5 star. The UV fluxes and colours derived from data obtained by the TD1 satellite in 1972 also indicate that SAO 85766 was an A-type supergiant at that epoch. However, high resolution spectra of SAO 85766 obtained in 1993 in the wavelength interval 4350Ä to 8820Ä shows that now it is similar to that of an early B type post-AGB supergiant. In addition to the absorptions lines typical of a B1I type star, the spectrum of SAO 85766 is found to show numerous permitted and forbidden emission lines of several elements, typically observed in the spectra of young high density low excitation planetary nebulae. From an analysis of the absorption lines we have estimated Teff=22000+/-500 K, log g=3.0+/-0.5, xi t=15+/-2km s-1 and [M/H]=-0.6. Carbon is found to be strongly underabundant ([C/Fe] = -1.0), similarly to what has been observed in other high galactic latitude hot post-AGB stars. The underabundance of carbon and metals, high galactic latitude, high radial velocity (46 km s-1), the presence of planetary nebula type detached cold circumstellar dust shell and also the presence of low excitation nebular emission lines in the spectrum indicate that SAO 85766 is a low mass star in the post-AGB stage of evolution. The above mentioned characteristics and the variations observed in the spectrum of SAO 85766 suggest that it has rapidly evolved during the past 50 years and it is now in the early stages of the planetary nebula phase. The central star may just have become hot enough to photoionize the circumstellar envelope ejected during the previous AGB phase. >From an analysis of the nebular emission lines we find Te=10000+/- 500K and Ne=2.5 104 cm-3. The nebula also shows an abundance pattern similar to that of the central star. The rapid post-AGB evolution of SAO 85766 appears to be similar to that observed in the

  19. The origin of fluorine: abundances in AGB carbon stars revisited

    NASA Astrophysics Data System (ADS)

    Abia, C.; Cunha, K.; Cristallo, S.; de Laverny, P.

    2015-09-01

    Context. Revised spectroscopic parameters for the HF molecule and a new CN line list in the 2.3 μm region have recently become available, facilitating a revision of the F content in asymptotic giant branch (AGB) stars. Aims: AGB carbon stars are the only observationally confirmed sources of fluorine. Currently, there is no consensus on the relevance of AGB stars in its Galactic chemical evolution. The aim of this article is to better constrain the contribution of these stars with a more accurate estimate of their fluorine abundances. Methods: Using new spectroscopic tools and local thermodynamical equilibrium spectral synthesis, we redetermine fluorine abundances from several HF lines in the K-band in a sample of Galactic and extragalactic AGB carbon stars of spectral types N, J, and SC, spanning a wide range of metallicities. Results: On average, the new derived fluorine abundances are systematically lower by 0.33 dex with respect to previous determinations. This may derive from a combination of the lower excitation energies of the HF lines and the larger macroturbulence parameters used here as well as from the new adopted CN line list. Yet, theoretical nucleosynthesis models in AGB stars agree with the new fluorine determinations at solar metallicities. At low metallicities, an agreement between theory and observations can be found by handling the radiative/convective interface at the base of the convective envelope in a different way. Conclusions: New fluorine spectroscopic measurements agree with theoretical models at low and at solar metallicity. Despite this, complementary sources are needed to explain its observed abundance in the solar neighbourhood.

  20. Sauna-Induced Body Mass Loss in Young Sedentary Women and Men

    PubMed Central

    Podstawski, Robert; Boraczyński, Tomasz; Boraczyński, Michał

    2014-01-01

    The aim of the study was to evaluate the relationship between body mass index (BMI) and body mass loss (BML) induced by thermal stress in a dry sauna. The study was conducted on a group of 674 sedentary students, 326 women and 348 men aged 19-20. The correlations between BMI scores and BML were determined. The subjects were placed in supine position in a dry sauna for two sessions of 10 minutes each with a 5-minute break. The influence of BMI on the amount of BML in the sauna was determined by nonlinear stepwise regression. The smallest BML was noted in underweight subjects; students with normal weight lost more weight, whereas the greatest BML was reported in overweight and obese subjects. Persons with a high BMI are at higher risk of dehydration, and they should pay particular attention to replenishing fluids during a visit to the sauna. The proposed equations for calculating BML based on a person's BMI can be useful in estimating the amount of fluids that should be replenished by both men and women during a visit to a dry sauna. PMID:25614882

  1. Tidal heating and mass loss in neutron star binaries - Implications for gamma-ray burst models

    NASA Technical Reports Server (NTRS)

    Meszaros, P.; Rees, M. J.

    1992-01-01

    A neutron star in a close binary orbit around another neutron star (or stellar-mass black hole) spirals inward owing to gravitational radiation. We discuss the effects of tidal dissipation during this process. Tidal energy dissipated in the neutron star's core escapes mainly as neutrinos, but heating of the crust, and outward diffusion of photons, blows off the outer layers of the star. This photon-driven mass loss precedes the final coalescence. The presence of this eject material impedes the escape of gamma-rays created via neutrino interactions. If an e(+) - e(-) fireball, created in the late stages of coalescence, were loaded with (or surrounded by) material with the mean column density of the ejecta, it could not be an efficient source of gamma-rays. Models for cosmologically distant gamma-rays burst that involve neutron stars must therefore be anisotropic, so that the fireball expands preferentially in directions where the column density of previously blown-off material is far below the spherically averaged value which we have calculated. Some possible 'scenarios' along these lines are briefly discussed.

  2. On the Contribution of Clouds to Greenland Ice Sheet Mass Loss

    NASA Astrophysics Data System (ADS)

    Van Tricht, K.; Lhermitte, S.; Lenaerts, J.; Gorodetskaya, I.; L'Ecuyer, T. S.; Noel, B.; van den Broeke, M. R.; Turner, D. D.; Van Lipzig, N. P. M.

    2015-12-01

    The Greenland ice sheet (GrIS) has become one of the main contributors to global mean sea level rise, predominantly explained by a decreasing surface mass balance (SMB). Clouds are known to have a strong influence on the surface energy budget, which in consequence impacts the SMB. For example, the potentially important role of thin liquid-bearing clouds over Greenland in enhancing ice sheet melt has recently gained interest. Yet, current research is spatially and temporally limited, focusing on particular events and cloud types, while the large-scale impact of all clouds on the SMB remains unknown. Using a unique cloud product covering the entire GrIS over the period 2007-2010, consisting of active satellite remote sensing data, ground-based observations and climate model data, together with snow model simulations, we investigate the cloud radiative effect over the GrIS and the consequences for the SMB. We show a strong sensitivity of the GrIS to clouds, with a complex interplay between enhanced and reduced mass loss. We further distinguish between ice-only and liquid-bearing clouds, temporal and spatial variations in cloud impacts, and we demonstrate the large spread in simulated clouds by state-of-the-art climate models. Our results therefore urge the need for accurate cloud representations in climate models, to improve future projections of GrIS SMB and global sea level rise.

  3. Sauna-induced body mass loss in young sedentary women and men.

    PubMed

    Podstawski, Robert; Boraczyński, Tomasz; Boraczyński, Michał; Choszcz, Dariusz; Mańkowski, Stefan; Markowski, Piotr

    2014-01-01

    The aim of the study was to evaluate the relationship between body mass index (BMI) and body mass loss (BML) induced by thermal stress in a dry sauna. The study was conducted on a group of 674 sedentary students, 326 women and 348 men aged 19-20. The correlations between BMI scores and BML were determined. The subjects were placed in supine position in a dry sauna for two sessions of 10 minutes each with a 5-minute break. The influence of BMI on the amount of BML in the sauna was determined by nonlinear stepwise regression. The smallest BML was noted in underweight subjects; students with normal weight lost more weight, whereas the greatest BML was reported in overweight and obese subjects. Persons with a high BMI are at higher risk of dehydration, and they should pay particular attention to replenishing fluids during a visit to the sauna. The proposed equations for calculating BML based on a person's BMI can be useful in estimating the amount of fluids that should be replenished by both men and women during a visit to a dry sauna. PMID:25614882

  4. Nucleus and Mass Loss from Active Asteroid 313P/Gibbs

    NASA Astrophysics Data System (ADS)

    Jewitt, David; Li, Jing; Agarwal, Jessica; Weaver, Harold; Mutchler, Max; Larson, Stephen

    2015-09-01

    We present Hubble Space Telescope observations of active asteroid 313P/Gibbs (formerly P/2014 S4) taken over the five month interval from 2014 October to 2015 March. This object has been recurrently active near perihelion (at 2.4 AU) in two different orbits, a property that is naturally explained by the sublimation of near surface ice but which is difficult to reconcile with other activity mechanisms. We find that the mass loss peaks near 1 kg s-1 in October and then declines over the subsequent months by about a factor of five, at nearly constant heliocentric distance. This decrease is too large to be caused by the change in heliocentric distance during the period of observation. However, it is consistent with sublimation from an ice patch shadowed by local topography, for example in a pit like those observed on the nucleus of short-period comet 67P/Churyumov-Gerasimenko. While no unique interpretation is possible, a simple self shadowing model shows that sublimation from a pit with a depth to diameter ratio near 1/2 matches the observed rate of decline of the activity, while deeper and shallower pits do not. We estimate the nucleus radius to be 700 ± 100 m (geometric albedo 0.05 assumed). Measurements of the spatial distribution of the dust were obtained from different viewing geometries. They show that dust was ejected continuously not impulsively, that the effective particle size is large, ˜50 μm, and that the ejection speed is ˜2.5 m s-1. The total dust mass ejected is ˜107 kg, corresponding to ˜10-5 of the nucleus mass. The observations are consistent with partially shadowed sublimation from ˜104 m2 of ice, corresponding to ˜0.2% of the nucleus surface. For ice to survive in 313P for billion-year timescales requires that the duty cycle for sublimation be ≲10-3.

  5. Mid-Pleistocene climate transition drives net mass loss from rapidly uplifting St. Elias Mountains, Alaska.

    PubMed

    Gulick, Sean P S; Jaeger, John M; Mix, Alan C; Asahi, Hirofumi; Bahlburg, Heinrich; Belanger, Christina L; Berbel, Glaucia B B; Childress, Laurel; Cowan, Ellen; Drab, Laureen; Forwick, Matthias; Fukumura, Akemi; Ge, Shulan; Gupta, Shyam; Kioka, Arata; Konno, Susumu; LeVay, Leah J; März, Christian; Matsuzaki, Kenji M; McClymont, Erin L; Moy, Chris; Müller, Juliane; Nakamura, Atsunori; Ojima, Takanori; Ribeiro, Fabiana R; Ridgway, Kenneth D; Romero, Oscar E; Slagle, Angela L; Stoner, Joseph S; St-Onge, Guillaume; Suto, Itsuki; Walczak, Maureen D; Worthington, Lindsay L; Bailey, Ian; Enkelmann, Eva; Reece, Robert; Swartz, John M

    2015-12-01

    Erosion, sediment production, and routing on a tectonically active continental margin reflect both tectonic and climatic processes; partitioning the relative importance of these processes remains controversial. Gulf of Alaska contains a preserved sedimentary record of the Yakutat Terrane collision with North America. Because tectonic convergence in the coastal St. Elias orogen has been roughly constant for 6 My, variations in its eroded sediments preserved in the offshore Surveyor Fan constrain a budget of tectonic material influx, erosion, and sediment output. Seismically imaged sediment volumes calibrated with chronologies derived from Integrated Ocean Drilling Program boreholes show that erosion accelerated in response to Northern Hemisphere glacial intensification (∼ 2.7 Ma) and that the 900-km-long Surveyor Channel inception appears to correlate with this event. However, tectonic influx exceeded integrated sediment efflux over the interval 2.8-1.2 Ma. Volumetric erosion accelerated following the onset of quasi-periodic (∼ 100-ky) glacial cycles in the mid-Pleistocene climate transition (1.2-0.7 Ma). Since then, erosion and transport of material out of the orogen has outpaced tectonic influx by 50-80%. Such a rapid net mass loss explains apparent increases in exhumation rates inferred onshore from exposure dates and mapped out-of-sequence fault patterns. The 1.2-My mass budget imbalance must relax back toward equilibrium in balance with tectonic influx over the timescale of orogenic wedge response (millions of years). The St. Elias Range provides a key example of how active orogenic systems respond to transient mass fluxes, and of the possible influence of climate-driven erosive processes that diverge from equilibrium on the million-year scale. PMID:26598689

  6. Mid-Pleistocene climate transition drives net mass loss from rapidly uplifting St. Elias Mountains, Alaska

    PubMed Central

    Jaeger, John M.; Mix, Alan C.; Asahi, Hirofumi; Bahlburg, Heinrich; Belanger, Christina L.; Berbel, Glaucia B. B.; Childress, Laurel; Cowan, Ellen; Drab, Laureen; Forwick, Matthias; Fukumura, Akemi; Ge, Shulan; Gupta, Shyam; Konno, Susumu; LeVay, Leah J.; März, Christian; McClymont, Erin L.; Moy, Chris; Müller, Juliane; Nakamura, Atsunori; Ojima, Takanori; Ribeiro, Fabiana R.; Ridgway, Kenneth D.; Romero, Oscar E.; Slagle, Angela L.; Stoner, Joseph S.; St-Onge, Guillaume; Suto, Itsuki; Walczak, Maureen D.; Worthington, Lindsay L.; Bailey, Ian; Enkelmann, Eva; Reece, Robert; Swartz, John M.

    2015-01-01

    Erosion, sediment production, and routing on a tectonically active continental margin reflect both tectonic and climatic processes; partitioning the relative importance of these processes remains controversial. Gulf of Alaska contains a preserved sedimentary record of the Yakutat Terrane collision with North America. Because tectonic convergence in the coastal St. Elias orogen has been roughly constant for 6 My, variations in its eroded sediments preserved in the offshore Surveyor Fan constrain a budget of tectonic material influx, erosion, and sediment output. Seismically imaged sediment volumes calibrated with chronologies derived from Integrated Ocean Drilling Program boreholes show that erosion accelerated in response to Northern Hemisphere glacial intensification (∼2.7 Ma) and that the 900-km-long Surveyor Channel inception appears to correlate with this event. However, tectonic influx exceeded integrated sediment efflux over the interval 2.8–1.2 Ma. Volumetric erosion accelerated following the onset of quasi-periodic (∼100-ky) glacial cycles in the mid-Pleistocene climate transition (1.2–0.7 Ma). Since then, erosion and transport of material out of the orogen has outpaced tectonic influx by 50–80%. Such a rapid net mass loss explains apparent increases in exhumation rates inferred onshore from exposure dates and mapped out-of-sequence fault patterns. The 1.2-My mass budget imbalance must relax back toward equilibrium in balance with tectonic influx over the timescale of orogenic wedge response (millions of years). The St. Elias Range provides a key example of how active orogenic systems respond to transient mass fluxes, and of the possible influence of climate-driven erosive processes that diverge from equilibrium on the million-year scale. PMID:26598689

  7. A grid of MHD models for stellar mass loss and spin-down rates of solar analogs

    SciTech Connect

    Cohen, O.; Drake, J. J.

    2014-03-01

    Stellar winds are believed to be the dominant factor in the spin-down of stars over time. However, stellar winds of solar analogs are poorly constrained due to observational challenges. In this paper, we present a grid of magnetohydrodynamic models to study and quantify the values of stellar mass loss and angular momentum loss rates as a function of the stellar rotation period, magnetic dipole component, and coronal base density. We derive simple scaling laws for the loss rates as a function of these parameters, and constrain the possible mass loss rate of stars with thermally driven winds. Despite the success of our scaling law in matching the results of the model, we find a deviation between the 'solar dipole' case and a real case based on solar observations that overestimates the actual solar mass loss rate by a factor of three. This implies that the model for stellar fields might require a further investigation with additional complexity. Mass loss rates in general are largely controlled by the magnetic field strength, with the wind density varying in proportion to the confining magnetic pressure B {sup 2}. We also find that the mass loss rates obtained using our grid models drop much faster with the increase in rotation period than scaling laws derived using observed stellar activity. For main-sequence solar-like stars, our scaling law for angular momentum loss versus poloidal magnetic field strength retrieves the well-known Skumanich decline of angular velocity with time, Ω{sub *}∝t {sup –1/2}, if the large-scale poloidal magnetic field scales with rotation rate as B{sub p}∝Ω{sub ⋆}{sup 2}.

  8. Burying a binary: Dynamical mass loss and a continuous optically thick outflow explain the candidate stellar merger V1309 Scorpii

    SciTech Connect

    Pejcha, Ondřej

    2014-06-10

    V1309 Sco was proposed to be a stellar merger and a common envelope transient based on the pre-outburst light curve of a contact eclipsing binary with a rapidly decaying orbital period. Using published data, I show that the period decay timescale P/ P-dot of V1309 Sco decreased from ∼1000 to ∼170 yr in ≲ 6 yr, which implies a very high value of P{sup ¨}. I argue that V1309 Sco experienced an onset of dynamical mass loss through the outer Lagrange point, which eventually obscured the binary. The photosphere of the resulting continuous optically thick outflow expands as the mass-loss rate increases, explaining the ∼200 day rise to optical maximum. The model yields the mass-loss rate of the binary star as a function of time and fits the observed light curve remarkably well. It is also possible to observationally constrain the properties of the surface layers undergoing the dynamical mass loss. V1309 Sco is thus a prototype of a new class of stellar transients distinguished by a slow rise to optical maximum that are driven by dynamical mass loss from a binary. I discuss the implications of these findings for stellar transients and other suggested common envelope events.

  9. A Fe-C coated long-period fiber grating sensor for corrosion-induced mass loss measurement.

    PubMed

    Chen, Yizheng; Tang, Fujian; Bao, Yi; Tang, Yan; Chen, Genda

    2016-05-15

    This Letter reports a Fe-C coated long period fiber gratings sensor with a grating period of 387±0.1  μm for corrosion monitoring of low carbon steel in a 3.5 wt. % NaCl solution. An LPFG sensor was first deposited with a 0.8 μm thick layer of silver (Ag) and then electroplated with a 20 μm thick Fe-C coating. The chemical composition of the Fe-C coating was designed to include the main elements of low carbon steel. The resonant wavelength of the coated sensor was correlated with the mass loss of steel over time. Test results indicated a corrosion sensitivity of 0.0423 nm per 1% mass loss up to 80% Fe-C mass loss and 0.576 nm per 1% mass loss between 80% and 95% Fe-C mass loss. The corrosion sensitivity of such a Fe-C coated LPFG sensor was a trade-off for the service life of the sensor, both depending on thicknesses of the inner silver layer and the outer Fe-C coating. PMID:27176989

  10. Multi-decadal mass loss of glaciers in the Everest area (Nepal Himalaya) derived from stereo imagery

    NASA Astrophysics Data System (ADS)

    Bolch, T.; Pieczonka, T.; Benn, D. I.

    2011-04-01

    Mass loss of Himalayan glaciers has wide-ranging consequences such as changing runoff distribution, sea level rise and an increasing risk of glacial lake outburst floods (GLOFs). The assessment of the regional and global impact of glacier changes in the Himalaya is, however, hampered by a lack of mass balance data for most of the range. Multi-temporal digital terrain models (DTMs) allow glacier mass balance to be calculated. Here, we present a time series of mass changes for ten glaciers covering an area of about 50 km2 south and west of Mt. Everest, Nepal, using stereo Corona spy imagery (years 1962 and 1970), aerial images and recent high resolution satellite data (Cartosat-1). This is the longest time series of mass changes in the Himalaya. We reveal that the glaciers have been significantly losing mass since at least 1970, despite thick debris cover. The specific mass loss for 1970-2007 is 0.32 ± 0.08 m w.e. a-1, however, not higher than the global average. Comparisons of the recent DTMs with earlier time periods indicate an accelerated mass loss. This is, however, hardly statistically significant due to high uncertainty, especially of the lower resolution ASTER DTM. The characteristics of surface lowering can be explained by spatial variations of glacier velocity, the thickness of the debris-cover, and ice melt due to exposed ice cliffs and ponds.

  11. Calibration of Post-AGB Supergiants as Standard Extragalactic Candles for HST

    NASA Technical Reports Server (NTRS)

    Bond, Howard E.

    1998-01-01

    This report summarizes activities carried out with support from the NASA Ultraviolet, Visible, and Gravitational Astrophysics Research and Analysis Program. The aim of the program is to calibrate the absolute magnitudes of post-asymptotic-giant-branch (post-AGB or PAGB) stars, which we believe will be an excellent new "standard candle" for measuring extragalactic distances. The reason for this belief is that in old populations, the stars that are evolving through the PAGB region of the HR (Hertzsprung-Russell) diagram arise from only a single main-sequence turnoff mass. In addition, the theoretical PAGB evolutionary tracks show that they evolve through this region at constant luminosity; hence the PAGB stars should have an extremely narrow luminosity function. Moreover, as the PAGB stars evolve through spectral types F and A (en route from the AGB to hot stellar remnants and white dwarfs), they have the highest luminosities attained by old stars (both bolometrically and in the visual band). Finally, the PAGB stars of these spectral types are very easily identified, due to their large Balmer jumps, which are due to their very low surface gravities.

  12. Modeling of Camembert-type cheese mass loss in a ripening chamber: main biological and physical phenomena.

    PubMed

    Hélias, A; Mirade, P-S; Corrieu, G

    2007-11-01

    A model of the mass loss of Camembert-type cheese was established with data obtained from 2 experimental ripening trials carried out in 2 pilot ripening chambers. During these experiments, a cheese was continuously weighed and the relative humidity, temperature, oxygen, and carbon dioxide concentrations in the ripening chamber were recorded online. The aim was to establish a simple but accurate model that would predict cheese mass changes according to available online measurements. The main hypotheses were that 1) the cheese water activity was constant during ripening, 2) the respiratory activity of the microflora played a major role by inducing heat production, combined with important water evaporation, 3) the temperature gradient existing inside the cheese was negligible, and the limiting phenomenon was the convective transfer. The water activity and the specific heat of the cheeses were assessed by offline measurements. The others parameters in the model were obtained from the literature. This dynamic model was built with 2 state variables: the cheese mass and the surface temperature of the cheese. In this way, only the heat transfer coefficient had to be fitted, and it was strongly determined by the airflow characteristics close to the cheeses. Model efficiency was illustrated by comparing the estimated and measured mass and the mass loss rate for the 2 studied runs; the relative errors were less than 1.9 and 3.2% for the mass loss and the mass loss rate, respectively. The dynamic effects of special events, such as room defrosting or changes in chamber relative humidity, were well described by the model, especially in terms of kinetics (mass loss rates). PMID:17954773

  13. Exploring the Onset of the Contribution of the First AGB Stars to the Galactic Chemical Enrichment using Isotopic Ratios

    NASA Astrophysics Data System (ADS)

    Goswami, A.

    2015-08-01

    There is uncertainty over the time at which the first intermediate and low-mass stars reach the AGB phase and begin to influence their environments with the products of nucleosynthesis. While some studies have indicated that enrichment from AGB stars sets in at a time corresponding to -2.4 < [Fe/H] < -2.1, others suggest a time as early as [Fe/H] ≍ -2.75. These suggestions come from observations of s-process heavy elements in old metal-poor stars. Measurements of stellar isotopic ratios, such as the Mg isotope ratios, can also be a useful probe to explore the contribution of AGB stars to the Galactic chemical inventory. However, measurements of isotopic ratios require spectra with high resolution (R > 90 000) and high S/N ratios (> 200) which require very long exposure times with the existing observing facilities. Upcoming large telescopes of 25 to 42-m size equipped with high resolution spectrographs will provide the resolution and sensitivity required for measurements of isotopic ratios that are fundamental indicators of nucleosynthesis.

  14. Rapid Ice Mass Loss: Does It Have an Influence on Earthquake Occurrence in Southern Alaska?

    NASA Technical Reports Server (NTRS)

    Sauber, Jeanne M.

    2008-01-01

    The glaciers of southern Alaska are extensive, and many of them have undergone gigatons of ice wastage on time scales on the order of the seismic cycle. Since the ice loss occurs directly above a shallow main thrust zone associated with subduction of the Pacific-Yakutat plate beneath continental Alaska, the region between the Malaspina and Bering Glaciers is an excellent test site for evaluating the importance of recent ice wastage on earthquake faulting potential. We demonstrate the influence of cumulative glacial mass loss following the 1899 Yakataga earthquake (M=8.1) by using a two dimensional finite element model with a simple representation of ice fluctuations to calculate the incremental stresses and change in the fault stability margin (FSM) along the main thrust zone (MTZ) and on the surface. Along the MTZ, our results indicate a decrease in FSM between 1899 and the 1979 St. Elias earthquake (M=7.4) of 0.2 - 1.2 MPa over an 80 km region between the coast and the 1979 aftershock zone; at the surface, the estimated FSM was larger but more localized to the lower reaches of glacial ablation zones. The ice-induced stresses were large enough, in theory, to promote the occurrence of shallow thrust earthquakes. To empirically test the influence of short-term ice fluctuations on fault stability, we compared the seismic rate from a reference background time period (1988-1992) against other time periods (1993-2006) with variable ice or tectonic change characteristics. We found that the frequency of small tectonic events in the Icy Bay region increased in 2002-2006 relative to the background seismic rate. We hypothesize that this was due to a significant increase in the rate of ice wastage in 2002-2006 instead of the M=7.9, 2002 Denali earthquake, located more than 100km away.

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

    SciTech Connect

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

    2014-02-10

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

  16. Temperature evolution and mass losses during immersion vacuum cooling of cooked beef joints - A finite difference model.

    PubMed

    Drummond, Liana; Sun, Da-Wen

    2008-11-01

    A finite difference model was developed to describe and predict the temperature and mass loss evolution in reconstructed beef joints during immersion vacuum cooling. Fast cooling is obtained within beef pores and at beef surface when evaporation in the surrounding liquid is high. The cooling rate diminishes as the vacuum chamber pressure stabilizes and the liquid temperature reaches its lower value. The maximum deviation between measured and calculated temperatures was within 5°C for the beef (core and surface) and within 7°C for the surrounding liquid (measured at the bottom of the container). Absolute differences between predicted and experimental mass losses for the liquid and beef sample were around 2% and 1%, respectively. Mass losses are higher during the first period when evaporation is the main mode of heat transfer. Mechanical agitation in the surrounding liquid is suggested as a way to further reduce cooling times and to prevent uneven cooling. PMID:22063613

  17. Searching for heavily obscured post-AGB stars and planetary nebulae. II. Near-IR observations of IRAS sources

    NASA Astrophysics Data System (ADS)

    Ramos-Larios, G.; Guerrero, M. A.; Suárez, O.; Miranda, L. F.; Gómez, J. F.

    2012-09-01

    The most massive AGB stars are expected to result in heavily obscured post-AGB stars, proto-PNe and PNe with highly axisymmetric morphologies. To investigate this evolutionary connection, we have selected a sample of 165 presumably obscured IRAS post-AGB star and PN candidates and obtained near-IR JHK images for 164 of them. These images, in conjunction with DSS, 2MASS, Spitzer GLIMPSE, MSX, AKARI, and IRAS archival data, have allowed us to identify the near-IR counterparts of 154 of these sources, providing reliable finding charts and coordinates. Near-IR narrow-band Brγ, H2, and K continuum images were acquired for 6 of these sources that were found to be resolved in near-IR JHK images. Among the extended post-AGB source and PN candidates, three are round and seven have bipolar morphologies. Five of the extended sources are ionized and may have thus entered the PN stage. We note that all extended sources with water maser emission have bipolar morphology. We have investigated the Galactic distribution of sources with the largest flux drop from the 9 μm AKARI band to the near-IR J band and found that the width of the distribution in Galactic latitude is consistent with those of bipolar PNe and DUPLEX (DUst-Prominent Longitudinally EXtended) sources. Based on observations collected at the European Organization for Astronomical Research in the Southern Hemisphere, Chile (081.D-0812), observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundación Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, and on observations with AKARI, a JAXA project with the participation of ESA.

  18. Radio Observations Reveal the Mass Loss History of Type Ibc Supernova Progenitors

    NASA Astrophysics Data System (ADS)

    Wellons, Sarah; Soderberg, A. M.

    2011-01-01

    We present extensive radio observations of the nearby Type Ibc supernovae 2004cc, 2004gq, and 2004dk spanning Δ t≈ 8-1800 days after explosion. Using a dynamical model developed for synchrotron emission from a slightly decelerated blastwave, we estimate the velocity and energy of the fastest ejecta and the density profile of the circumstellar medium. The blastwaves for all three supernovae are characterized by non-relativistic velocities of v≈ (0.1-25)c and associated energies of E≈ (2-10)× 1047 erg, in line with the expectations for a typical homologous explosion. Smooth, stellar wind density profiles are indicated by the early radio data and we estimate the progenitor mass loss rates to be ∘ M≈ (8-40)× 10-6 M⊙ yr-1 (wind velocity, vw=103 km s-1). These properties are consistent with those of Wolf-Rayet stars, the favored progenitors of SNe Ibc including those associated with long-duration gamma-ray bursts. However, at late time, each of these SNe show evidence for abrupt radio variability which we attribute to significant circumstellar density modulations (factor of 5-100) at radii of R≈ (1-50)× 1016 cm. For SN 2004gq, the density modulations are marginally consistent with the expectations for a variable and/or clumpy Wolf-Rayet line-driven wind. However, in the case of SNe 2004cc and 2004dk, the density modulations are more intense, ∘ M>/ 10-4M⊙ yr-1, and possibly attributed to continuum-driven winds or hydrodynamic eruptions. We compare the circumstellar environments for these three SNe with those of other Type Ibc supernovae and nearby gamma-ray bursts and find that they are characterized by a more violent progenitor mass loss history in the decades leading up to explosion. This work is supported in part by the NSF REU and DOD ASSURE programs under NSF grant no. 0754568 and by the Smithsonian Institution.

  19. OBSERVATIONS OF MASS LOSS FROM THE TRANSITING EXOPLANET HD 209458b

    SciTech Connect

    Linsky, Jeffrey L.; Yang Hao; France, Kevin; Froning, Cynthia S.; Green, James C.; Stocke, John T.; Osterman, Steven N. E-mail: haoyang@jilau1.colorado.ed E-mail: cfroning@casa.colorado.ed E-mail: stocke@casa.colorado.ed

    2010-07-10

    Using the new Cosmic Origins Spectrograph on the Hubble Space Telescope, we obtained moderate-resolution, high signal/noise ultraviolet spectra of HD 209458 and its exoplanet HD 209458b during transit, both orbital quadratures, and secondary eclipse. We compare transit spectra with spectra obtained at non-transit phases to identify spectral features due to the exoplanet's expanding atmosphere. We find that the mean flux decreased by 7.8% {+-} 1.3% for the C II 1334.5323 A and 1335.6854 A lines and by 8.2% {+-} 1.4% for the Si III 1206.500 A line during transit compared to non-transit times in the velocity interval -50 to +50 km s{sup -1}. Comparison of the C II and Si III line depths and transit/non-transit line ratios shows deeper absorption features near -10 and +15 km s{sup -1} and less certain features near -40 and +30-70 km s{sup -1}, but future observations are needed to verify this first detection of velocity structure in the expanding atmosphere of an exoplanet. Our results for the C II lines and the non-detection of Si IV 1394.76 A absorption are in agreement with Vidal-Madjar et al., but we find absorption during transit in the Si III line contrary to the earlier result. The 8% {+-} 1% obscuration of the star during transit is far larger than the 1.5% obscuration by the exoplanet's disk. Absorption during transit at velocities between -50 and +50 km s{sup -1} in the C II and Si III lines requires high-velocity ion absorbers. Assuming hydrodynamic model values for the gas temperature and outflow velocity at the limb of the outflow as seen in the C II lines, we find mass-loss rates in the range (8-40)x10{sup 10} g s{sup -1}. These rates assume that the carbon abundance is solar, which is not the case for the giant planets in the solar system. Our mass-loss rate estimate is consistent with theoretical hydrodynamic models that include metals in the outflowing gas.

  20. Searching for the Missing Mass in Very Young Preplanetary Nebulae

    NASA Astrophysics Data System (ADS)

    Sahai, Raghvendra; Claussen, Mark; Morris, Mark; Sanchez Contreras, Carmen

    2005-06-01

    Pre-Planetary nebulae (PPNe), objects in transition between the AGB and planetary nebula (PN) evolutionary phases, hold the key to our understanding of the late evolutionary stages of low and intermediate mass stars. Essentially all well-characterized PPNe are bipolar, whereas the mass-loss envelopes of AGB stars are strikingly spherical -- we find that almost all the targets observed in our HST surveys of young PPNe (yPPNe) which are resolved, show well-defined bipolar or multipolar morphologies. We have hypothesized that it is the hydrodynamic interaction of fast, tenuous collimated flows with the dense, cool massive envelope ejected during the AGB phase, which is responsible for shaping these objects. The bulk of the nebular mass in this envelope, is however not seen in the HST data, since much of it resides in a cool, dusty, molecular component surrounding the central aspherical nebula. Thus a crucial ingredient for theoretical studies of such interactions is lacking for a majority of the yPPNe discovered in our HST surveys. We propose to use IRAC, IRS & MIPS to characterise the infrared spectrum of a selected sample (16) of such objects from short to long wavelengths, as a primary probe of the total circumstellar mass. Detailed spectra and full SEDs are necessary in order to derive the total dust mass, which depends sensitively on the radial temperature distribution and can only be determined accurately by modeling the full infrared spectrum of these objects. Our spectra should also show specific dust features (e.g. silicate feature in absorption) which act as probes of different structural components (e.g. a central equatorial disk) and unusual physical processes (e.g. growth of icy grain mantles) in these objects, and constrain uncertainties in the dust properties (emissivity law, composition), which also affect the mass determination.

  1. Adiabatic Mass Loss in Binary Stars. II. From Zero-age Main Sequence to the Base of the Giant Branch

    NASA Astrophysics Data System (ADS)

    Ge, Hongwei; Webbink, Ronald F.; Chen, Xuefei; Han, Zhanwen

    2015-10-01

    In the limit of extremely rapid mass transfer, the response of a donor star in an interacting binary becomes asymptotically one of adiabatic expansion. We survey here adiabatic mass loss from Population I stars (Z = 0.02) of mass 0.10 M⊙-100 M⊙ from the zero-age main sequence to the base of the giant branch, or to central hydrogen exhaustion for lower main sequence stars. The logarithmic derivatives of radius with respect to mass along adiabatic mass-loss sequences translate into critical mass ratios for runaway (dynamical timescale) mass transfer, evaluated here under the assumption of conservative mass transfer. For intermediate- and high-mass stars, dynamical mass transfer is preceded by an extended phase of thermal timescale mass transfer as the star is stripped of most of its envelope mass. The critical mass ratio qad (throughout this paper, we follow the convention of defining the binary mass ratio as q ≡ Mdonor/Maccretor) above which this delayed dynamical instability occurs increases with advancing evolutionary age of the donor star, by ever-increasing factors for more massive donors. Most intermediate- or high-mass binaries with nondegenerate accretors probably evolve into contact before manifesting this instability. As they approach the base of the giant branch, however, and begin developing a convective envelope, qad plummets dramatically among intermediate-mass stars, to values of order unity, and a prompt dynamical instability occurs. Among low-mass stars, the prompt instability prevails throughout main sequence evolution, with qad declining with decreasing mass, and asymptotically approaching qad = 2/3, appropriate to a classical isentropic n = 3/2 polytrope. Our calculated qad values agree well with the behavior of time-dependent models by Chen & Han of intermediate-mass stars initiating mass transfer in the Hertzsprung gap. Application of our results to cataclysmic variables, as systems that must be stable against rapid mass transfer, nicely

  2. Dietary sodium citrate supplementation enhances rehydration and recovery from rapid body mass loss in trained wrestlers.

    PubMed

    Timpmann, Saima; Burk, Andres; Medijainen, Luule; Tamm, Maria; Kreegipuu, Kairi; Vähi, Mare; Unt, Eve; Oöpik, Vahur

    2012-12-01

    This study assessed the effects of dietary sodium citrate supplementation during a 16 h recovery from 5% rapid body mass loss (RBML) on physiological functions, affective state, and performance in trained wrestlers. Sixteen wrestlers performed an upper body intermittent sprint performance (UBISP) test under three conditions: before RBML, after RBML, and after a 16 h recovery from RBML. During recovery, the subjects ate a prescribed diet supplemented with sodium citrate (600 mg·kg(-1); CIT group, N = 8) or placebo (PLC group, N = 8) and drank water ad libitum. RBML reduced (p < 0.05) UBISP mean power and increased urine specific gravity (USG). Reduction in mean power was associated with changes in plasma volume (PV) (r = 0.649, p = 0.006) and USG (r = -0.553, p = 0.026). During the 16 h recovery, increases in body mass (BM) and PV were greater (p < 0.05) in the CIT group than in the PLC group. BM gain was associated with water retention in the CIT group (r = 0.899, p = 0.002) but not in the PLC group (r = 0.335, p = 0.417). Blood pH, HCO(3)(-) concentration, and base excess increased (p < 0.05) only in the CIT group. Changes in UBISP, general negative affect, and general positive affect did not differ in the two groups. In conclusion, ingestion of sodium citrate increases blood buffering capacity and PV and stimulates BM regain during a 16 h recovery from RBML in trained wrestlers. However, sodium citrate does not improve UBISP nor does it have an impact on the affective state. PMID:22871128

  3. The sensitivity of harassment to orbit: mass loss from early-type dwarfs in galaxy clusters

    NASA Astrophysics Data System (ADS)

    Smith, R.; Sánchez-Janssen, R.; Beasley, M. A.; Candlish, G. N.; Gibson, B. K.; Puzia, T. H.; Janz, J.; Knebe, A.; Aguerri, J. A. L.; Lisker, T.; Hensler, G.; Fellhauer, M.; Ferrarese, L.; Yi, S. K.

    2015-12-01

    We conduct a comprehensive numerical study of the orbital dependence of harassment on early-type dwarfs consisting of 168 different orbits within a realistic, Virgo-like cluster, varying in eccentricity and pericentre distance. We find harassment is only effective at stripping stars or truncating their stellar discs for orbits that enter deep into the cluster core. Comparing to the orbital distribution in cosmological simulations, we find that the majority of the orbits (more than three quarters) result in no stellar mass loss. We also study the effects on the radial profiles of the globular cluster systems of early-type dwarfs. We find these are significantly altered only if harassment is very strong. This suggests that perhaps most early-type dwarfs in clusters such as Virgo have not suffered any tidal stripping of stars or globular clusters due to harassment, as these components are safely embedded deep within their dark matter halo. We demonstrate that this result is actually consistent with an earlier study of harassment of dwarf galaxies, despite the apparent contradiction. Those few dwarf models that do suffer stellar stripping are found out to the virial radius of the cluster at redshift = 0, which mixes them in with less strongly harassed galaxies. However when placed on phase-space diagrams, strongly harassed galaxies are found offset to lower velocities compared to weakly harassed galaxies. This remains true in a cosmological simulation, even when haloes have a wide range of masses and concentrations. Thus phase-space diagrams may be a useful tool for determining the relative likelihood that galaxies have been strongly or weakly harassed.

  4. Mass loss of TEOS-coated RCC subjected to the environment at the shuttle wing leading edge

    NASA Technical Reports Server (NTRS)

    Stroud, C. W.; Rummler, D. R.

    1981-01-01

    Coated, reinforced carbon-carbon (RCC) is used for the leading edges of the Space Shuttle. The mass loss characteristics of RCC specimens coated with tetra-ethyl-ortho-silicate (TEOS) were determined for conditions which simulated the entry environment expected at the stagnation area of the wing leading edge. Maximum specimen temperature was 1632 K. Specimens were exposed for up to 100 missions. Stress levels up to 8.274 MPa caused an average increase in oxidation of 6 percent over unstressed specimens. Experimentally determined mass losses were compared with those predicted by an existing empirical analysis.

  5. Dramatic mass loss in extreme high-elevation areas of a western Himalayan glacier: observations and modeling

    PubMed Central

    Zhao, Huabiao; Yang, Wei; Yao, Tandong; Tian, Lide; Xu, Baiqing

    2016-01-01

    Rapid climate change at high elevations has accelerated glacier retreat in the Himalayas and Tibetan Plateau. However, due to the lack of long-term glaciological measurements, there are still uncertainties regarding when the mass loss began and what the magnitude of mass loss is at such high elevations. Based on in situ glaciological observations during the past 9 years and a temperature-index mass balance model, this study investigates recent mass loss of the Naimona’nyi Glacier in the western Himalayas and reconstructs a 41-year (1973/74–2013/14) equilibrium line altitude (ELA) and glacier-wide mass loss. The result indicates that even at 6000 m above sea level (a.s.l.), the annual mass loss reaches ~0.73 m water equivalent (w.e.) during the past 9 years. Concordant with the abrupt climate shift in the end of 1980s, the ELA has dramatically risen from ~5969 ± 73 m a.s.l. during 1973/74–1988/89 to ~6193 ± 75 m a.s.l. during 1989/90–2013/14, suggesting that future ice cores containing uninterrupted climate records could only be recovered at least above 6200 m a.s.l. in the Naimona’nyi region. The glacier-wide mass balance over the past 41 years is averaged to be approximately −0.40 ± 0.17 m w.e., exhibiting a significant increase in the decadal average from −0.01 ± 0.15 to −0.69 ± 0.21 m w.e. PMID:27561411

  6. Dramatic mass loss in extreme high-elevation areas of a western Himalayan glacier: observations and modeling.

    PubMed

    Zhao, Huabiao; Yang, Wei; Yao, Tandong; Tian, Lide; Xu, Baiqing

    2016-01-01

    Rapid climate change at high elevations has accelerated glacier retreat in the Himalayas and Tibetan Plateau. However, due to the lack of long-term glaciological measurements, there are still uncertainties regarding when the mass loss began and what the magnitude of mass loss is at such high elevations. Based on in situ glaciological observations during the past 9 years and a temperature-index mass balance model, this study investigates recent mass loss of the Naimona'nyi Glacier in the western Himalayas and reconstructs a 41-year (1973/74-2013/14) equilibrium line altitude (ELA) and glacier-wide mass loss. The result indicates that even at 6000 m above sea level (a.s.l.), the annual mass loss reaches ~0.73 m water equivalent (w.e.) during the past 9 years. Concordant with the abrupt climate shift in the end of 1980s, the ELA has dramatically risen from ~5969 ± 73 m a.s.l. during 1973/74-1988/89 to ~6193 ± 75 m a.s.l. during 1989/90-2013/14, suggesting that future ice cores containing uninterrupted climate records could only be recovered at least above 6200 m a.s.l. in the Naimona'nyi region. The glacier-wide mass balance over the past 41 years is averaged to be approximately -0.40 ± 0.17 m w.e., exhibiting a significant increase in the decadal average from -0.01 ± 0.15 to -0.69 ± 0.21 m w.e. PMID:27561411

  7. Ice mass loss in Greenland, the Gulf of Alaska, and the Canadian Archipelago: Seasonal cycles and decadal trends

    NASA Astrophysics Data System (ADS)

    Harig, Christopher; Simons, Frederik J.

    2016-04-01

    Over the past several decades mountain glaciers and ice caps have been significant contributors to sea level rise. Here we estimate the ice mass changes in the Canadian Archipelago, the Gulf of Alaska, and Greenland since 2003 by analyzing time-varying gravimetry data from the Gravity Recovery and Climate Experiment. Prior to 2013, interannual ice mass variability in the Gulf of Alaska and in regions around Greenland remains within the average estimated over the whole data span. Beginning in summer 2013, ice mass in regions around Greenland departs positively from its long-term trend. Over Greenland this anomaly reached almost 500 Gt through the end of 2014. Overall, long-term ice mass loss from Greenland and the Canadian Archipelago continues to accelerate, while losses around the Gulf of Alaska region continue but remain steady with no significant acceleration.

  8. FUV Spectra of Evolved Late-K and M Stars: Mass Loss Revisited and Stellar Activity

    NASA Technical Reports Server (NTRS)

    Harper, Graham M.

    2002-01-01

    This is the final report for the FUSE Cycle 1 program A100: FUV Spectra of Evolved Late-K and M Stars: Mass Loss revisited and Stellar Activity. Targets alpha TrA (K3 II) and gamma Cru (M3 III) were originally assigned 25 ksec each, to be observed in the medium aperture. Once the in-flight performance and telescope alignment problems were known, the observations were reprogrammed to optimized the scientific return of the program. Alpha TrA was scheduled for 25 ksec observations in both the medium and large apertures. The principle aim of this program was to measure the stellar FUV line and continuum emission, in order to estimate the photoionization radiation field and to determine the level of stellar activity through the fluxes in the collisionally excited high temperature diagnostics: C III 977Angstroms and O VI 1032,1038Angstrom doublet. The medium aperture observations were obtained successfully while the large aperture observations were thought by Johns Hopkins University (JHU)to be lost to satellite problems. There was insufficient signal-to- noise in the medium aperture short wavelength Sic channels to do quantitative science.

  9. Body mass loss correlates with cognitive performance in primates under acute caloric restriction conditions.

    PubMed

    Villain, N; Picq, J-L; Aujard, F; Pifferi, F

    2016-05-15

    Brain functions are known to consume high levels of energy, thus, the integrity of cognitive performance can be drastically impacted by acute caloric restriction. In this study, we tested the impact of a 40% caloric restriction on the cognitive abilities of the grey mouse lemur (Microcebus murinus). Twenty-three male mouse lemurs were divided into two groups: 13 control animals (CTL) that were fed with 105kJ/day and 10calorie restricted (CR) animals that received 40% less food (63kJ/day) than the CTL animals. The animals were fed according to their group for 19days. Before treatment, we assessed baseline associative learning capacities, resting metabolic rates and locomotor performance of both animal groups. After treatment, we tested the same functions as well as long-term memory. Our results showed that CR animals had lower learning performance following caloric restriction. The effects of caloric restriction on memory recall varied and depended on the metabolism of the individual animal. Body mass loss was linked to memory test performance in the CR group, and lower performance was observed in individuals losing the most weight. While CR was observed to negatively impact learning, locomotor capacities were preserved in CR animals, and there were higher resting metabolic rates in the CR group. Our data reinforce the strong link between energy allocation and brain function, and suggest that in the context of food shortage, learning capacities could be a limiting parameter in the adaptation to a changing environment. PMID:26952885

  10. Photometry of SN 2002ic and implications for the progenitor mass-loss history

    SciTech Connect

    Wood-Vasey, W.M.; Wang, L.; Aldering, G.

    2004-05-06

    We present new pre-maximum and late-time optical photometry of the Type Ia/IIn supernova 2002ic. These observations are combined with the published V-band magnitudes of Hamuy et al. (2003) and the VLT spectrophotometry of Wang et al. (2004) to construct the most extensive light curve to date of this unusual supernova. The observed flux at late time is significantly higher relative to the flux at maximum than that of any other observed Type Ia supernova and continues to fade very slowly a year after explosion. Our analysis of the light curve suggests that a non-Type Ia supernova component becomes prominent {approx}20 days after explosion. Modeling of the non-Type Ia supernova component as heating from the shock interaction of the supernova ejecta with pre-existing circumstellar material suggests the presence of a {approx}1.7 x 1015 cm gap or trough between the progenitor system and the surrounding circumstellar material. This gap could be due to significantly lower mass-loss {approx}15 (nu{sub omega}/10 km/s) -1 years prior to explosion or evacuation of the circumstellar material by a low-density fast wind. The latter is consistent with observed properties of proto-planetary nebulae and with models of white-dwarf + asymptotic giant branch star progenitor systems with the asymptotic giant branch star in the proto-planetary nebula phase.

  11. Intermittent dust mass loss from activated asteroid P/2013 P5 (PANSTARRS)

    SciTech Connect

    Moreno, F.; Pozuelos, F.

    2014-02-01

    We present observations and models of the dust environment of activated asteroid P/2013 P5 (PANSTARRS). The object displayed a complex morphology during the observations, with the presence of multiple tails. We combined our own observations, all made with instrumentation attached to the 10.4 m Gran Telescopio Canarias on La Palma, with previously published Hubble Space Telescope images to build a model aimed at fitting all the observations. Altogether, the data cover a full three month period of observations which can be explained by intermittent dust loss. The most plausible scenario is that of an asteroid rotating with the spinning axis oriented perpendicular to the orbit plane and losing mass from the equatorial region, consistent with rotational break-up. Assuming that the ejection velocity of the particles (v ∼ 0.02-0.05 m s{sup –1}) corresponds to the escape velocity, the object diameter is constrained to ∼30-130 m for bulk densities 3000-1000 kg m{sup –3}.

  12. Towards a coherent view of mass loss in Betelgeuse from the photosphere to the interstellar medium

    NASA Astrophysics Data System (ADS)

    Montarges, Miguel; Kervella, Pierre; Perrin, Guy

    2013-06-01

    Massive evolved stars contribute to the chemical enrichment of the interstellar medium (ISM), the Galaxy and ultimately the Universe through their mass loss. From the photosphere to the ISM, large convective motions, low surface gravity and high brightness combine to trigger an intense stellar wind. The released material evolves chemically as the distance from the star increases, and eventually forms dust particles. The involved physical and chemical processes are central to apprehend the cosmic impact of massive evolved stars, but they are poorly understood: the surface convection remains essentially uncharacterized, as the composition of the wind, and the role of the magnetic field is unknown. Betelgeuse is the closest red supergiant and therefore it stands out as the best candidate to obtain detailed observations of the close circumstellar environment of a massive evolved star. We are currently running a high angular resolution observations program to obtain a multi-wavelength and multi-epoch characterisation of this star. Using the IOTA interferometer, Haubois et al. reconstructed an image of the photosphere of the star. Within 1 to 100 stellar radii, the VLT and VLTI allowed us to probe the compact molecular envelope of Betelgeuse (the MOLsphere) in the near-infrared, and the extended dusty envelope in the thermal infrared domain. They were recently completed with HST/STIS observations of the chromosphere in the UV, whose location is surprisingly coincident with the MOLsphere. We will present a brief review of our recent results and of our ongoing work on Betelgeuse.

  13. Swimming Activity Prevents the Unloading Induced Loss of Bone Mass, Architecture, and Strength in Rats

    PubMed Central

    Falcai, Maurício J.; Leoni, Graziela Bianchi; de Sousa Neto, Manoel Damião; Volpon, Jose B.

    2015-01-01

    We investigated whether swimming activity associated with a three-week period of hypoactivity could prevent the deleterious effects of disuse on the tibias of tail-suspended rats. Forty Wistar rats were divided into five groups: (HS) permanently hindlimb suspension rats; (HS + Swim) rats submitted to unloading interrupted by swimming exercise; (HS + WB) hindlimb suspension rats with interruption for regular weight bearing for the same length of time as the HS+Swim rats; (Control) control rats that were allowed regular cage activities; and (Control + Swim) control rats that underwent swimming exercise. At the end of the experiment, bone mineral density, bone strength, and trabecular quantification were analyzed. The hindlimb-suspended rats exhibited bone quality loss (significant decrease in BMD, bone strength, and deterioration of trabecular and cortical bone architecture; decrease in BV/TV, TbN, TbTh, ConnD, CtV, and CtTh; and increase in TbSp) when compared to control rats. In contrast, trained rats showed a significant increase of 43% in bone mass, 29% in bone strength, 58% in trabecular thickness, 85% in bone volume, 27% in trabeculae number, and 30% in cortical volume, when compared to the hindlimb-suspended rats. We conclude that swimming activity not only ameliorates but also fully prevents the deleterious effects on bone quality in osteopenic rats. PMID:26090414

  14. Sea-level feedback lowers projections of future Antarctic Ice-Sheet mass loss.

    PubMed

    Gomez, Natalya; Pollard, David; Holland, David

    2015-01-01

    The stability of marine sectors of the Antarctic Ice Sheet (AIS) in a warming climate has been identified as the largest source of uncertainty in projections of future sea-level rise. Sea-level fall near the grounding line of a retreating marine ice sheet has a stabilizing influence on the ice sheets, and previous studies have established the importance of this feedback on ice age AIS evolution. Here we use a coupled ice sheet-sea-level model to investigate the impact of the feedback mechanism on future AIS retreat over centennial and millennial timescales for a range of emission scenarios. We show that the combination of bedrock uplift and sea-surface drop associated with ice-sheet retreat significantly reduces AIS mass loss relative to a simulation without these effects included. Sensitivity analyses show that the stabilization tends to be greatest for lower emission scenarios and Earth models characterized by a thin elastic lithosphere and low-viscosity upper mantle, as is the case for West Antarctica. PMID:26554381

  15. Sea-level feedback lowers projections of future Antarctic Ice-Sheet mass loss

    NASA Astrophysics Data System (ADS)

    Gomez, Natalya; Pollard, David; Holland, David

    2015-11-01

    The stability of marine sectors of the Antarctic Ice Sheet (AIS) in a warming climate has been identified as the largest source of uncertainty in projections of future sea-level rise. Sea-level fall near the grounding line of a retreating marine ice sheet has a stabilizing influence on the ice sheets, and previous studies have established the importance of this feedback on ice age AIS evolution. Here we use a coupled ice sheet-sea-level model to investigate the impact of the feedback mechanism on future AIS retreat over centennial and millennial timescales for a range of emission scenarios. We show that the combination of bedrock uplift and sea-surface drop associated with ice-sheet retreat significantly reduces AIS mass loss relative to a simulation without these effects included. Sensitivity analyses show that the stabilization tends to be greatest for lower emission scenarios and Earth models characterized by a thin elastic lithosphere and low-viscosity upper mantle, as is the case for West Antarctica.

  16. On the sensitivity of extrasolar mass-loss rate ranges: HD 209458b a case study

    NASA Astrophysics Data System (ADS)

    Villarreal D'Angelo, C. S.; Schneiter, M.; Costa, A.; Velázquez, P.; Raga, A.; Esquivel, A.

    2014-10-01

    We present a 3D hydrodynamic study of the effect that different stellar wind conditions and planetary wind structures have on the calculated Lyα absorptions during the transit of HD209458b. We approach the problem using 3D hydrodynamic simulations. Considering a range of stellar wind speeds ˜ [350-800] km s^{-1}, coronal temperature ˜ [3-7] × 10^{6} K and two values of the polytropic index Γ ˜ [1.01-1.13], while keeping fixed the stellar mass loss rate, we found a that a M_{p} range between ˜ [3-5] × 10^{10}g s^{-1} give account for the observational absorption in Lyα measured for the planetary system. Also, several models with anisotropic evaporation profiles for the planetary escaping atmosphere were carried out, showing that both, the escape through polar regions, resembling the emission associated with reconnection processes, and through the night side, produced by a strong stellar wind that compresses the planetary atmosphere and inhibits its escape from the day hemisphere yields larger absorptions than an isotropic planetary wind.

  17. Impact of sublimation losses in the mass balance of glaciers in semi-arid mountain regions

    NASA Astrophysics Data System (ADS)

    Ayala, Alvaro; Pellicciotti, Francesca; Burlando, Paolo; MacDonell, Shelley; McPhee, James

    2016-04-01

    Glaciers in semiarid mountain regions may lose an important part of their winter snow accumulation through sublimation processes that are enhanced by the high-elevation, intense radiation and dry atmosphere of these environments. As glaciers in these regions secure freshwater resources to lower valleys during summer and drought periods, it is important to advance in a detailed quantification of their sublimation losses. However, logistical concerns and complex meteorological features make the measuring and modelling of glacier mass balances a difficult task. In this study, we estimated the spring-summer mass balances of Tapado and Juncal Norte glaciers in the semiarid Andes of north-central Chile by running a distributed energy balance model that accounts for melt, refreezing and sublimation from the surface and blowing snow. Meteorological input data were available from on-glacier Automatic Weather Stations (AWS) that were installed during the ablation season of years 2005-06, 2008-09, 2013-14 and 2014-15. Snow pits, ablation stakes and a time-lapse camera that provided surface albedo were also available. Distributed air temperature and wind speed were dynamically downscaled from NASA MERRA reanalysis using the software WINDSIM and validated against the data from the AWSs. The rest of the meteorological variables were distributed using statistical relations with air temperature derived from the AWSs data. Initial snow conditions were estimated using satellite images and distributed manual snow depth measurements. Preliminary results show that total ablation diminishes with elevation and that, during the early ablation season (October-November), melt is the main ablation component below 4500 m with sublimation dominating the ablation above this elevation. Above 4500 m an important fraction of meltwater refreezes during night. As the ablation season advances (December-February), melt extends to higher elevations, refreezing plays a smaller role and sublimation is

  18. Measurement of the sizes of circumstellar dust shells around evolved stars with high mass loss rates

    NASA Technical Reports Server (NTRS)

    Phillips, T. G.; Knapp, G. R.

    1992-01-01

    The research supported by the NASA ADP contract NAG5-1153 has been completed. The attached paper, which will be submitted for publication in the Astrophysical Journal in January 1992, presents the results of this work. Here is a summary of the project and its results. A set of computer programs was developed to process the raw 60 micron and 100 micron IRAS survey data. The programs were designed to detect faint extended emission surrounding a bright unresolved source. Candidate objects were chosen from a list of red giant stars and young planetary nebulae which have been detected in millimeter/submillimeter lines of CO. Of the 279 stars examined, 55 were resolved at 60 microns. The principle results of the study are given. The average age for the shells surrounding the 9 Mira-type stars which are extended is 6 x 10(exp 4) yr. This suggests that the period during which these stars lose mass lasts for approx 10(exp 5) yr. The oldest shell found surrounds U Ori, and the youngest surrounds Mira itself. Some shells appear to be detached from the central star. This phenomenon is more common among older stars, suggesting that the mass loss becomes more episodic as the star sheds its envelope. Although all 8 stars less distant than 200 pc are resolved in the IRAS 60 micron data, 29 stars within 500 pc were not. These stars probably have younger circumstellar shells than those which were resolved. Almost all the carbon stars with distances of 500 pc or less have resolved shells, while only 1/2 of the oxygen-rich stars do. The resolved carbon star shells also are older on average than the oxygen-rich ones. These facts imply that carbon stars have been losing mass for a longer period, on average, than oxygen-rich red giants. Large circumstellar shells tend to be found at large distances from the galactic plane, confirming that the ISM density limits the size to which a dust shell can grow. Surprisingly, even very large shells seem to be nearly spherical, and do not appear to

  19. Dynamical Estimate of Post-main-sequence Stellar Masses in 47 Tucanae

    NASA Astrophysics Data System (ADS)

    Parada, Javiera; Richer, Harvey; Heyl, Jeremy; Kalirai, Jason; Goldsbury, Ryan

    2016-07-01

    We use the effects of mass segregation on the radial distribution of different stellar populations in the core of 47 Tucanae to find estimates for the masses of stars at different post-main-sequence evolutionary stages. We take samples of main-sequence (MS) stars from the core of 47 Tucanae, at different magnitudes (i.e., different masses), and use the effects of this dynamical process to develop a relation between the radial distance (RD) at which the cumulative distribution reaches the 20th and 50th percentile and stellar mass. From these relations we estimate the masses of different post-MS populations. We find that mass remains constant for stars going through the evolutionary stages from the upper MS up to the horizontal branch (HB). By comparing RDs of the HB stars with stars of lower masses, we can exclude a mass loss greater than 0.09 {M}ȯ during the red giant branch (RGB) stage at nearly the 3σ level. The slightly higher mass estimates for the asymptotic giant branch (AGB) are consistent with the AGB having evolved from somewhat more massive stars. The AGB also exhibits evidence of contamination by more massive stars, possibly blue straggler stars (BSSs), going through the RGB phase. We do not include the BSSs in this paper due to the complexity of these objects; instead, the complete analysis of this population is left for a companion paper. The process to estimate the masses described in this paper is exclusive to the core of 47 Tuc.

  20. Presolar Graphite from AGB Stars: Microstructure and s-Process Enrichment

    NASA Astrophysics Data System (ADS)

    Croat, Thomas K.; Stadermann, Frank J.; Bernatowicz, Thomas J.

    2005-10-01

    Correlated transmission electron microscopy and secondary ion mass spectrometry with submicron spatial resolution (NanoSIMS) investigations of the same presolar graphites spherules from the Murchison meteorite were conducted, to link the isotopic anomalies with the mineralogy and chemical composition of the graphite and its internal grains. Refractory carbide grains (especially titanium carbide) are commonly found within the graphite spherules, and most have significant concentrations of Zr, Mo, and Ru in solid solution, elements primarily produced by s-process nucleosynthesis. The effect of chemical fractionation on the Mo/Ti ratio in these carbides is limited, and therefore from this ratio one can infer the degree of s-process enrichment in the gas from which the graphite condensed. The resulting s-process enrichments within carbides are large (~200 times solar on average), showing that most of the carbide-containing graphites formed in the mass outflows of asymptotic giant branch (AGB) stars. NanoSIMS measurements of these graphites also show isotopically light carbon (mostly in the 100<12C/13C<400 range). The enrichment of these presolar graphites in both s-process elements and 12C considerably exceeds that astronomically observed around carbon stars. However, a natural correlation exists between 12C and s-process elements, as both form in the He intershell region of thermally pulsing AGB stars and are dredged up together to the surface. Their observation together suggests that these graphites may have formed in chemically and isotopically inhomogeneous regions around AGB stars, such as high-density knots or jets. As shown in the companion paper, a gas density exceeding that expected for smooth mass outflows is required for graphite of the observed size to condense at all in circumstellar environments, and the spatially inhomogeneous, high-density regions from which they condense may also be incompletely mixed with the surrounding gas. We have greatly expanded

  1. Optical Spectroscopy of the Post-AGB Star HD 89353

    NASA Astrophysics Data System (ADS)

    Mohamad-Yob, S.-J.; Gopir, G. K.; Malasan, H. L.; Anwar, R.

    2009-08-01

    Using the compact spectrograph at 600 lines/mm, and the 50.8 cm telescope at the Langkawi National Observatory, we obtained moderate resolution spectra of the post-AGB star HD 89353. The objective is to measure carbon and nitrogen abundances as a test of nucleosynthesis in AGB stars. The wavelength covered is between 4800-5600, 6467-7276, and 7035-7840 Å. A preliminary analysis showed the presence of the CI lines: 4932.00, 5039.05, 6586.269, 7108.934, 7111.480, 7113.178, 7115.182, 7116.991 and 7119.656 Å, and the NI lines: 7442.28 and 7423.63 Å. There was also emission line of H-alpha. We measured the equivalent widths of the C and N lines for future abundance calculation.

  2. Regional sea level change in response to ice mass loss in Greenland, the West Antarctic and Alaska

    NASA Astrophysics Data System (ADS)

    Brunnabend, S.-E.; Schröter, J.; Rietbroek, R.; Kusche, J.

    2015-11-01

    Besides the warming of the ocean, sea level is mainly rising due to land ice mass loss of the major ice sheets in Greenland, the West Antarctic, and the Alaskan Glaciers. However, it is not clear yet how these land ice mass losses influence regional sea level. Here, we use the global Finite Element Sea-ice Ocean Model (FESOM) to simulate sea surface height (SSH) changes caused by these ice mass losses and combine it with the passive ocean response to varying surface loading using the sea level equation. We prescribe rates of fresh water inflow, not only around Greenland, but also around the West Antarctic Ice Sheet and the mountain glaciers in Alaska with approximately present-day amplitudes of 200, 100, and 50 Gt/yr, respectively. Perturbations in sea level and in freshwater distribution with respect to a reference simulation are computed for each source separately and in their combination. The ocean mass change shows an almost globally uniform behavior. In the North Atlantic and Arctic Ocean, mass is redistributed toward coastal regions. Steric sea level change varies locally in the order of several centimeters on advective timescales of decades. Steric effects to local sea level differ significantly in different coastal locations, e.g., at North American coastal regions the steric effects may have the same order of magnitude as the mass driven effect, whereas at the European coast, steric effects remain small during the simulation period.

  3. Controls on mass loss and nitrogen dynamics of oak leaf litter along an urban-rural land-use gradient.

    PubMed

    Pouyat, Richard V; Carreiro, Margaret M

    2003-04-01

    Using reciprocal leaf litter transplants, we investigated the effects of contrasting environments (urban vs. rural) and intraspecific variations in oak leaf litter quality on mass loss rates and nitrogen (N) dynamics along an urban-rural gradient in the New York City metropolitan area. Differences in earthworm abundances and temperature had previously been documented in the stands along this gradient. Red oak leaf litter was collected and returned to its original source stand as native litter to measure decay rates along the gradient. To separate site effects from litter quality effects on decay, reciprocal transplants of litter were also made between stands at the extremes of the environmental gradient (urban and rural stands). Land-use had no effect on mass loss and N dynamics of native litter by the end of the 22-month incubation period. The lack of differences in native litter suggests the factors affecting decay were similar across the stands in this study. However, in the transplant study both environment and litter type strongly affected decay of oak leaf litter. On average urban and rural litter decomposed faster over the incubation period in urban than in rural stands (P=0.016 and P=0.001, respectively, repeated measures ANOVA). Differences in mass loss between urban and rural stands resulted in rural environments having less mass remaining than urban environments at the end of the incubation period (25.6 and 46.2% for urban and rural sites, respectively). Likewise, less N remained in leaf residue in urban sites (71.3%) compared to that in rural sites (115.1%). Litter type also affected mass loss rates during the 22-month incubation period. On average rural litter mass loss rates were faster than urban litter rates in both urban and rural stands (P=0.030 and P=0.026, respectively, repeated measures ANOVA). By the end of the incubation period, rural litter exhibited 43 and 20% greater mass loss and retained 44 and 5% less N than urban litter decomposing in

  4. The Case of the Missing Cyanogen-rich AGB Stars in Galactic Globular Clusters

    NASA Astrophysics Data System (ADS)

    Campbell, S. W.; Yong, D.; Wylie-de Boer, E. C.; Stancliffe, R. J.; Lattanzio, J. C.; Angelou, G. C.; Grundahl, F.; Sneden, C.

    2012-08-01

    The handful of available observations of AGB stars in Galactic Globular Clusters suggest that the GC AGB populations are dominated by cyanogen-weak stars (eg. Norris et al. 1981; Sneden et al. 2000). This contrasts strongly with the distributions on the RGB (and other) populations, which generally show a 50:50 bimodality in CN band strength. If this is a real difference then it presents a serious problem for low metallicity stellar evolution theory - since such a surface abundance change going from the RGB to AGB is not predicted by stellar models. However this is only a tentative conclusion, since it is based on very small AGB sample sizes. To test whether this problem really exists we have carried out an observational campaign targeting AGB stars in GCs. Our preliminary results indicate there is indeed a lack of CN-strong AGB stars.

  5. Clumpy dust clouds and extended atmosphere of the AGB star W Hydrae revealed with VLT/SPHERE-ZIMPOL and VLTI/AMBER

    NASA Astrophysics Data System (ADS)

    Ohnaka, K.; Weigelt, G.; Hofmann, K.-H.

    2016-05-01

    Context. Dust formation is thought to play an important role in the mass loss from stars at the asymptotic giant branch (AGB); however, where and how dust forms is still open to debate. Aims: We present visible polarimetric imaging observations of the well-studied AGB star W Hya taken with VLT/SPHERE-ZIMPOL as well as high spectral resolution long-baseline interferometric observations taken with the AMBER instrument at the Very Large Telescope Interferometer (VLTI). Our goal is to spatially resolve the dust and molecule formation region within a few stellar radii. Methods: We observed W Hya with VLT/SPHERE-ZIMPOL at three wavelengths in the continuum (645, 748, and 820 nm), in the Hα line at 656.3 nm, and in the TiO band at 717 nm. The VLTI/AMBER observations were carried out in the wavelength region of the CO first overtone lines near 2.3 μm with a spectral resolution of 12000. Results: Taking advantage of the polarimetric imaging capability of SPHERE-ZIMPOL combined with the superb adaptive optics performance, we succeeded in spatially resolving three clumpy dust clouds located at ~50 mas (~2 R⋆) from the central star, revealing dust formation very close to the star. The AMBER data in the individual CO lines suggest a molecular outer atmosphere extending to ~3 R⋆. Furthermore, the SPHERE-ZIMPOL image taken over the Hα line shows emission with a radius of up to ~160 mas (~7 R⋆). We found that dust, molecular gas, and Hα-emitting hot gas coexist within 2-3 R⋆. Our modeling suggests that the observed polarized intensity maps can reasonably be explained by large (0.4-0.5 μm) grains of Al2O3, Mg2SiO4, or MgSiO3 in an optically thin shell (τ550nm = 0.1 ± 0.02) with an inner and outer boundary radius of 1.9-2.0 R⋆ and 3 ± 0.5R⋆, respectively. The observed clumpy structure can be reproduced by a density enhancement of a factor of 4 ± 1. Conclusions: The grain size derived from our modeling of the SPHERE-ZIMPOL polarimetric images is consistent with

  6. Atmospheric mass loss from Hot Jupiters: chemical reactions and a new hypothesis for the origin of water in habitable planets

    NASA Astrophysics Data System (ADS)

    Pinotti, Rafael; Boechat-Roberty, Heloisa M.

    2015-08-01

    The chemistry along the mass loss of Hot Jupiters is generally considered to be simple, consisting mainly of atoms, prevented from forming more complex species by the intense radiation field from their host stars. However, the results of our chemical reaction simulations, involving 56 species and 566 reactions, indicate that many simple molecules, including H2O+ and OH+, are formed along the mass loss of HD 209458 b and analogs, in a region farther away from the planet, where the temperature is lower (T < 2000 K). Our simulations included benzene formation reactions; the results indicate that carbon chain species are not formed in the mass loss of HD 209458 b. We also formulate a new hypothesis for the origin of water on the surface of habitable planets in general: chemical interaction of their primordial atmospheres with hydrogen and oxygen ions from the atmospheric mass loss of primordial, low density Hot Jupiters. This mechanism could have possibly operated in the Solar System and accounted for the formation of the oceans of the Earth.

  7. e-MERLIN 21cm constraints on the mass-loss rates of OB stars in Cyg OB2

    NASA Astrophysics Data System (ADS)

    Morford, J. C.; Fenech, D. M.; Prinja, R. K.; Blomme, R.; Yates, J. A.

    2016-08-01

    We present e-MERLIN 21 cm (L-band) observations of single luminous OB stars in the Cygnus OB2 association, from the COBRaS Legacy programme. The radio observations potentially offer the most straightforward, least model-dependent, determinations of mass-loss rates, and can be used to help resolve current discrepancies in mass-loss rates via clumped and structured hot star winds. We report here that the 21 cm flux densities of O3 to O6 supergiant and giant stars are less than ˜ 70 μJy. These fluxes may be translated to `smooth' wind mass-loss upper limits of ˜ 4.4 - 4.8 × 10-6 M⊙ yr -1 for O3 supergiants and ≲ 2.9 × 10-6 M⊙ yr -1 for B0 to B1 supergiants. The first ever resolved 21 cm detections of the hypergiant (and LBV candidate) Cyg OB2 #12 are discussed; for multiple observations separated by 14 days, we detect a ˜ 69% increase in its flux density. Our constraints on the upper limits for the mass-loss rates of evolved OB stars in Cyg OB2 support the model that the inner wind region close to the stellar surface (where Hα forms) is more clumped than the very extended geometric region sampled by our radio observations.

  8. Heating from free-free absorption and the mass-loss rate of the progenitor stars to supernovae

    SciTech Connect

    Björnsson, C.-I.; Lundqvist, P. E-mail: peter@astro.su.se

    2014-06-01

    An accurate determination of the mass-loss rate of the progenitor stars to core-collapse supernovae is often limited by uncertainties pertaining to various model assumptions. It is shown that under conditions when the temperature of the circumstellar medium is set by heating due to free-free absorption, observations of the accompanying free-free optical depth allow a direct determination of the mass-loss rate from observed quantities in a rather model-independent way. The temperature is determined self-consistently, which results in a characteristic time dependence of the free-free optical depth. This can be used to distinguish free-free heating from other heating mechanisms. Since the importance of free-free heating is quite model dependent, this also makes possible several consistency checks of the deduced mass-loss rate. It is argued that the free-free absorption observed in SN 1993J is consistent with heating from free-free absorption. The deduced mass-loss rate of the progenitor star is, approximately, 10{sup –5} M {sub ☉} yr{sup –1} for a wind velocity of 10 km s{sup –1}.

  9. Greenland Ice Sheet Mass Loss and Outlet Glacier Dynamics from Laser Altimetry Record (1993-2013) (Invited)

    NASA Astrophysics Data System (ADS)

    Csatho, B. M.; Schenk, A. F.; Duncan, K.; Babonis, G. S.; Sonntag, J. G.; Krabill, W. B.; van den Broeke, M. R.; van Angelen, J.; Blair, J. B.; Hofton, M. A.

    2013-12-01

    Comprehensive monitoring of the Greenland Ice Sheet (GrIS) by satellite observations has revealed increasing mass loss since the late 1990s. Dynamic processes have been responsible for as much as half of this estimated loss, including ice flow adjustments to past climate variations and contemporary atmospheric and oceanic forcings. Dynamical processes act on different spatial and temporal scales and can cause non-linear changes, even on short, sub-decadal time scales. Quantitative investigation of these processes is imperative for improving ice sheet models and sea-level predictions. Our 1992-2011 altimetry record has shown that dynamic thinning substantially contributes to mass loss. The large spatial and temporal variations of dynamic mass loss and widespread intermittent thinning indicated the complexity of ice sheet response to climate forcing and points to the need of continuing monitoring of the GrIS at high spatial resolution. Airborne Topographic Mapper (ATM) and Laser Vegetation and Ice Sensor (LVIS) airborne laser altimetry measurements, acquired by NASA's IceBridge mission, allowed us to extend the altimetry record to 2013. We generated a record of ice thickness and mass change of the GrIS spanning the period of 1992-2013, reconstructed at several thousand locations using the Surface Elevation Reconstruction and Change detection (SERAC) approach. Elevation changes are corrected for Glacial Isostatic Adjustment and partitioned into climate and ice dynamics induced components. We present the evolution of ice dynamics and climate induced mass loss of the major GrIS drainage basins in 2003-2013 to investigate their contributions to sea-level change. The detailed record of outlet glacier elevation change is consistent with the propagation of dynamic thinning or thickening initiated at lower elevations. We focus our attention to SE and NE Greenland. In SE Greenland we investigate if thinning continued on fast flowing SE Greenland glaciers (e.g., Koge Bugt, A

  10. Macroclumping as solution of the discrepancy between Hα and P v mass loss diagnostics for O-type stars

    NASA Astrophysics Data System (ADS)

    Šurlan, B.; Hamann, W.-R.; Aret, A.; Kubát, J.; Oskinova, L. M.; Torres, A. F.

    2013-11-01

    Context. Recent studies of O-type stars have demonstrated that discrepant mass-loss rates are obtained when different diagnostic methods are employed. Fitting the unsaturated UV resonance lines (e.g., P v) gives drastically lower values than obtained from the Hα emission. Wind inhomogeneity (so-called "clumping") may be the main cause of this discrepancy. Aims: In a previous paper, we presented 3D Monte-Carlo calculations for the formation of scattering lines in a clumped stellar wind. In the present paper we select five O-type supergiants (from O4 to O7) and test whether the reported discrepancies can be resolved this way. Methods: In the first step, the analyses started with simulating the observed spectra with Potsdam Wolf-Rayet (PoWR) non-LTE model atmospheres. The mass-loss rates are adjusted to fit to the observed Hα emission lines best. For the unsaturated UV resonance lines (i.e., P v) we then applied our 3D Monte-Carlo code, which can account for wind clumps of any optical depths ("macroclumping"), a non-void interclump medium, and a velocity dispersion inside the clumps. The ionization stratifications and underlying photospheric spectra were adopted from the PoWR models. The properties of the wind clumps were constrained by fitting the observed resonance line profiles. Results: Our results show that with the mass-loss rates that fit Hα (and other Balmer and He ii lines), the UV resonance lines (especially the unsaturated doublet of P v) can also be reproduced with no problem when macroclumping is taken into account. There is no need to artificially reduce the mass-loss rates or to assume a subsolar phosphorus abundance or an extremely high clumping factor, unlike what was claimed by other authors. These consistent mass-loss rates are lower by a factor of 1.3 to 2.6, compared to the mass-loss rate recipe from Vink et al. Conclusions: Macroclumping resolves the previously reported discrepancy between Hα and P v mass-loss diagnostics. Based on

  11. WATER ICE IN HIGH MASS-LOSS RATE OH/IR STARS

    SciTech Connect

    Suh, Kyung-Won; Kwon, Young-Joo

    2013-01-10

    We investigate water-ice features in spectral energy distributions (SEDs) of high mass-loss rate OH/IR stars. We use a radiative transfer code which can consider multiple components of dust shells to make model calculations for various dust species including water ice in the OH/IR stars. We find that the model SEDs are sensitively dependent on the location of the water-ice dust shell. For two sample stars (OH 127.8+0.0 and OH 26.5+0.6), we compare the detailed model results with the infrared observational data including the spectral data from the Infrared Space Observatory (ISO). For the two sample stars, we reproduce the crystalline water-ice features (absorption at 3.1 {mu}m and 11.5 {mu}m; emission at 44 and 62 {mu}m) observed by ISO using a separate component of the water-ice dust shell that condensed at about 84-87 K (r {approx} 1500-1800 AU) as well as the silicate dust shell that condensed at about 1000 K (r {approx} 19-25 AU). For a sample of 1533 OH/IR stars, we present infrared two-color diagrams (2CDs) using the Infrared Astronomical Satellite and AKARI data compared with theoretical model results. We find that the theoretical models clearly show the effects of the crystalline water-ice features (absorption at 11.5 {mu}m and emission at 62 {mu}m) on the 2CDs.

  12. Towards a coherent view at infrared wavelengths of mass loss in Betelgeuse

    NASA Astrophysics Data System (ADS)

    Kervella, P.; Perrin, G.; Montargès, M.; Haubois, X.

    2013-05-01

    The violent convective motions, low surface gravity, and high brightness of red supergiants combine to trigger an intense stellar wind. As the distance from the star increases, the standard scenario is that the ejected material forms molecules, then dust particles. But this general picture is still fragmentary. Our goal is to assemble a better understanding of mass loss in Betelgeuse, considered as a prototype for its class, from its photosphere to the interface of its wind with the interstellar medium. Thanks to its proximity ( ≈ 197 pc), it is ideally suited for such a detailed study. Over the past few years, our team obtained an extensive set of observations of Betelgeuse from high angular resolution instruments, probing a broad range of spatial scales: 1) interferometric imaging of its photosphere and close envelope in the near- and thermal-IR domains (IOTA/IONIC), 2) adaptive optics "lucky imaging" of its compact molecular envelope (VLT/NACO, 1.0-2.2 μm), and 3) diffraction-limited imaging of its dusty envelope (VLT/VISIR, 8-20 μm). From our interferometric data, we detect the presence of spots at the surface of the star, as well as CO and H2O molecules, and dust particles close to the star. Within 6 R⋆, the flux distribution of the envelope is compatible with the presence of the CN molecule. At a few arcseconds from the central star, we observe a complex dusty envelope probably containing O-rich dust (e.g. silicates, alumina). We present an overview of these recent observational results and ongoing work. They provide new hints on the physical and chemical mechanisms through which Betelgeuse interacts with its environment.

  13. Heat shock protein 60 protects skeletal tissue against glucocorticoid-induced bone mass loss by regulating osteoblast survival.

    PubMed

    Wang, Feng-Sheng; Wu, Re-Wen; Ko, Jih-Yang; Tai, Ming-Hong; Ke, Huei-Ching; Yeh, Da-Wei; Wu, Shin-Long; Chen, Ming-Wen

    2011-11-01

    Excessive glucocorticoid administration accelerates osteoblast apoptosis and skeletal deterioration. Heat shock proteins (HSPs) regulate metabolic activities in osteoblastic cells. This study characterized the biological significance of HSP60 in glucocorticoid-induced bone loss. Rats were treated with glucocorticoid, HSP60 antisense oligonucleotides, or adenovirus-mediated HSP60 gene transfer. Bone mineral density, metaphyseal trabecular micro-architecture, and fragility were analyzed by dual X-ray absorptiometry, micro-computed tomography, and material testing, respectively. Differential proteomic profiles of bone tissue extracts were detected by bi-dimensional electrophoresis and mass spectrometry. Survival and proapoptotic signal transduction were quantified by immunoblotting. Glucocorticoid-treated rats had low bone mineral density and metaphyseal trabecular microstructure in association with downregulation of collagen 1α1 and HSP60 expressions in bone tissue. Gain of HSP60 function by adenovirus-mediated HSP60 gene transfer abrogated the deleterious effects of glucocorticoid treatment on bone mass, trabecular microstructure, and mechanical strength. Enhancement of HSP60 signaling attenuated the glucocorticoid-induced loss of trabecular bone volume, mineral acquisition reactions and osteoblast surface. HSP60 gene transfer activated ERK and Akt and reduced Bax and cytochrome c release, as well as caspase-3 cleavage, which attenuated the inhibitory effects of glucocorticoid treatment on osteoblast survival. Loss of HSP60 function by HSP60 antisense oligonucleotides accelerated mitochondrial apoptotic programs and osteoblast apoptosis. Knockdown of HSP60 induced loss of bone mass, micro-architecture integrity, and mechanical property. Taken together, loss of HSP60 signaling contributes to the glucocorticoid-induced enhancement of pro-apoptotic reactions, thereby accelerating osteoblast apoptosis and bone mass loss. Enhancement of HSP60 function is beneficial for

  14. Color-magnitude relations within globular cluster systems of giant elliptical galaxies: The effects of globular cluster mass loss and the stellar initial mass function

    SciTech Connect

    Goudfrooij, Paul; Kruijssen, J. M. Diederik E-mail: kruijssen@mpa-garching.mpg.de

    2014-01-01

    Several recent studies have provided evidence for a 'bottom-heavy' stellar initial mass function (IMF) in massive elliptical galaxies. Here we investigate the influence of the IMF shape on the recently discovered color-magnitude relation (CMR) among globular clusters (GCs) in such galaxies. To this end we use calculations of GC mass loss due to stellar and dynamical evolution to evaluate (1) the shapes of stellar mass functions in GCs after 12 Gyr of evolution as a function of current GC mass along with their effects on integrated-light colors and mass-to-light ratios, and (2) their impact on the effects of GC self-enrichment using the 2009 'reference' model of Bailin and Harris. As to the class of metal-poor GCs, we find the observed shape of the CMR (often referred to as the 'blue tilt') to be very well reproduced by Bailin and Harris's reference self-enrichment model once 12 Gyr of GC mass loss is taken into account. The influence of the IMF on this result is found to be insignificant. However, we find that the observed CMR among the class of metal-rich GCs (the 'red tilt') can only be adequately reproduced if the IMF was bottom-heavy (–3.0 ≲ α ≲ –2.3 in dN/dM∝M{sup α}), which causes the stellar mass function at subsolar masses to depend relatively strongly on GC mass. This constitutes additional evidence that the metal-rich stellar populations in giant elliptical galaxies were formed with a bottom-heavy IMF.

  15. Chemical weathering, mass loss, and dust inputs across a climate by time matrix in the Hawaiian Islands

    NASA Astrophysics Data System (ADS)

    Porder, Stephen; Hilley, George E.; Chadwick, Oliver A.

    2007-06-01

    We determined the total mass loss and rate of chemical weathering from three minimally eroded, Hawaiian lava flows that are ˜ 10, 170, and 350 ka old. Using a backhoe, we sampled the entire weathering zone at 28 sites and measured the depletion or enrichment of each major element in each soil horizon relative to parent material. We were able to assess the influence of both climate and substrate age on chemical weathering because each flow crosses a precipitation gradient from ˜ 600 to ˜ 2500 mm yr - 1 . Mass loss rates were highest for the 0-10 ka interval under the wettest climatic conditions (54 t km - 2 yr - 1 ), and decreased to near zero in the wet sites during the 10-170 and 170-350 ka intervals. Not surprisingly, weathering rates were lower in drier sites; ˜ 24 t km - 2 yr - 1 from 0-10 ka to < 2 t km - 2 yr - 1 thereafter. However the effects of precipitation were non-linear. There was a precipitation threshold below which mass loss was relatively small, and above which mass loss was substantial but insensitive to increased rainfall. Chemical weathering rates depend on tectonic uplift, erosion, climate, rock type or some combination thereof. By working on stable, uneroded surfaces of a single rock type across a well-constrained precipitation gradient, we were able to identify another potential driver: the rate of dust deposition. Although Hawaíi is one of the least dusty places in the northern hemisphere, dust inputs reached 82% of the total mass loss from the weathering zone at some sites, and averaged 30% on the 170 ka flow. This highlights the potential importance of dust as a component of observed weathering fluxes from catchments worldwide.

  16. Measured Mass-Loss Rates of Solar-like Stars as a Function of Age and Activity

    NASA Astrophysics Data System (ADS)

    Wood, Brian E.; Müller, Hans-Reinhard; Zank, Gary P.; Linsky, Jeffrey L.

    2002-07-01

    Collisions between the winds of solar-like stars and the local interstellar medium result in a population of hot hydrogen gas surrounding these stars. Absorption from this hot H I can be detected in high-resolution Lyα spectra of these stars from the Hubble Space Telescope. The amount of absorption can be used as a diagnostic for the stellar mass-loss rate. We present new mass-loss rate measurements derived in this fashion for four stars (ɛ Eri, 61 Cyg A, 36 Oph AB, and 40 Eri A). Combining these measurements with others, we study how mass loss varies with stellar activity. We find that for the solar-like GK dwarfs, the mass loss per unit surface area is correlated with X-ray surface flux. Fitting a power law to this relation yields M~F1.15+/-0.20X. The active M dwarf Proxima Cen and the very active RS CVn system λ And appear to be inconsistent with this relation. Since activity is known to decrease with age, the above power-law relation for solar-like stars suggests that mass loss decreases with time. We infer a power-law relation of M~t-2.00+/-0.52. This suggests that the solar wind may have been as much as 1000 times more massive in the distant past, which may have had important ramifications for the history of planetary atmospheres in our solar system, that of Mars in particular. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

  17. Spin-induced mass loss from rubble piles and the formation of asteroid satellites and pairs

    NASA Astrophysics Data System (ADS)

    Tanga, P.; Campo Bagatin, A.; Thirouin, A.; Cellino, A.; Comito, C.; Ortiz, J.; Richardson, D.; Hestroffer, D.

    2014-07-01

    Non-gravitational effects may change the angular momentum of asteroids up to a few tens of km in size to the point that rotational stability is lost at high spin rates. Once instability is initiated, mass loss may happen and potentially create satellites or dynamically detached components (pairs). We have studied this problem by means of numerical simulations and investigated the production of secondary objects of different sizes by direct splitting of the parent body under the assumption of a low internal angle of friction. We focused our attention on the effect of progressive spin-up of objects as a consequence of the YORP effect. Since asteroids are clearly not fluid but rocky bodies, one can assume that equilibrium theories --- also describing bifurcations (e.g., [1]) --- do not directly apply [2]. The equilibrium shapes of non-fluid bodies have been studied in the recent past by several authors, assuming that rubble-pile asteroids can be modeled as cohesionless granular systems in the frame of continuum theories [2--5]. [6] shows that a small amount of tensile strength could be sufficient for the survival of some fast rotators, even if they are internally fragmented. More relevant to this work are the results obtained by [7,8] by the same N-body approach that we use, i.e., by simulating the dynamics and the collisions of mono-dispersed hard spheres utilizing the PKDGRAV code [9,10]. The YORP effect is modeled by increasing rigid rotation by small increments with enough time to relax between subsequent spin-ups. In this work, our approach is based again on the same simulation code; however, our new exploration of the parameter space is broader than the previous study in the near-fluid regime, which is achieved by randomizing the initial particle positions somewhat to break the otherwise crystalline structure of monodisperse particle packing. We find that the transformation of objects into prolate ellipsoids is an efficient process when the internal angle of

  18. Understanding AGB evolution in Galactic bulge stars from high-resolution infrared spectroscopy

    NASA Astrophysics Data System (ADS)

    Uttenthaler, S.; Blommaert, J. A. D. L.; Wood, P. R.; Lebzelter, T.; Aringer, B.; Schultheis, M.; Ryde, N.

    2015-08-01

    An analysis of high-resolution near-infrared spectra of a sample of 45 asymptotic giant branch (AGB) stars towards the Galactic bulge is presented. The sample consists of two subsamples, a larger one in the inner and intermediate bulge, and a smaller one in the outer bulge. The data are analysed with the help of hydrostatic model atmospheres and spectral synthesis. We derive the radial velocity of all stars, and the atmospheric chemical mix ([Fe/H], C/O, 12C/13C, Al, Si, Ti, and Y) where possible. Our ability to model the spectra is mainly limited by the (in)completeness of atomic and molecular line lists, at least for temperatures down to Teff ≈ 3100 K. We find that the subsample in the inner and intermediate bulge is quite homogeneous, with a slightly subsolar mean metallicity and only few stars with supersolar metallicity, in agreement with previous studies of non-variable M-type giants in the bulge. All sample stars are oxygen-rich, C/O < 1.0. The C/O and carbon isotopic ratios suggest that third dredge-up (3DUP) is absent among the sample stars, except for two stars in the outer bulge that are known to contain technetium. These stars are also more metal-poor than the stars in the intermediate or inner bulge. Current stellar masses are determined from linear pulsation models. The masses, metallicities and 3DUP behaviour are compared to AGB evolutionary models. We conclude that these models are partly in conflict with our observations. Furthermore, we conclude that the stars in the inner and intermediate bulge belong to a more metal-rich population that follows bar-like kinematics, whereas the stars in the outer bulge belong to the metal-poor, spheroidal bulge population.

  19. Effects of the LBV Primary's Mass-loss Rate on the 3D Hydrodynamics of eta Carinae's Colliding Winds

    NASA Technical Reports Server (NTRS)

    Madura, Thomas I.; Gull, Theodore R.; Cocoran, M.; Okazaki, A.; Owocki, S.; Russell, C.; Hamaguchi, K.; Clementel, N; Groh, J.; Hillier, D. J.

    2013-01-01

    At the heart of eta Carinae's spectacular "Homunculus" nebula lies an extremely luminous (L(sub Total) greater than approximately 5 × 10(exp 6) solar luminosity) colliding wind binary with a highly eccentric (e approximately 0.9), 5.54-year orbit (Figure 1). The primary of the system, a Luminous Blue Variable (LBV), is our closest (D approximately 2.3 kpc) and best example of a pre-hypernova or pre-gamma ray burst environment. The remarkably consistent and periodic RXTE X-ray light curve surprisingly showed a major change during the system's last periastron in 2009, with the X-ray minimum being approximately 50% shorter than the minima of the previous two cycles1. Between 1998 and 2011, the strengths of various broad stellar wind emission lines (e.g. Halpha, Fe II) in line-of-sight (l.o.s.) also decreased by factors of 1.5 - 3 relative to the continuum2. The current interpretation for these changes is that they are due to a gradual factor of 2 - 4 drop in the primary's mass-loss rate over the last approximately 15 years1, 2. However, while a secular change is seen for a direct view of the central source, little to no change is seen in profiles at high stellar latitudes or reflected off of the dense, circumbinary material known as the "Weigelt blobs"2, 3. Moreover, model spectra generated with CMFGEN predict that a factor of 2 - 4 drop in the primary's mass-loss rate should lead to huge changes in the observed spectrum, which thus far have not been seen. Here we present results from large- (plus or minus 1620 AU) and small- (plus or minus 162 AU) domain, full 3D smoothed particle hydrodynamics (SPH) simulations of eta Car's massive binary colliding winds for three different primary-star mass-loss rates (2.4, 4.8, and 8.5 × 10(exp -4) solar mass/yr). The goal is to investigate how the mass-loss rate affects the 3D geometry and dynamics of eta Car's optically-thick wind and spatially-extended wind-wind collision (WWC) regions, both of which are known sources of

  20. Short-term variability and mass loss in Be stars. I. BRITE satellite photometry of η and μ Centauri

    NASA Astrophysics Data System (ADS)

    Baade, D.; Rivinius, Th.; Pigulski, A.; Carciofi, A. C.; Martayan, Ch.; Moffat, A. F. J.; Wade, G. A.; Weiss, W. W.; Grunhut, J.; Handler, G.; Kuschnig, R.; Mehner, A.; Pablo, H.; Popowicz, A.; Rucinski, S.; Whittaker, G.

    2016-04-01

    Context. Empirical evidence for the involvement of nonradial pulsations (NRPs) in the mass loss from Be stars ranges from (i) a singular case (μ Cen) of repetitive mass ejections triggered by multi-mode beating to (ii) several photometric reports about enormous numbers of pulsation modes that suddenly appear during outbursts and on to (iii) effective single-mode pulsators. Aims: The purpose of this study is to develop a more detailed empirical description of the star-to-disk mass transfer and to check the hypothesis that spates of transient nonradial pulsation modes accompany and even drive mass-loss episodes. Methods: The BRITE Constellation of nanosatellites was used to obtain mmag photometry of the Be stars η and μ Cen. Results: In the low-inclination star μ Cen, light pollution by variable amounts of near-stellar matter prevented any new insights into the variability and other properties of the central star. In the equator-on star η Cen, BRITE photometry and Heros echelle spectroscopy from the 1990s reveal an intricate clockwork of star-disk interactions. The mass transfer is modulated with the frequency difference of two NRP modes and an amplitude three times as large as the amplitude sum of the two NRP modes. This process feeds a high-amplitude circumstellar activity running with the incoherent and slightly lower so-called Štefl frequency. The mass-loss-modulation cycles are tightly coupled to variations in the value of the Štefl frequency and in its amplitude, albeit with strongly drifting phase differences. Conclusions: The observations are well described by the decomposition of the mass loss into a pulsation-related engine in the star and a viscosity-dominated engine in the circumstellar disk. Arguments are developed that large-scale gas-circulation flows occur at the interface. The propagation rates of these eddies manifest themselves as Štefl frequencies. Bursts in power spectra during mass-loss events can be understood as the noise inherent to

  1. Water quality and nitrogen mass loss from anaerobic lagoon columns receiving pretreated influent

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Control methods are needed to abate ammonia losses from swine anaerobic lagoons to reduce contribution of confined swine operations to air pollution. In a 15-month meso-scale column study, we evaluated the effect of manure pretreatment on water quality, reduction of N losses, and sludge accumulation...

  2. Gas Phase Chemistry of Li+ with Amides: the Observation of LiOH Loss in Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Guo, Cheng; Zhou, Yuping; Liu, Pengyuan; Chai, Yunfeng; Pan, Yuanjiang

    2012-07-01

    Collision-induced dissociation (CID) of Li+ adducts of three sets of compounds that contains an amide bond, including 2-(4, 6-dimethoxypyrimidin-2-ylsulfanyl)- N-phenylbenzamide, its derivatives and simpler structures was investigated by electrospray ionization tandem mass spectrometry (ESI-MS/MS). Observed fragment ions include those that reflect loss of LiOH. Other product ions result from the Smiles rearrangement and direct C-S bond cleavage. MS/MS of H/D exchange products demonstrated occurrence of a 1,3-H shift from the amide nitrogen atom to the phenyl ring of these compounds. The LiOH loss from Li+ adducts of amides was further examined by CID of [M + Li]+ ions of N-phenylbenzamide and N-phenylcinnamide. Loss of LiOH was essentially the sole fragmentation reaction observed for the former. For the latter, both losses of LiOH and H2O were discovered. The presence of electron-donating substituents of the phenyl ring of these compounds was found to facilitate elimination of LiOH, while that loss was retarded by electron-withdrawing substituents. Proposed fragment ion structures were supported by elemental compositions deduced from ultrahigh resolution Fourier transform ion cyclotron resonance tandem mass spectrometry (FTICR-MS/MS) m/z value determinations. Density functional theory-based (DFT) calculations were performed to evaluate potential mechanisms for these reactions.

  3. Increased Consumption of Dairy Foods and Protein during Diet- and Exercise-Induced Weight Loss Promotes Fat Mass Loss and Lean Mass Gain in Overweight and Obese Premenopausal Women1234

    PubMed Central

    Josse, Andrea R.; Atkinson, Stephanie A.; Tarnopolsky, Mark A.; Phillips, Stuart M.

    2011-01-01

    Weight loss can have substantial health benefits for overweight or obese persons; however, the ratio of fat:lean tissue loss may be more important. We aimed to determine how daily exercise (resistance and/or aerobic) and a hypoenergetic diet varying in protein and calcium content from dairy foods would affect the composition of weight lost in otherwise healthy, premenopausal, overweight, and obese women. Ninety participants were randomized to 3 groups (n = 30/group): high protein, high dairy (HPHD), adequate protein, medium dairy (APMD), and adequate protein, low dairy (APLD) differing in the quantity of total dietary protein and dairy food-source protein consumed: 30 and 15%, 15 and 7.5%, or 15 and <2% of energy, respectively. Body composition was measured by DXA at 0, 8, and 16 wk and MRI (n = 39) to assess visceral adipose tissue (VAT) volume at 0 and 16 wk. All groups lost body weight (P < 0.05) and fat (P < 0.01); however, fat loss during wk 8–16 was greater in the HPHD group than in the APMD and APLD groups (P < 0.05). The HPHD group gained lean tissue with a greater increase during 8–16 wk than the APMD group, which maintained lean mass and the APLD group, which lost lean mass (P < 0.05). The HPHD group also lost more VAT as assessed by MRI (P < 0.05) and trunk fat as assessed by DXA (P < 0.005) than the APLD group. The reduction in VAT in all groups was correlated with intakes of calcium (r = 0.40; P < 0.05) and protein (r = 0.32; P < 0.05). Therefore, diet- and exercise-induced weight loss with higher protein and increased dairy product intakes promotes more favorable body composition changes in women characterized by greater total and visceral fat loss and lean mass gain. PMID:21775530

  4. EUV-driven mass-loss of protoplanetary cores with hydrogen-dominated atmospheres: the influences of ionization and orbital distance

    NASA Astrophysics Data System (ADS)

    Erkaev, N. V.; Lammer, H.; Odert, P.; Kislyakova, K. G.; Johnstone, C. P.; Güdel, M.; Khodachenko, M. L.

    2016-08-01

    We investigate the loss rates of the hydrogen atmospheres of terrestrial planets with a range of masses and orbital distances by assuming a stellar extreme ultraviolet (EUV) luminosity that is 100 times stronger than that of the current Sun. We apply a 1D upper atmosphere radiation absorption and hydrodynamic escape model that takes into account ionization, dissociation and recombination to calculate hydrogen mass-loss rates. We study the effects of the ionization, dissociation and recombination on the thermal mass-loss rates of hydrogen-dominated super-Earths and compare the results to those obtained by the energy-limited escape formula which is widely used for mass-loss evolution studies. Our results indicate that the energy-limited formula can to a great extent over- or underestimate the hydrogen mass-loss rates by amounts that depend on the stellar EUV flux and planetary parameters such as mass, size, effective temperature and EUV absorption radius.

  5. Weight loss may be a better approach for managing musculoskeletal conditions than increasing muscle mass and strength

    PubMed Central

    Kim, Bokun; Tsujimoto, Takehiko; So, Rina; Zhao, Xiaoguang; Suzuki, Shun; Kim, Taeho; Tanaka, Kiyoji

    2015-01-01

    To prevent or remedy musculoskeletal conditions, the relationship between obesity and the characteristics of muscle mass and strength need to be clarified. [Subjects and Methods] A total of 259 Japanese males aged 30–64 years were classified into 4 groups according to the Japanese obesity criteria. Body composition was evaluated, and handgrip strength and knee extensor strength were measured for the upper and lower extremities, respectively. Physical performance was evaluated with a jump test. [Results] Obesity was positively correlated with skeletal muscle mass index, percentage of whole-body fat, and leg muscle strength and negatively correlated with the percentage of muscle mass index, body weight-normalized handgrip strength, and knee extensor strength, and the jump test results. [Conclusion] Weight loss may be a better approach than increasing muscle mass and strength to improve musculoskeletal conditions in obese adult males. PMID:26834353

  6. Hydrodynamic simulations of the interaction between an AGB star and a main-sequence companion in eccentric orbits

    NASA Astrophysics Data System (ADS)

    Staff, Jan E.; De Marco, Orsola; Macdonald, Daniel; Galaviz, Pablo; Passy, Jean-Claude; Iaconi, Roberto; Low, Mordecai-Mark Mac

    2016-02-01

    The Rotten Egg Nebula has at its core a binary composed of a Mira star and an A-type companion at a separation >10 au. It has been hypothesized to have formed by strong binary interactions between the Mira and a companion in an eccentric orbit during periastron passage ˜800 yr ago. We have performed hydrodynamic simulations of an asymptotic giant branch (AGB) star interacting with companions with a range of masses in orbits with a range of initial eccentricities and periastron separations. For reasonable values of the eccentricity, we find that Roche lobe overflow can take place only if the periods are ≪100 yr. Moreover, mass transfer causes the system to enter a common envelope phase within several orbits. Since the central star of the Rotten Egg nebula is an AGB star, we conclude that such a common envelope phase must have lead to a merger, so the observed companion must have been a tertiary companion of a binary that merged at the time of nebula ejection. Based on the mass and time-scale of the simulated disc formed around the companion before the common envelope phase, we analytically estimate the properties of jets that could be launched. Allowing for super-Eddington accretion rates, we find that jets similar to those observed are plausible, provided that the putative lost companion was relatively massive.

  7. Nonradial instability strips for post-AGB stars

    SciTech Connect

    Stanghellini, L. ); Cox, A.N. ); Starrfield, S.G. . Dept. of Physics and Astronomy Los Alamos National Lab., NM )

    1990-01-01

    We test several pre-degenerate (PNN and DO) and degenerate (DB) models for stability against nonradial oscillations. These models lie on the 0.6 M{sub {circle dot}} evolutionary track calculated by Iben. The post-AGB stars have a residual CO core with only a little surface hydrogen and helium. In order to match all the observed pulsators. We use three different surface compositions for the DO stars, and a pure helium surface for the DB white dwarfs. We find 3 DO and 1 DB instability strips that we compare to the available observations. 16 refs., 1 fig.

  8. Mass loss in HR 1040 /A0 Ia/ - Analysis of Mg II lambda 2802 and H-alpha

    NASA Technical Reports Server (NTRS)

    Kunasz, P. B.; Morrison, N. D.; Spressart, B.

    1983-01-01

    It is pointed out that International Ultraviolet Explorer (IUE) data for several early A type supergiants are now available to complement the ground-based spectroscopic data available for these bright stars. An examination of the resonance doublet of Mg II in the A type supergiants reveals that HR 1040 (HD 21389) is the only star in the observational literature in which a violet-shifted, deep absorption line is present without complete saturation. From an unsaturated profile, a good estimate of Mg(+) density can be found by means of accurate radiative transfer calculations. A relation can then be derived between mass loss rate and ionization balance. When certain velocity-related quantities can be estimated from a Mg II line profile, the H-alpha provides an estimate of the mass loss rate. The present investigation is concerned with an application of these diagnostics to HR 1040.

  9. What Is, Or Should Be, The AGB? A Report from the Membership.

    ERIC Educational Resources Information Center

    Davis, Junius A.; And Others

    This document presents the results of a survey of member presidents and trustees of the Association of Governing Boards (AGB). The questionnaire employed several strategies for determining member needs and interests, and their perception of the role that the AGB should play in serving those needs and interests. First, a number of frequent concerns…

  10. Recent accelerating mass loss of southeast Tibetan glaciers and the relationship with changes in macroscale atmospheric circulations

    NASA Astrophysics Data System (ADS)

    Yang, Wei; Guo, Xiaofeng; Yao, Tandong; Zhu, Meilin; Wang, Yongjie

    2016-08-01

    The mass balance history (1980-2010) of a monsoon-dominated glacier in the southeast Tibetan Plateau is reconstructed using an energy balance model and later interpreted with regard to macroscale atmospheric variables. The results show that this glacier is characterized by significant interannual mass fluctuations over the past three decades, with a remarkably high mass loss during the recent period of 2003-2010. Analysis of the relationships between glacier mass balance and climatic variables shows that interannual temperature variability in the monsoonal season (June-September) is a primary driver of its mass balance fluctuations, but monsoonal precipitation tends to play an accentuated role for driving the observed glacier mass changes due to their covariation (concurrence of warm/dry and cold/wet climates) in the monsoon-influenced southeast Tibetan Plateau. Analysis of the atmospheric circulation pattern reveals that the predominance of anticyclonic/cyclonic circulations prevailing in the southeastern/northern Tibetan Plateau during 2003-2010 contributes to increased air temperature and decreased precipitation in the southeast Tibetan Plateau. Regionally contrasting atmospheric circulations explain the distinct mass changes between in the monsoon-influenced southeast Tibetan Plateau and in the north Tibetan Plateau/Tien Shan Mountains during 2003-2010. The macroscale climate change seems to be linked with the Europe-Asia teleconnection.

  11. Characterizing AGB stars in Wide-field Infrared Survey Explorer (WISE) bands

    NASA Astrophysics Data System (ADS)

    Lian, Jianhui; Zhu, Qingfeng; Kong, Xu; He, Jinhua

    2014-04-01

    Aims: Since asymptotic giant branch (AGB) stars are bright and extended infrared objects, most Galactic AGB stars saturate the Wide-field Infrared Survey Explorer (WISE) detectors and therefore the WISE magnitudes that are restored by applying point-spread-function fitting need to be verified. Statistical properties of circumstellar envelopes around AGB stars are discussed on the basis of a WISE AGB catalog verified in this way. Methods: We cross-matched an AGB star sample with the WISE All-Sky Source Catalog and the Two Mircon All Sky Survey catalog. Infrared Space Observatory (ISO) spectra of a subsample of WISE AGB stars were also exploited. The dust radiation transfer code DUSTY was used to help predict the magnitudes in the W1 and W2 bands, the two WISE bands most affected by saturation, for calibration purpose, and to provide physical parameters of the AGB sample stars for analysis. Results: DUSTY is verified against the ISO spectra to be a good tool to reproduce the spectral energy distributions of these AGB stars. Systematic magnitude-dependent offsets have been identified in WISE W1 and W2 magnitudes of the saturated AGB stars, and empirical calibration formulas are obtained for them on the basis of 1877 (W1) and 1558 (W2) AGB stars that are successfully fit with DUSTY. According to the calibration formulas, the corrections for W1 at 5 mag and W2 at 4 mag are -0.383 and 0.217 mag, respectively. In total, we calibrated the W1/W2 magnitudes of 2390/2021 AGB stars. The model parameters from the DUSTY and the calibrated WISE W1 and W2 magnitudes are used to discuss the behavior of the WISE color-color diagrams of AGB stars. The model parameters also reveal that O-rich AGB stars with opaque circumstellar envelopes are much rarer than opaque C-rich AGB stars toward the anti-Galactic center direction, which we attribute to the metallicity gradient of our Galaxy. The synthetic photometry and input parameters for the model grid are only available at the CDS via

  12. FUNDAMENTAL PARAMETERS, INTEGRATED RED GIANT BRANCH MASS LOSS, AND DUST PRODUCTION IN THE GALACTIC GLOBULAR CLUSTER 47 TUCANAE

    SciTech Connect

    McDonald, I.; Zijlstra, A. A.; Boyer, M. L.; Gordon, K.; Meixner, M.; Sewilo, M.; Shiao, B.; Whitney, B.; Van Loon, J. Th.; Hora, J. L.; Robitaille, T.; Babler, B.; Meade, M.; Block, M.; Misselt, K.

    2011-04-01

    Fundamental parameters and time evolution of mass loss are investigated for post-main-sequence stars in the Galactic globular cluster 47 Tucanae (NGC 104). This is accomplished by fitting spectral energy distributions (SEDs) to existing optical and infrared photometry and spectroscopy, to produce a true Hertzsprung-Russell diagram. We confirm the cluster's distance as d = 4611{sup +213}{sub -200} pc and age as 12 {+-} 1 Gyr. Horizontal branch models appear to confirm that no more red giant branch mass loss occurs in 47 Tuc than in the more metal-poor {omega} Centauri, though difficulties arise due to inconsistencies between the models. Using our SEDs, we identify those stars that exhibit infrared excess, finding excess only among the brightest giants: dusty mass loss begins at a luminosity of {approx}1000 L{sub sun}, becoming ubiquitous above L = 2000 L{sub sun}. Recent claims of dust production around lower-luminosity giants cannot be reproduced, despite using the same archival Spitzer imagery.

  13. The X-Ray Lightcurve of Eta Carinae: Refinement of the Orbit and Evidence for Phase Dependent Mass Loss

    NASA Technical Reports Server (NTRS)

    Corcoran, M. F.; Ishibashi, K.; Swank, J. H.; Petre, R.; White, Nicholas E. (Technical Monitor)

    2000-01-01

    We solve the RXTE X-ray lightcurve of the extremely luminous and massive star eta Carinae with a colliding wind emission model to refine the ground-based orbital elements. The sharp decline to X-ray minimum at the end of 1997 fixes the date of the last periastron passage at 1997.95 +/- 0.05, not 1998.13 as derived from ground-based radial velocities. This helps resolve a discrepancy between the ground-based radial velocities and spatially-resolved velocity measures obtained by STIS. The X-ray data are consistent with a mass function f(M) approx. = 1.5, lower than the value f(M) approx. = 7.5 previously reported, so that the masses of eta Carinae and the companion are M(sub eta) greater than or = 80 solar mass and M(sub c) approx. 30 solar mass respectively. In addition the X-ray data suggest that the mass loss rate from eta Carinae is generally less than 3 x 10(exp -4) solar mass/yr, about a factor of 5 lower than that derived from some observations in other wavebands. We could not match the duration of the X-ray minimum with any standard colliding wind model in which the wind is spherically symmetric and the mass loss rate is constant. However we show that we can match the variations around X-ray minimum if we include an increase of a factor of approx. 20 in the mass loss rate from eta Carinae for approximately 80 days following periastron. If real, this excess in M would be the first evidence of enhanced mass flow off the primary when the two stars are close (presumably driven by tidal interactions). Our interpretation of the X-ray data suggest that the ASCA and RXTE X-ray spectra near the X-ray minimum are significantly contaminated by unresolved hard emission (E greater than or = 2 keV) from sonic other nearby source, probably associated with scattering of tile colliding wind emission by circumstellar dust. Based on the X-ray fluxes the distance to n Carinae is 2300 pc with formal uncertainties of only approx. 10%.

  14. Out on a Limb: Updates on the Search for X-ray Emission from AGB Stars

    NASA Astrophysics Data System (ADS)

    Montez, Rodolfo; Ramstedt, Sofia; Santiago-Boyd, Andrea; Kastner, Joel; Vlemmings, Wouter

    2016-01-01

    X-rays from asymptotic giant branch (AGB) stars are rarely detected, however, few modern X-ray observatories have targeted AGB stars. In 2012, we searched a list of 480 galactic AGB stars and found a total of 13 targeted or serendipitous observations with few detections (Ramstedt et al. 2012). Since this initial search new programs have successfully targeted and detected X-ray emission from a handful of AGB stars. The X-ray emission, when detected, reveals high temperature plasma (>= 10 MK). This plasma might be heated by a large-scale magnetic field or indicate the presence of accretion onto a compact companion. In this poster, we update our search for X-ray emission from AGB stars with a review of their characteristics, potential origins, and impact of X-ray emission in this late stage of stellar evolution.

  15. Rapid body mass loss affects erythropoiesis and hemolysis but does not impair aerobic performance in combat athletes.

    PubMed

    Reljic, D; Feist, J; Jost, J; Kieser, M; Friedmann-Bette, B

    2016-05-01

    Rapid body mass loss (RBML) before competition was found to decrease hemoglobin mass (Hbmass ) in elite boxers. This study aimed to investigate the underlying mechanisms of this observation. Fourteen well-trained combat athletes who reduced body mass before competitions (weight loss group, WLG) and 14 combat athletes who did not practice RBML (control group, CON) were tested during an ordinary training period (t-1), 1-2 days before an official competition (after 5-7 days RBML in WLG, t-2), and after a post-competition period (t-3). In WLG, body mass (-5.5%, range: 2.9-6.8 kg) and Hbmass (-4.1%) were significantly (P < 0.001) reduced after RBML and were still decreased by 1.6% (P < 0.05) and 2.6% (P < 0.001) at t-3 compared with t-1. After RBML, erythropoietin, reticulocytes, haptoglobin, triiodothyronine (FT3 ), and free androgen index (FAI) were decreased compared with t-1 and t-3. An increase occurred in ferritin and bilirubin. Peak treadmill-running performance and VO2peak did not change significantly, but performance at 4-mmol lactate threshold was higher after RBML (P < 0.05). In CON, no significant changes were found in any parameter. Apparently, the significant decrease in Hbmass after RBML in combat athletes was caused by impaired erythropoiesis and increased hemolysis without significant impact on aerobic performance capacity. PMID:25916419

  16. Comprehensive quantification of triacylglycerols in soybean seeds by electrospray ionization mass spectrometry with multiple neutral loss scans

    DOE PAGESBeta

    Li, Maoyin; Butka, Emily; Wang, Xuemin

    2014-10-10

    Soybean seeds are an important source of vegetable oil and biomaterials. The content of individual triacylglycerol species (TAG) in soybean seeds is difficult to quantify in an accurate and rapid way. The present study establishes an approach to quantify TAG species in soybean seeds utilizing an electrospray ionization tandem mass spectrometry with multiple neutral loss scans. Ten neutral loss scans were performed to detect the fatty acyl chains of TAG, including palmitic (P, 1650), linolenic (Ln, 1853), linoleic (L, 1852), oleic (O, 1851), stearic (S, 1850), eicosadienoic (2052), gadoleic (2051), arachidic (2050), erucic (2251), and behenic (2250). The abundance ofmore » ten fatty acyl chains at 46 TAG masses (mass-to-charge ratio, m/z) were determined after isotopic deconvolution and correction by adjustment factors at each TAG mass. The direct sample infusion and multiple internal standards correction allowed a rapid and accurate quantification of TAG species. Ninety-three TAG species were resolved and their levels were determined.The most abundant TAG species were LLL, OLL, LLLn, PLL, OLLn, OOL, POL, and SLL. Many new species were detected and quantified. As a result, this shotgun lipidomics approach should facilitate the study of TAG metabolism and genetic breeding of soybean seeds for desirable TAG content and composition.« less

  17. Comprehensive quantification of triacylglycerols in soybean seeds by electrospray ionization mass spectrometry with multiple neutral loss scans

    SciTech Connect

    Li, Maoyin; Butka, Emily; Wang, Xuemin

    2014-10-10

    Soybean seeds are an important source of vegetable oil and biomaterials. The content of individual triacylglycerol species (TAG) in soybean seeds is difficult to quantify in an accurate and rapid way. The present study establishes an approach to quantify TAG species in soybean seeds utilizing an electrospray ionization tandem mass spectrometry with multiple neutral loss scans. Ten neutral loss scans were performed to detect the fatty acyl chains of TAG, including palmitic (P, 1650), linolenic (Ln, 1853), linoleic (L, 1852), oleic (O, 1851), stearic (S, 1850), eicosadienoic (2052), gadoleic (2051), arachidic (2050), erucic (2251), and behenic (2250). The abundance of ten fatty acyl chains at 46 TAG masses (mass-to-charge ratio, m/z) were determined after isotopic deconvolution and correction by adjustment factors at each TAG mass. The direct sample infusion and multiple internal standards correction allowed a rapid and accurate quantification of TAG species. Ninety-three TAG species were resolved and their levels were determined.The most abundant TAG species were LLL, OLL, LLLn, PLL, OLLn, OOL, POL, and SLL. Many new species were detected and quantified. As a result, this shotgun lipidomics approach should facilitate the study of TAG metabolism and genetic breeding of soybean seeds for desirable TAG content and composition.

  18. Comprehensive Quantification of Triacylglycerols in Soybean Seeds by Electrospray Ionization Mass Spectrometry with Multiple Neutral Loss Scans

    PubMed Central

    Li, Maoyin; Butka, Emily; Wang, Xuemin

    2014-01-01

    Soybean seeds are an important source of vegetable oil and biomaterials. The content of individual triacylglycerol species (TAG) in soybean seeds is difficult to quantify in an accurate and rapid way. The present study establishes an approach to quantify TAG species in soybean seeds utilizing an electrospray ionization tandem mass spectrometry with multiple neutral loss scans. Ten neutral loss scans were performed to detect the fatty acyl chains of TAG, including palmitic (P, 16:0), linolenic (Ln, 18:3), linoleic (L, 18:2), oleic (O, 18:1), stearic (S, 18:0), eicosadienoic (20:2), gadoleic (20:1), arachidic (20:0), erucic (22:1), and behenic (22:0). The abundance of ten fatty acyl chains at 46 TAG masses (mass-to-charge ratio, m/z) were determined after isotopic deconvolution and correction by adjustment factors at each TAG mass. The direct sample infusion and multiple internal standards correction allowed a rapid and accurate quantification of TAG species. Ninety-three TAG species were resolved and their levels were determined. The most abundant TAG species were LLL, OLL, LLLn, PLL, OLLn, OOL, POL, and SLL. Many new species were detected and quantified. This shotgun lipidomics approach should facilitate the study of TAG metabolism and genetic breeding of soybean seeds for desirable TAG content and composition. PMID:25301200

  19. Constraints on continental crustal mass loss via chemical weathering using lithium and its isotopes

    PubMed Central

    Liu, Xiao-Ming; Rudnick, Roberta L.

    2011-01-01

    Chemical weathering, as well as physical erosion, changes the composition and shapes the surface of the continental crust. However, the amount of continental material that has been lost over Earth’s history due to chemical weathering is poorly constrained. Using a mass balance model for lithium inputs and outputs from the continental crust, we find that the mass of continental crust that has been lost due to chemical weathering is at least 15% of the original mass of the juvenile continental crust, and may be as high as 60%, with a best estimate of approximately 45%. Our results suggest that chemical weathering and subsequent subduction of soluble elements have major impacts on both the mass and the compositional evolution of the continental crust. PMID:22184221

  20. Constraints on continental crustal mass loss via chemical weathering using lithium and its isotopes.

    PubMed

    Liu, Xiao-Ming; Rudnick, Roberta L

    2011-12-27

    Chemical weathering, as well as physical erosion, changes the composition and shapes the surface of the continental crust. However, the amount of continental material that has been lost over Earth's history due to chemical weathering is poorly constrained. Using a mass balance model for lithium inputs and outputs from the continental crust, we find that the mass of continental crust that has been lost due to chemical weathering is at least 15% of the original mass of the juvenile continental crust, and may be as high as 60%, with a best estimate of approximately 45%. Our results suggest that chemical weathering and subsequent subduction of soluble elements have major impacts on both the mass and the compositional evolution of the continental crust. PMID:22184221

  1. Sleeve Gastrectomy Induces Loss of Weight and Fat Mass in Obese Rats, but Does Not Affect Leptin Sensitivity

    PubMed Central

    Stefater, Margaret A; Pérez-Tilve, Diego; Chambers, Adam P; Wilson-Pérez, Hilary E; Sandoval, Darleen A; Berger, José; Toure, Mouhamadoul; Tschöep, Matthias; Woods, Stephen C; Seeley, Randy J

    2010-01-01

    Background & Aims Surgical intervention produces sustainable weight loss and metabolic improvement in obese individuals. Vertical sleeve gastrectomy (VSG) produces dramatic, sustained weight loss; we investigated whether these changes result from improved sensitivity to leptin. Methods VSG was performed in Long-Evans rats with diet-induced obesity. Naïve or sham-operated rats, fed either ad libitum or pair-fed with the VSG group, were used as controls. Following surgery, body weights and food intake were monitored. We investigated energy expenditure, meal patterns, leptin sensitivity, and expression of pro-opiomelanocortin (POMC)/agouti-related peptide (AgRP)/neuropeptide Y (NPY) in the hypothalamus of the rats. Results We observed sustained losses in weight and body fat in male and female rats after VSG. Weight loss persisted after the disappearance of a transient, post-surgical food intake reduction. Resting energy expenditure was similar between control and VSG rats. VSG rats maintained their reduced body weights. However, they responded to a chronic food restriction challenge by overeating, which resulted in pre-restriction, rather than pre-VSG, body weights. Consistent with lower adiposity, VSG decreased plasma leptin levels. Although VSG slightly improved leptin’s anorectic action, the response was comparable to that observed in controls matched for adiposity by caloric restriction. Changes in hypothalamic neuropeptide expression were consistent with the lower body weight and lower leptin levels but cannot account for the sustained weight loss. Conclusions VSG causes sustained reduction in body weight, which results from loss of fat mass. The maintenance of weight loss observed did not result from changes in sensitivity to leptin. PMID:20226189

  2. Loss of Free Fatty Acid Receptor 2 leads to impaired islet mass and beta cell survival

    PubMed Central

    Villa, Stephanie R.; Priyadarshini, Medha; Fuller, Miles H.; Bhardwaj, Tanya; Brodsky, Michael R.; Angueira, Anthony R.; Mosser, Rockann E.; Carboneau, Bethany A.; Tersey, Sarah A.; Mancebo, Helena; Gilchrist, Annette; Mirmira, Raghavendra G.; Gannon, Maureen; Layden, Brian T.

    2016-01-01

    The regulation of pancreatic β cell mass is a critical factor to help maintain normoglycemia during insulin resistance. Nutrient-sensing G protein-coupled receptors (GPCR) contribute to aspects of β cell function, including regulation of β cell mass. Nutrients such as free fatty acids (FFAs) contribute to precise regulation of β cell mass by signaling through cognate GPCRs, and considerable evidence suggests that circulating FFAs promote β cell expansion by direct and indirect mechanisms. Free Fatty Acid Receptor 2 (FFA2) is a β cell-expressed GPCR that is activated by short chain fatty acids, particularly acetate. Recent studies of FFA2 suggest that it may act as a regulator of β cell function. Here, we set out to explore what role FFA2 may play in regulation of β cell mass. Interestingly, Ffar2−/− mice exhibit diminished β cell mass at birth and throughout adulthood, and increased β cell death at adolescent time points, suggesting a role for FFA2 in establishment and maintenance of β cell mass. Additionally, activation of FFA2 with Gαq/11-biased agonists substantially increased β cell proliferation in in vitro and ex vivo proliferation assays. Collectively, these data suggest that FFA2 may be a novel therapeutic target to stimulate β cell growth and proliferation. PMID:27324831

  3. Loss of Free Fatty Acid Receptor 2 leads to impaired islet mass and beta cell survival.

    PubMed

    Villa, Stephanie R; Priyadarshini, Medha; Fuller, Miles H; Bhardwaj, Tanya; Brodsky, Michael R; Angueira, Anthony R; Mosser, Rockann E; Carboneau, Bethany A; Tersey, Sarah A; Mancebo, Helena; Gilchrist, Annette; Mirmira, Raghavendra G; Gannon, Maureen; Layden, Brian T

    2016-01-01

    The regulation of pancreatic β cell mass is a critical factor to help maintain normoglycemia during insulin resistance. Nutrient-sensing G protein-coupled receptors (GPCR) contribute to aspects of β cell function, including regulation of β cell mass. Nutrients such as free fatty acids (FFAs) contribute to precise regulation of β cell mass by signaling through cognate GPCRs, and considerable evidence suggests that circulating FFAs promote β cell expansion by direct and indirect mechanisms. Free Fatty Acid Receptor 2 (FFA2) is a β cell-expressed GPCR that is activated by short chain fatty acids, particularly acetate. Recent studies of FFA2 suggest that it may act as a regulator of β cell function. Here, we set out to explore what role FFA2 may play in regulation of β cell mass. Interestingly, Ffar2(-/-) mice exhibit diminished β cell mass at birth and throughout adulthood, and increased β cell death at adolescent time points, suggesting a role for FFA2 in establishment and maintenance of β cell mass. Additionally, activation of FFA2 with Gαq/11-biased agonists substantially increased β cell proliferation in in vitro and ex vivo proliferation assays. Collectively, these data suggest that FFA2 may be a novel therapeutic target to stimulate β cell growth and proliferation. PMID:27324831

  4. DXA, bioelectrical impedance, ultrasonography and biometry for the estimation of fat and lean mass in cats during weight loss

    PubMed Central

    2012-01-01

    Background Few equations have been developed in veterinary medicine compared to human medicine to predict body composition. The present study was done to evaluate the influence of weight loss on biometry (BIO), bioimpedance analysis (BIA) and ultrasonography (US) in cats, proposing equations to estimate fat (FM) and lean (LM) body mass, as compared to dual energy x-ray absorptiometry (DXA) as the referenced method. For this were used 16 gonadectomized obese cats (8 males and 8 females) in a weight loss program. DXA, BIO, BIA and US were performed in the obese state (T0; obese animals), after 10% of weight loss (T1) and after 20% of weight loss (T2). Stepwise regression was used to analyze the relationship between the dependent variables (FM, LM) determined by DXA and the independent variables obtained by BIO, BIA and US. The better models chosen were evaluated by a simple regression analysis and means predicted vs. determined by DXA were compared to verify the accuracy of the equations. Results The independent variables determined by BIO, BIA and US that best correlated (p < 0.005) with the dependent variables (FM and LM) were BW (body weight), TC (thoracic circumference), PC (pelvic circumference), R (resistance) and SFLT (subcutaneous fat layer thickness). Using Mallows’Cp statistics, p value and r2, 19 equations were selected (12 for FM, 7 for LM); however, only 7 equations accurately predicted FM and one LM of cats. Conclusions The equations with two variables are better to use because they are effective and will be an alternative method to estimate body composition in the clinical routine. For estimated lean mass the equations using body weight associated with biometrics measures can be proposed. For estimated fat mass the equations using body weight associated with bioimpedance analysis can be proposed. PMID:22781317

  5. Strategy for the customized mass screening of genetic sensorineural hearing loss in koreans.

    PubMed

    Chang, Mun Young; Choi, Byung Yoon

    2014-09-01

    Hearing loss is one of the most common sensorineural disorder. More than half of congenital bilateral profound deafness cases have been estimated to be attributed to genetic cause. Identification of genetic cause can provide valuable information. We developed new diagnostic strategy combining phenotype-driven candidate gene approach and targeted exome sequencing to find out the causative mutation of hearing loss. The causative mutation detection rates of this strategy were 78.1% and 54.8% in Korean multiplex families and sporadic severe to profound hearing loss families, respectively. The most frequent causative genes of Korean multiplex families were SLC26A4 and POU3F4. The other causative genes were MRNR1, WFS1, COCH, TECTA, MYO6, COL11A2, EYA4, GJB3, OTOF, STRC, MYO3A, and GJB2. The most frequent causative gene of Korean sporadic severe to profound hearing loss families was SLC26A4 followed by GJB2, CHD7, and CDH23. Based upon the results, the value of this strategy as a diagnostic tool seems to be promising. Although whole genome and exome sequencing have advanced as the development of next-generation sequencing, this new strategy could be a good screening and diagnostic tool to find the causative mutations. PMID:25279224

  6. Strategy for the Customized Mass Screening of Genetic Sensorineural Hearing Loss in Koreans

    PubMed Central

    Chang, Mun Young

    2014-01-01

    Hearing loss is one of the most common sensorineural disorder. More than half of congenital bilateral profound deafness cases have been estimated to be attributed to genetic cause. Identification of genetic cause can provide valuable information. We developed new diagnostic strategy combining phenotype-driven candidate gene approach and targeted exome sequencing to find out the causative mutation of hearing loss. The causative mutation detection rates of this strategy were 78.1% and 54.8% in Korean multiplex families and sporadic severe to profound hearing loss families, respectively. The most frequent causative genes of Korean multiplex families were SLC26A4 and POU3F4. The other causative genes were MRNR1, WFS1, COCH, TECTA, MYO6, COL11A2, EYA4, GJB3, OTOF, STRC, MYO3A, and GJB2. The most frequent causative gene of Korean sporadic severe to profound hearing loss families was SLC26A4 followed by GJB2, CHD7, and CDH23. Based upon the results, the value of this strategy as a diagnostic tool seems to be promising. Although whole genome and exome sequencing have advanced as the development of next-generation sequencing, this new strategy could be a good screening and diagnostic tool to find the causative mutations. PMID:25279224

  7. H2O vapor excitation in dusty AGB envelopes. A PACS view of OH 127.8+0.0

    NASA Astrophysics Data System (ADS)

    Lombaert, R.; Decin, L.; de Koter, A.; Blommaert, J. A. D. L.; Royer, P.; De Beck, E.; de Vries, B. L.; Khouri, T.; Min, M.

    2013-06-01

    Context. AGB stars lose a large percentage of their mass in a dust-driven wind. This creates a circumstellar envelope, which can be studied through thermal dust emission and molecular emission lines. In the case of high mass-loss rates, this study is complicated by the high optical depths and the intricate coupling between gas and dust radiative transfer characteristics. An important aspect of the physics of gas-dust interactions is the strong influence of dust on the excitation of several molecules, including H2O. Aims: The dust and gas content of the envelope surrounding the high mass-loss rate OH/IR star OH 127.8+0.0, as traced by Herschel observations, is studied, with a focus on the H2O content and the dust-to-gas ratio. We report detecting a large number of H2O vapor emission lines up to J = 9 in the Herschel data, for which we present the measured line strengths. Methods: The treatments of both gas and dust species are combined using two numerical radiative transfer codes. The method is illustrated for both low and high mass-loss-rate sources. Specifically, we discuss different ways of assessing the dust-to-gas ratio: 1) from the dust thermal emission spectrum and the CO molecular gas line strengths; 2) from the momentum transfer from dust to gas and the measured gas terminal velocity; and 3) from the determination of the required amount of dust to reproduce H2O lines for a given H2O vapor abundance. These three diagnostics probe different zones of the outflow, for the first time allowing an investigation of a possible radial dependence of the dust-to-gas ratio. Results: We modeled the infrared continuum and the CO and H2O emission lines in OH 127.8+0.0 simultaneously. We find a dust-mass-loss rate of (0.5 ± 0.1) × 10-6 M⊙ yr-1 and an H2O ice fraction of 16% ± 2% with a crystalline-to-amorphous ratio of 0.8 ± 0.2. The gas temperature structure is modeled with a power law, leading to a constant gas-mass-loss rate between 2 × 10-5 M⊙ yr-1 and 1 × 10

  8. Mass Dependent and Mass Independent Fractionation of Hg Isotopes and Estimation of Photochemical Loss of Hg in Aquatic Systems

    NASA Astrophysics Data System (ADS)

    Bergquist, B. A.; Blum, J. D.

    2007-12-01

    Mercury is a globally distributed and highly toxic pollutant, the mobility and bioaccumulation of which is dependent on its redox cycling. Hg isotope analysis is an important new tool for identifying Hg sources and tracking Hg transformations in the environment. Most natural samples analyzed for Hg isotopes display mass-dependent isotope fractionation (MDF), but a small body of data suggests that some natural samples also display mass- independent isotope fractionation (MIF) of the odd Hg isotopes. Here we document MIF of Hg isotopes during an important natural process, constrain the potential mechanism of isotope fractionation, and apply the MIF observed in natural samples to quantify the photochemical reduction of Hg species in the environment. Reduction of Hg species to Hg0 vapor is an important pathway for removal of Hg from aqueous systems into the atmosphere and occurs by abiotic and biotic mechanisms. In laboratory experiments, we find that photochemical reduction Hg species by natural sunlight leads to large MIF of the odd isotopes. Also, the relationship between MIF for the two odd isotopes of Hg is significantly different for different photo-reduction pathways. In contrast, both biological reduction (Kritee et al., 2006) and dark abiotic organically-mediated reduction follow MDF. Natural samples from aquatic ecosystems preserve both MDF and MIF. In fish, MDF increases with the size and Hg concentration of fish suggesting MDF may be useful in understanding Hg bioaccumulation. Fish also display a large range in MIF (4‰), and the relationship between the MIF of the two odd isotopes in fish has a similar slope to the slope found for photo-reduction of CH3Hg+. Since fish bioaccumulate CH3Hg+, fish may be recording the extent to which CH3Hg+ is lost via photochemical reduction in an aquatic ecosystem. Fish populations from different locations have different MIF values, but mostly display similar MIF within a given locale. This suggests that MIF is preserved

  9. Examining the Impact of Early AGB Nucleosynthesis on the Apparent Cosmological Variation in the Fine Structure Constant

    NASA Astrophysics Data System (ADS)

    Ashenfelter, Timothy; Mathews, Grant; Olive, Keith

    2004-10-01

    Evidence from a large sample of quasar absorption-line spectra in damped Lyman-α systems has shown potential cosmological variation of the fine structure constant α. The most statistically significant portion of this sample involves the comparison of Mg and Fe wavelength shifts using the many-multiplet (MM) method. However, this method is sensitive to the heavy isotopes, especially in Mg. We implement recent yields of intermediate mass (IM) stars, which evolve beyond the CNO cycle, to show that the ensuing isotope distribution of Mg can account for the observed variation in α provided early star-formation was particularly rich in IM stars. During the Asymptotic Giant Branch (AGB) phase of IM stars, heavy Mg isotopes are robustly produced via hot-bottom burning and thermal pulsing in helium burning shell. We incorporate these recently appreciated processes in the galactic chemical evolution models of these damped Lyman-α systems (early galaxies) and delve into the consequences of this chemical evolution alternative to an α variation. We find that this analysis adds to the mounting evidence that the low-metallicity Universe was strongly influenced by IM stars beyond the standard power law distribution of stellar masses. Because these AGB stars have a significant influence on other abundances, especially nitrogen, we use measurements of N, Si Fe, C, and O to constrain our models. In this way, we obtain an alternative explanation of the α variation that is consistent with observations.

  10. NanoSIMS studies of Ba isotopic compositions in single presolar silicon carbide grains from AGB stars and supernovae

    NASA Astrophysics Data System (ADS)

    Marhas, K. K.; Hoppe, P.; Ott, U.

    2007-08-01

    We have studied 74 single presolar silicon carbide grains with sizes between 0.2 and 2.6 μm from the Murchison and Murray meteorites for Ba isotopic compositions using NanoSIMS. We also analyzed 7 SiC particles either consisting of sub-micron-size SiC grains or representing a morphologically and isotopically distinct subgroup. Of the 55 (likely) mainstream grains, origina