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Sample records for agb asymptotic giant

  1. 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.

  2. 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.

  3. 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.

  4. Near-infrared Observations of SiO Maser-emitting Asymptotic Giant Branch (AGB) Stars

    NASA Astrophysics Data System (ADS)

    Chibueze, James O.; Miyahara, Takeshi; Omodaka, Toshihiro; Ohta, Takashi; Fujii, Takahiro; Tanaka, Masuo; Motohara, Kentaro; Makoto, Miyoshi

    2016-02-01

    Near-infrared (NIR) monitoring observations of asymptotic giant branch stars exciting bright SiO masers have been made with the 1 m telescope of Kagoshima University. In order to investigate the properties of these stars and their envelopes, we combined our NIR photometric data with mid- and far-infrared flux data obtained by the IRAS satellite, SiO maser flux data provided by the Nobeyama Radio Observatory, visual magnitude data provided by the AAVSO, and the reported data on the expansion velocities of the circumstellar envelopes. The absolute magnitudes at the K-band and the distances are estimated using the period-luminosity relation of Mira variables determined by Feast et al. Then, mass-loss rates and isotropic luminosities of an SiO maser are estimated. The mass-loss rates range from approximately 10-8 {M}⊙ \\{{yr}}-1 to over 10-5 {M}⊙ {{yr}}-1. We found that the NIR pulsation amplitudes are correlated with the pulsation periods and the observed wavelengths. We also found correlations of the isotropic luminosities of SiO masers with the mass-loss rates and absolute magnitudes at the K-band. These results will help us to understand the pumping mechanism of SiO masers. We measured, for the first time, the periods and/or NIR magnitudes of TX Cam, BW Cam, IRAS 06297+4045, IRAS 18387-0423, and RT Cep.

  5. Luminous asymptotic giant branch stars in the Large Magellanic Cloud

    NASA Technical Reports Server (NTRS)

    Reid, Neill; Tinney, Chris; Mould, Jeremy

    1990-01-01

    A search has been conducted for optically obscured asymptotic giant branch (AGB) stars in the LMC. The results obtained are noted to rule out the presence of sufficient high-luminosity 'cocoon' stars to explain the observed deficit of several hundred luminous AGB stars between the predictions of standard AGB evolution models and the observed luminosity function. Bolometric magnitudes as low as -5 are inferred for these sources; it is suggested that this phase can be triggered at low luminosities, truncating AGB evolution and leading to the observed scarcity of AGBs with M(bol) greater than -6.0 mag.

  6. Simulated asymptotic giant branch populations for Magellanic Cloud clusters

    SciTech Connect

    Frantsman, IU.L.

    1986-04-01

    An approximate numerical calculation for an evolving 100,000-star cluster simulates the asymptotic giant branch (AGB) populations of two Magellanic Cloud globular clusters. Several laws of mass loss by AGB stars and various initial heavy-element abundances and cluster ages are considered. In the H-R diagram the early-AGB stars differ in both luminosity and Teff from AGB stars passing through the helium shell thermal-flash stage. The numbers of M- and C-type stars in this second phase are predicted for model clusters with different parameters. 18 references.

  7. Nucleosynthesis in asymptotic giant branch stars

    SciTech Connect

    El Eid, Mounib F.

    2014-05-09

    The nucleosynthesis in asymptotic giant branch stars (briefly: AGB)is a challenging and fascinating subject in the theory of stellar evolution and important for observations as well. This is because about of half the heavy elements beyond iron are synthesized during thermal pulsation phases of these stars. Furthermore, the understanding of the production of the heavy elements and some light elements like carbon and fluorine represent a powerful tool to get more insight into the internal structure of these stars. The diversity of nuclear processing during the AGB phases may also motivate experimental activities in measuring important nuclear reactions. In this contribution, we emphasize several interesting feature of the nucleosynthesis in AGB stars which still needs further elaboration especially from theoretical point of view.

  8. Stardust from Asymptotic Giant Branch Stars

    NASA Astrophysics Data System (ADS)

    Gail, H.-P.; Zhukovska, S. V.; Hoppe, P.; Trieloff, M.

    2009-06-01

    The formation of dust in the outflows of low- and intermediate-mass stars on the first giant branch and asymptotic giant branch (AGB) is studied and the relative contributions of stars of different initial masses and metallicities to the interstellar medium (ISM) at the instant of solar system formation are derived. These predictions are compared with the characteristics of the parent stars of presolar dust grains found in primitive meteorites and interplanetary dust particles (IDPs) inferred from their isotopic compositions. For this purpose, model calculations for dust condensation in stellar outflows are combined with synthetic models of stellar evolution on the first giant branch and AGB and an evolution model of the Milky Way for the solar neighborhood. The dust components considered are olivine, pyroxene, carbon, SiC, and iron. The corresponding dust production rates are derived for the solar vicinity. From these rates and taking into account dust destruction by supernova shocks in the ISM, the contributions to the inventory of presolar dust grains in the solar system are derived for stars of different initial masses and metallicities. It is shown that stars on the first giant branch and the early AGB are not expected to form dust, in accord with astronomical observations. Dust formation is concentrated in the last phase of evolution, the thermally pulsing AGB. Due to the limited lifetime of dust grains in the ISM only parent stars from a narrow range of metallicities are expected to contribute to the population of presolar dust grains. Silicate and silicon carbide dust grains are predicted to come from parent stars with metallicities not less than about Z ≈ 0.008 (0.6 × solar). This metallicity limit is higher than that inferred from presolar SiC grain isotope data. The population of presolar carbon dust grains is predicted to originate from a wider range of metallicities, down to Z ≈ 0.004. Masses of AGB stars that produce C-rich dust are in the range

  9. 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.

  10. Introduction to Asymptotic Giant Branch Stars

    NASA Astrophysics Data System (ADS)

    El Eid, Mounib F.

    2016-04-01

    A brief introduction on the main characteristics of the asymptotic giant branch stars (briefly: AGB) is presented. We describe a link to observations and outline basic features of theoretical modeling of these important evolutionary phases of stars. The most important aspects of the AGB stars is not only because they are the progenitors of white dwarfs, but also they represent the site of almost half of the heavy element formation beyond iron in the galaxy. These elements and their isotopes are produced by the s-process nucleosynthesis, which is a neutron capture process competing with the β- radioactive decay. The neutron source is mainly due to the reaction 13C(α,n)16O reaction. It is still a challenging problem to obtain the right amount of 13 C that can lead to s-process abundances compatible with observation. Some ideas are presented in this context.

  11. Rubidium-rich asymptotic giant branch stars.

    PubMed

    García-Hernández, D A; García-Lario, P; Plez, B; D'Antona, F; Manchado, A; Trigo-Rodríguez, J M

    2006-12-15

    A long-debated issue concerning the nucleosynthesis of neutron-rich elements in asymptotic giant branch (AGB) stars is the identification of the neutron source. We report intermediate-mass (4 to 8 solar masses) AGB stars in our Galaxy that are rubidium-rich as a result of overproduction of the long-lived radioactive isotope (87)Rb, as predicted theoretically 40 years ago. This finding represents direct observational evidence that the (22)Ne(alpha,n)(25)Mg reaction must be the dominant neutron source in these stars. These stars challenge our understanding of the late stages of the evolution of intermediate-mass stars and would have promoted a highly variable Rb/Sr environment in the early solar nebula. PMID:17095658

  12. A Catalog of GALEX Ultraviolet Emission from Asymptotic Giant Branch Stars

    NASA Astrophysics Data System (ADS)

    Montez, Rodolfo; Ramstedt, Sofia; Kastner, Joel H.; Vlemmings, Wouter

    2016-06-01

    We present the results of a search for ultraviolet emission from stars on the asymptotic giant branch (AGB). Our input sample of nearly 500 AGB stars were selected from existing catalogs, as detailed in the our earlier search for X-ray emission from AGB stars (Ramstedt et al. 2012). We determined that 67% of the input sample were observed in the imaging surveys of the Galaxy Evolution Explorer (GALEX). More than half of the individual AGB stars observed by GALEX were detected in at least one of the NUV or FUV bandpasses. The sample of NUV- and FUV-detected AGB stars includes a range of chemical types (M-, C-, and S-types) that when combined with multiwavelength photometry indicate the influence of the distinct circumstellar environments. We analyze multiwavelength photometry for both the detections and non-detections to maximize the return from this emerging UV view of cool, evolved, mass losing giants.

  13. Chemical Analysis of Asymptotic Giant Branch Stars in M62

    NASA Astrophysics Data System (ADS)

    Lapenna, E.; Mucciarelli, A.; Ferraro, F. R.; Origlia, L.; Lanzoni, B.; Massari, D.; Dalessandro, E.

    2015-11-01

    We have collected UVES-FLAMES high-resolution spectra for a sample of 6 asymptotic giant branch (AGB) and 13 red giant branch (RGB) stars in the Galactic globular cluster (GC) M62 (NGC 6266). Here we present the detailed abundance analysis of iron, titanium, and light elements (O, Na, Mg, and Al). For the majority (five out of six) of the AGB targets, we find that the abundances of both iron and titanium determined from neutral lines are significantly underestimated with respect to those obtained from ionized features, the latter being, instead, in agreement with those measured for the RGB targets. This is similar to recent findings in other clusters and may suggest the presence of nonlocal thermodynamic equilibrium (NLTE) effects. In the O-Na, Al-Mg, and Na-Al planes, the RGB stars show the typical correlations observed for GC stars. Instead, all the AGB targets are clumped in the regions where first-generation stars are expected to lie, similar to what was recently found for the AGB population of NGC 6752. While the sodium and aluminum abundances could be underestimated as a consequence of the NLTE bias affecting iron and titanium, the oxygen line used does not suffer from the same effects, and the lack of O-poor AGB stars therefore is a solid result. We can thus conclude that none of the investigated AGB stars belongs to the second stellar generation of M62. We also find an RGB star with extremely high sodium abundance ([Na/Fe] = +1.08 dex). Based on observations collected at the ESO-VLT (Cerro Paranal, Chile) under program 193.D-0232. Also based on observations (GO10120 and GO11609) with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.

  14. The red/infrared evolution in galaxies - Effect of the stars on the asymptotic giant branch

    NASA Technical Reports Server (NTRS)

    Chokshi, Arati; Wright, Edward L.

    1987-01-01

    The effect of including the asymptotic giant branch (AGB) population in a spectral synthesis model of galaxy evolution is examined. Stars on the AGB are luminous enough and also evolve rapidly enough to affect the evolution of red and infrared colors in galaxies. The validity of using infrared colors as distance indicators to galaxies is then investigated in detail. It is found that for z of 1 or less infrared colors of model galaxies behave linearly with redshift.

  15. Stellar Properties of Asymptotic Giant Branch Stars in the Dwarf Irregular Galaxy IC 1613

    NASA Astrophysics Data System (ADS)

    Chun, S.-H.; Jung, M. Y.; Kang, M.; Jung, D.; Sohn, Y.-J.

    2015-08-01

    Broadband near-infrared images obtained with the WIRCam array of the Canada-France-Hawaii Telescope are used to investigate the properties of resolved asymptotic giant branch (AGB) stars in the dwarf irregular galaxy IC 1613. Combining our JHKs data with optical photometric data, AGB stars were selected in color-magnitude diagrams covering a wide range of wavelength. We examined the distribution of AGB stars in the (J-Ks, H-Ks) color-color diagram, and distinguished 140 carbon-rich and 306 oxygen-rich M giant AGB stars. The number ratio of C stars to M giants (C/M) was estimated, and the metallicity of IC 1613 was derived using the C/M ratio. We also examined the local C/M ratio as a function of radial distance from the center of the galaxy, and found a small negative gradient.

  16. Stellar Yields from Metal-rich Asymptotic Giant Branch Models

    NASA Astrophysics Data System (ADS)

    Karakas, Amanda I.; Lugaro, Maria

    2016-07-01

    We present new theoretical stellar yields and surface abundances for three grids of metal-rich asymptotic giant branch (AGB) models. Post-processing nucleosynthesis results are presented for stellar models with initial masses between 1 M ⊙ and 7.5 M ⊙ for Z = 0.007, and 1 M ⊙ and 8 M ⊙ for Z = 0.014 (solar) and Z = 0.03. We include stellar surface abundances as a function of thermal pulse on the AGB for elements from C to Bi and for a selection of isotopic ratios for elements up to Fe and Ni (e.g., {}12{{C}}/{}13{{C}}), which can be obtained from observations of molecules in stars and from the laboratory analysis of meteoritic stardust grains. Ratios of elemental abundances of He/H, C/O, and N/O are also included, which are useful for direct comparison to observations of AGB stars and their progeny, including planetary nebulae. The integrated elemental stellar yields are presented for each model in the grid for hydrogen, helium, and all stable elements from C to Bi. Yields of Li are also included for intermediate-mass models with hot bottom burning. We present the first slow neutron-capture (s-process) yields for super solar metallicity AGB stars with Z = 0.03, and the first complete s-process yields for models more massive than 6 M ⊙ at all three metallicities.

  17. Cyanogen in NGC 1851 Red Giant Branch and Asymptotic Giant Branch Stars: Quadrimodal Distributions

    NASA Astrophysics Data System (ADS)

    Campbell, S. W.; Yong, D.; Wylie-de Boer, E. C.; Stancliffe, R. J.; Lattanzio, J. C.; Angelou, G. C.; D'Orazi, V.; Martell, S. L.; Grundahl, F.; Sneden, C.

    2012-12-01

    The Galactic globular cluster NGC 1851 has raised much interest since Hubble Space Telescope photometry revealed that it hosts a double subgiant branch. Here we report on our homogeneous study into the cyanogen (CN) band strengths in the red giant branch (RGB) population (17 stars) and asymptotic giant branch (AGB) population (21 stars) using AAOmega/2dF spectra with R ~ 3000. We discover that NGC 1851 hosts a quadrimodal distribution of CN band strengths in its RGB and AGB populations. This result supports the merger formation scenario proposed for this cluster, such that the CN quadrimodality could be explained by the superposition of two "normal" bimodal populations. A small sample overlap with an abundance catalog allowed us to tentatively explore the relationship between our CN populations and a range of elemental abundances. We found a striking correlation between CN and [O/Na]. We also found that the four CN peaks may be paired—the two CN-weaker populations being associated with low Ba and the two CN-stronger populations with high Ba. If true, then s-process abundances would be a good diagnostic for disentangling the two original clusters in the merger scenario. More observations are needed to confirm the quadrimodality and also the relationship between the subpopulations. We also report CN results for NGC 288 as a comparison. Our relatively large samples of AGB stars show that both clusters have a bias toward CN-weak AGB populations.

  18. CYANOGEN IN NGC 1851 RED GIANT BRANCH AND ASYMPTOTIC GIANT BRANCH STARS: QUADRIMODAL DISTRIBUTIONS

    SciTech Connect

    Campbell, S. W.; Stancliffe, R. J.; Lattanzio, J. C.; Angelou, G. C.; D'Orazi, V.; Yong, D.; Wylie-de Boer, E. C.; Martell, S. L.; Grundahl, F.; Sneden, C. E-mail: david.yong@anu.edu.au

    2012-12-10

    The Galactic globular cluster NGC 1851 has raised much interest since Hubble Space Telescope photometry revealed that it hosts a double subgiant branch. Here we report on our homogeneous study into the cyanogen (CN) band strengths in the red giant branch (RGB) population (17 stars) and asymptotic giant branch (AGB) population (21 stars) using AAOmega/2dF spectra with R {approx} 3000. We discover that NGC 1851 hosts a quadrimodal distribution of CN band strengths in its RGB and AGB populations. This result supports the merger formation scenario proposed for this cluster, such that the CN quadrimodality could be explained by the superposition of two 'normal' bimodal populations. A small sample overlap with an abundance catalog allowed us to tentatively explore the relationship between our CN populations and a range of elemental abundances. We found a striking correlation between CN and [O/Na]. We also found that the four CN peaks may be paired-the two CN-weaker populations being associated with low Ba and the two CN-stronger populations with high Ba. If true, then s-process abundances would be a good diagnostic for disentangling the two original clusters in the merger scenario. More observations are needed to confirm the quadrimodality and also the relationship between the subpopulations. We also report CN results for NGC 288 as a comparison. Our relatively large samples of AGB stars show that both clusters have a bias toward CN-weak AGB populations.

  19. Obscured Asymptotic Giant Branch Stars in the Magellanic Clouds

    NASA Astrophysics Data System (ADS)

    van Loon, J. T.

    The most drastic change in the life of an intermediate mass star occurs when it approaches the tip of the Asymptotic Giant Branch (AGB). Large amplitude pulsation of the stellar photosphere and favourable conditions for dust formation cause these stars to develop heavy mass loss, leading to the star's death. The dusty circumstellar envelope (CSE) obscures the optical light from the star and re-emits at longer wavelengths, making it a very bright infrared (IR) object. The physical mechanism of the mass loss and its temporal behaviour are not understood. AGB stars can be best studied in either of the Magellanic Clouds, as these stars are all at nearly the same, well known distance to us, and suffer relatively little interstellar extinction. The Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) have metallicities a factor ~ 2 and 5 lower than the Milky Way, hence the metallicity dependence of the evolution and mass loss of AGB stars can be studied. A significant number of obscured AGB stars have been found in the Magellanic Clouds only very recently (Loup et al. 1997; Zijlstra et al. 1996; van Loon et al. 1997, 1998a; Groenewegen and Blommaert 1998). I first briefly describe our searches for AGB stars as counterparts of IRAS point sources in the Magellanic Clouds, using near-IR photometers and arrays. IR spectrophotometry and spectroscopy from the ground and from space (IRAS and ISO) are used to classify the stars as oxygen or carbon rich AGB stars. Both oxygen and carbon stars can be found at all luminosities from 6,000 to 40,000 Lo. Luminous carbon stars are the result of a reduced envelope mass due to mass loss, switching off Hot Bottom Burning. Near-IR monitoring has resulted in known periods and amplitudes for the obscured AGB stars in the Large Magellanic Cloud. The period-luminosity diagram of these Long Period Variables (LPVs) indicates the occurrence of thermal pulses. I show that the reddest stars, with the optically thickest CSEs, are not the

  20. THE FIRST FLUORINE ABUNDANCE DETERMINATIONS IN EXTRAGALACTIC ASYMPTOTIC GIANT BRANCH CARBON STARS

    SciTech Connect

    Abia, C.; Cristallo, S.; Dominguez, I.; Cunha, K.; Smith, V. V.; De Laverny, P.; Recio-Blanco, A.; Straniero, O.

    2011-08-10

    Fluorine ({sup 19}F) abundances (or upper limits) are derived in six extragalactic asymptotic giant branch (AGB) carbon stars from the HF(1-0) R9 line at 2.3358 {mu}m in high-resolution spectra. The stars belong to the Local Group galaxies, Large Magellanic Cloud, Small Magellanic Cloud, and Carina dwarf spheroidal, spanning more than a factor of 50 in metallicity. This is the first study to probe the behavior of F with metallicity in intrinsic extragalactic C-rich AGB stars. Fluorine could be measured only in four of the target stars, showing a wide range in F enhancements. Our F abundance measurements together with those recently derived in Galactic AGB carbon stars show a correlation with the observed carbon and s-element enhancements. The observed correlations, however, display a different dependence on the stellar metallicity with respect to theoretical predictions in low-mass, low-metallicity AGB models. We briefly discuss the possible reasons for this discrepancy. If our findings are confirmed in a larger number of metal-poor AGBs, the issue of F production in AGB stars will need to be revisited.

  1. Neutron sources and neutron-capture paths in asymptotic giant branch stars

    NASA Astrophysics Data System (ADS)

    Maria, Lugaro

    2016-04-01

    Roughly half of the abundances of the elements heavier than iron in the cosmos are produced by slow neutron captures (the s process) in hydrostatic conditions when the neutron density is below roughly 1013 n/cm-3. While it is observationally well confirmed that asymptotic giant branch (AGB) stars are the main site of the s process, we are still facing many problems in the theoretical models and nuclear inputs. Major current issues are the effect of stellar rotation and magnetic fields and the determination of the rate of the neutron source reactions. I will present these problems and discuss the observational constraints that can help us to solve them, including spectroscopically derived abundances, meteoritic stardust, and stellar seismology. Further, I will present evidence that the s process is not the only neutron-capture process to occur in AGB stars: an intermediate process is also required to explain recent observations of post-AGB stars.

  2. SiO AND H{sub 2}O MASER SURVEY TOWARD POST-ASYMPTOTIC GIANT BRANCH AND ASYMPTOTIC GIANT BRANCH STARS

    SciTech Connect

    Yoon, Dong-Hwan; Park, Yong-Sun; Cho, Se-Hyung; Kim, Jaeheon; Yun, Young joo E-mail: yspark@astro.snu.ac.kr E-mail: jhkim@kasi.re.kr

    2014-03-01

    We performed simultaneous observations of SiO v = 1, 2, {sup 29}SiO v = 0, J = 1-0 and H{sub 2}O 6{sub 16}-5{sub 23} maser lines toward 143 AGB and 164 post-asymptotic giant branch (AGB) stars in order to investigate how evolutionary characteristics from AGB to post-AGB stars appear in both SiO and H{sub 2}O maser emissions. The observations were carried out from 2011 February to 2012 March using the Korean VLBI Network single-dish telescopes. We have detected SiO and/or H{sub 2}O maser emission from 21 sources out of 164 post-AGB stars including 12 new detections. Of 143 AGB stars, we detected SiO and/or H{sub 2}O maser emission from 44 stars including 24 new detections. SiO v = 2, J = 1-0 maser emission without a SiO v = 1 maser was detected from 7 sources among 14 SiO-detected post-AGB stars, and the intensity of the SiO v = 2, J = 1-0 maser tends to be much stronger than that of SiO v = 1, which is different from those of AGB stars. This may be related to the development of hot dust shells according to the evolutionary processes of post-AGB stars. We also found that both SiO and H{sub 2}O masers were detected in the blue group (LI, or Left of IRAS), while only the H{sub 2}O maser was detected in the red group (RI, or Right of IRAS) for post-AGB stars. These different detection rates between SiO and H{sub 2}O masers may originate from the different abundances of masing molecules in the circumstellar envelope according to the different mass and expansion velocity between LI and RI regions together with their evolutionary stages.

  3. THE ACS NEARBY GALAXY SURVEY TREASURY. IX. CONSTRAINING ASYMPTOTIC GIANT BRANCH EVOLUTION WITH OLD METAL-POOR GALAXIES

    SciTech Connect

    Girardi, Leo; Williams, Benjamin F.; Gilbert, Karoline M.; Rosenfield, Philip; Dalcanton, Julianne J.; Marigo, Paola; Boyer, Martha L.; Dolphin, Andrew; Weisz, Daniel R.; Skillman, Evan; Melbourne, Jason; Olsen, Knut A. G.; Seth, Anil C.

    2010-12-01

    In an attempt to constrain evolutionary models of the asymptotic giant branch (AGB) phase at the limit of low masses and low metallicities, we have examined the luminosity functions and number ratios between AGB and red giant branch (RGB) stars from a sample of resolved galaxies from the ACS Nearby Galaxy Survey Treasury. This database provides Hubble Space Telescope optical photometry together with maps of completeness, photometric errors, and star formation histories for dozens of galaxies within 4 Mpc. We select 12 galaxies characterized by predominantly metal-poor populations as indicated by a very steep and blue RGB, and which do not present any indication of recent star formation in their color-magnitude diagrams. Thousands of AGB stars brighter than the tip of the RGB (TRGB) are present in the sample (between 60 and 400 per galaxy), hence, the Poisson noise has little impact in our measurements of the AGB/RGB ratio. We model the photometric data with a few sets of thermally pulsing AGB (TP-AGB) evolutionary models with different prescriptions for the mass loss. This technique allows us to set stringent constraints on the TP-AGB models of low-mass, metal-poor stars (with M < 1.5 M{sub sun}, [Fe/H]{approx}< -1.0). Indeed, those which satisfactorily reproduce the observed AGB/RGB ratios have TP-AGB lifetimes between 1.2 and 1.8 Myr, and finish their nuclear burning lives with masses between 0.51 and 0.55 M{sub sun}. This is also in good agreement with recent observations of white dwarf masses in the M4 old globular cluster. These constraints can be added to those already derived from Magellanic Cloud star clusters as important mileposts in the arduous process of calibrating AGB evolutionary models.

  4. The Radial Distribution of Asymptotic Giant Branch Stars in Nearby Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Mitchell, Mallory B.; McQuinn, Kristen B.; Boyer, Martha L.; Skillman, Evan D.; Gehrz, Robert D.; Sloan, Greg; McDonald, Iain; Groenewegen, Martin

    2015-01-01

    Asymptotic giant branch (AGB) stars are evolved stars that can experience repeated episodes of mass loss and dust production. As such, they are drivers of galactic chemical enrichment and evolution. While AGB populations have been imaged in many nearby galaxies at optical wavelengths, optical imaging can miss up to 50% of this population due to extinction. Not only is a significant population of AGB stars unidentified in optical surveys, it also is unclear whether younger (and more massive) AGB stars are preferentially obscured. Thus, the distribution, radial profile, and, potentially, age gradient of this important class of stars is not well-constrained in galaxies. The DUST in Nearby Galaxies with Spitzer (DUSTiNGS) survey is a 3.6 and 4.5 μm IRAC imaging survey from the post-cryogen Spitzer mission designed to catalog the evolved stars in 50 nearby dwarf galaxies and identify the most luminous, variable AGB stars. The resulting catalog of the resolved stellar populations at infrared wavelengths provides the means to trace the spatial distribution of evolved stars in the host galaxies. In this study, we use the DUSTiNGS dataset to create radial stellar profiles in nine of the DUSTiNGS sample. We compare the radial distribution of the total evolved stellar populations to the distribution of both the intermediate aged AGB stars and the optically identified, older red giant branch (RGB) stars from Hubble Space Telescope archival images. Additionally, we derive elliptical parameters for seven of the systems from the infrared data and compare these to parameters previously derived from optical data.

  5. Mixing length and opacity effects - Deep convective envelopes on the asymptotic giant branch

    NASA Astrophysics Data System (ADS)

    Sackmann, I.-Juliana; Boothroyd, Arnold I.

    1991-01-01

    We constructed detailed envelopes appropriate to stars on the asymptotic giant branch (AGB) for a wide range of mixing length parameter values alpha, considering different opacities, stellar masses, luminosities, and chemical compositions. Due to the molecular opacities present in the new LAOL opacity tables, a given AGB effective temperature Te requires a mixing length parameter α more than twice as large as that necessary with the older Cox and Stewart opacities. For any set of molecular opacity tables, authors should normalize their value for α by matching observations of the Sun (radius and luminosity at the solar age) or by matching the observed positions of the lower main sequence and red giant branch in the H-R diagram. (For our LAOL opacities, our normalized value turned out to be α ≍ 2.1.) Although this normalization of the mixing length results in a solar convective envelope essentially independent of molecular opacities, this is not true on the AGB: different opacities result in different conditions at the base of the convective envelope on the AGB, even after this normalization. Reliable molecular opacities are imperative for stellar models on the AGB. The temperature TCE at the base of the convective envelope is strongly dependent on the envelope mass and on the luminosity, ranging between 105 K and 107 K for our normalized value of α ≍ 2.1: hot-bottom envelope burning seems not to be totally out of reach. The effect of the chemical composition on TCE is surprisingly small: changes in helium abundance Y have a completely negligible effect, and even a large change in metallicity from Z = 0.02 to 0.001 increases TCE by only a factor of 2. On the AGB, we find that Te ∝ α1/2and R ∝ 1/α.

  6. Evolution and nucleosynthesis of asymptotic giant branch stellar models of low metallicity

    SciTech Connect

    Fishlock, Cherie K.; Karakas, Amanda I.; Yong, David; Lugaro, Maria E-mail: amanda.karakas@anu.edu.au E-mail: maria.lugaro@monash.edu

    2014-12-10

    We present stellar evolutionary tracks and nucleosynthetic predictions for a grid of stellar models of low- and intermediate-mass asymptotic giant branch (AGB) stars at Z = 0.001 ([Fe/H] =–1.2). The models cover an initial mass range from 1 M {sub ☉} to 7 M {sub ☉}. Final surface abundances and stellar yields are calculated for all elements from hydrogen to bismuth as well as isotopes up to the iron group. We present the first study of neutron-capture nucleosynthesis in intermediate-mass AGB models, including a super-AGB model, of [Fe/H] = –1.2. We examine in detail a low-mass AGB model of 2 M {sub ☉} where the {sup 13}C(α,n){sup 16}O reaction is the main source of neutrons. We also examine an intermediate-mass AGB model of 5 M {sub ☉} where intershell temperatures are high enough to activate the {sup 22}Ne neutron source, which produces high neutron densities up to ∼10{sup 14} n cm{sup –3}. Hot bottom burning is activated in models with M ≥ 3 M {sub ☉}. With the 3 M {sub ☉} model, we investigate the effect of varying the extent in mass of the region where protons are mixed from the envelope into the intershell at the deepest extent of each third dredge-up. We compare the results of the low-mass models to three post-AGB stars with a metallicity of [Fe/H] ≅ – 1.2. The composition is a good match to the predicted neutron-capture abundances except for Pb and we confirm that the observed Pb abundances are lower than what is calculated by AGB models.

  7. A BOUND ON THE LIGHT EMITTED DURING THE THERMALLY PULSING ASYMPTOTIC GIANT BRANCH PHASE

    SciTech Connect

    Bird, Jonathan C.; Pinsonneault, Marc H. E-mail: pinsono@astronomy.ohio-state.edu

    2011-06-01

    The integrated luminosity of the thermally pulsing asymptotic giant branch (TP-AGB) phase is a major uncertainty in stellar population synthesis models. We revise the white dwarf initial-final mass relation (IFMR), incorporating the latest composition and distance measurements for several clusters. Using this IFMR and stellar interiors models, we demonstrate that a significant fraction of the core mass growth for intermediate (1.5 < M{sub sun} < 6) mass stars must take place during the TP-AGB phase. This conclusion holds using models both with and without convective overshoot. We find evidence that the peak fractional core mass contribution for TP-AGB stars is {approx}20% and occurs for stars between 2 M{sub sun} and 3.5 M{sub sun}. Using a simple fuel consumption argument we couple this core mass increase to a lower limit on the TP-AGB phase energy output. We demonstrate that the current TP-AGB models of Pietrinferni et al. and Bertelli et al. systematically grow the core less than we require while the latter predict sufficient integrated light. Our calculated lower bound, coupled with chemical evolution constraints, may provide an upper limit to the integrated luminosity of stars in the TP-AGB phase. Alternatively, a robust measurement of the emitted light in this phase and our constraints could set strong constraints on helium enrichment from TP-AGB stars. We estimate the yields predicted by current models as a function of initial mass. Implications for stellar population studies and prospects for improvements are discussed.

  8. Lost and Found: Evidence of Second-generation Stars Along the Asymptotic Giant Branch of the Globular Cluster NGC 6752

    NASA Astrophysics Data System (ADS)

    Lapenna, E.; Lardo, C.; Mucciarelli, A.; Salaris, M.; Ferraro, F. R.; Lanzoni, B.; Massari, D.; Stetson, P. B.; Cassisi, S.; Savino, A.

    2016-07-01

    We derived chemical abundances for C, N, O, Na, Mg, and Al in 20 asymptotic giant branch (AGB) stars in the globular cluster (GC) NGC 6752. All these elements (but Mg) show intrinsic star-to-star variations and statistically significant correlations or anticorrelations analogous to those commonly observed in red giant stars of GCs hosting multiple populations. This demonstrates that, at odds with previous findings, both first- and second-generation (SG) stars populate the AGB of NGC 6752. The comparison with the Na abundances of red giant branch stars in the same cluster reveals that SG stars (with mild Na and He enrichment) do reach the AGB phase. The only objects that are not observed along the AGB of NGC 6752 are stars with extreme Na enhancement. This is also consistent with standard stellar evolution models, showing that highly Na and He enriched stars populate the bluest portion of the horizontal branch and, because of their low stellar masses, evolve directly to the white dwarf cooling sequence, skipping the AGB phase. Based on observations collected at the ESO-VLT under the program 095.D-0320(A).

  9. Evolution and explosion of the most massive asymptotic giant branch star

    SciTech Connect

    Takahashi, Koh; Umeda, Hideyuki; Yoshida, Takashi

    2014-05-02

    The most massive asymptotic giant branch (AGB) stars can form a critical mass of ONe core at its center. The collapse of such a critical ONe core may end up as an Electron Capture Supernova (ECSN). We have accomplished a progenitor calculation for ECSN for the first time in more than two decades and have updated a pre-explosion structure for this model. Some details for ONe core formation and important mechanisms for the core contraction are shown. We discuss how the envelope mass loss affects the predicted existence of ECSN, and what physics is needed to model for a plausible structure of ECSN progenitor.

  10. Hot Bottom Burning in Asymptotic Giant Branch Stars and the Turbulent Convection Model

    NASA Astrophysics Data System (ADS)

    D'Antona, Francesca; Mazzitelli, Italo

    1996-10-01

    We investigate the effect of two different local turbulent convection models on the structure of intermediate-mass stars (IMSs, 3.5 Msun ≤ M ≤7 Msun) in the asymptotic giant branch (AGB) phase where, according to observations, they should experience hot bottom burning (HBB). Evolutionary models adopting either the mixing length theory (MLT) or the Canuto & Mazzitelli (CM) description of stellar convection are discussed. It is found that, while the MLT structures require some degree of tuning to achieve, at the bottom of the convective envelope, the large temperatures required for HBB, the CM structures spontaneously achieve these conditions. Since the observational evidence for HBB (existence of a class of very luminous, lithium-rich AGB stars in the Magellanic Clouds showing low 12C/13C ratios) is quite compelling, the above result provides a further, successful test for the CM convective model, in stellar conditions far from solar. With the aid of the CM model, we then explore a number of problems related to the late evolution of this class of objects, and give first results for (1) the luminosity evolution of IMSs in the AGB phase (core mass-luminosity relation and luminosity range in which HBB occurs) for Population I and Population II structures, (2) the minimum core mass for semidegenerate carbon ignition (˜1.05 Msun), (3) the relation between initial mass and final white dwarf (WD) mass (also based on some observational evidences about the upper AGB stars), and (4) the expected mass function of massive WDs. Confirmation of the theoretical framework could arise from an observational test: the luminosity function of AGB stars is expected to show a gap at Mbol ˜ -6, which would distinguish between the low-luminosity regime, in which AGBs become carbon stars, and the upper luminosities, at which they undergo HBB, have very low 12C/13C ratios, and become lithium rich.

  11. WIDE BINARY EFFECTS ON ASYMMETRIES IN ASYMPTOTIC GIANT BRANCH CIRCUMSTELLAR ENVELOPES

    SciTech Connect

    Kim, Hyosun; Taam, Ronald E. E-mail: r-taam@northwestern.edu

    2012-11-01

    Observations of increasingly higher spatial resolution reveal the existence of asymmetries in the circumstellar envelopes of a small fraction of asymptotic giant branch (AGB) stars. Although there is no general consensus for their origin, a binary companion star may be responsible. Within this framework, we investigate the gravitational effects associated with a sufficiently wide binary system, where Roche lobe overflow is unimportant, on the outflowing envelopes of AGB stars using three-dimensional hydrodynamic simulations. The effects due to individual binary components are separately studied, enabling the investigation of the stellar and circumstellar characteristics in detail. The reflex motion of the AGB star alters the wind velocity distribution, thereby determining the overall shape of the outflowing envelope. On the other hand, the interaction of the companion with the envelope produces a gravitational wake, which exhibits a vertically thinner shape. The two patterns overlap and form clumpy structures. To illustrate the diversity of shapes, we present the numerical results as a function of inclination angle. Not only is spiral structure produced by the binary interaction, but arc patterns are also found that represent the former structure when viewed at different inclinations. The arcs reveal a systematic shift of their centers of curvature for cases when the orbital speed of the AGB star is comparable to its wind speed. They take on the shape of a peanut for inclinations nearly edge-on. In the limit of slow orbital motion of the AGB star relative to the wind speed, the arc pattern becomes nearly spherically symmetric. We find that the aspect ratio of the overall oblate shape of the pattern is an important diagnostic probe of the binary as it can be used to constrain the orbital velocity of the AGB star, and moreover, the binary mass ratio.

  12. A Spitzer Space Telescope Survey of Extreme Asymptotic Giant Branch Stars in M32

    NASA Technical Reports Server (NTRS)

    Jones, O.C.; McDonald, I.; Rich, R.M.; Kemper, F.; Boyer, M.L.; Zijlstra, A.A.; Bendo, G.J.

    2014-01-01

    We investigate the population of cool, evolved stars in the Local Group dwarf elliptical galaxy M32, using Infrared Array Camera observations from the Spitzer Space Telescope. We construct deep mid-infrared colour-magnitude diagrams for the resolved stellar populations within 3.5 arcminutes of M32's centre, and identify those stars that exhibit infrared excess. Our data is dominated by a population of luminous, dustproducing stars on the asymptotic giant branch (AGB) and extend to approximately 3 magnitudes below the AGB tip. We detect for the first time a sizeable population of 'extreme' AGB stars, highly enshrouded by circumstellar dust and likely completely obscured at optical wavelengths. The total dust-injection rate from the extreme AGB candidates is measured to be 7.5 x 10 (sup -7) solar masses per year, corresponding to a gas mass-loss rate of 1.5 x 10 (sup -4) solar masses per year. These extreme stars may be indicative of an extended star-formation epoch between 0.2 and 5 billion years ago.

  13. Infrared spectroscopy of asymptotic giant branch stars in the Galactic bulge

    NASA Astrophysics Data System (ADS)

    Golriz, S. S.; Blommaert, J. A. D. L.; Vanhollebeke, E.; Groenewegen, M. A. T.; Habing, H. J.; Kemper, F.; Schultheis, M.; Tielens, A. G. G. M.; Waters, L. B. F. M.; Wood, P. R.; Cami, J.

    2014-10-01

    We have selected a homogeneous sample of asymptotic giant branch (AGB) stars in the Galactic bulge population from the ISOGAL survey. Our target stars cover a wide range of mass-loss rates (˜10-8-10-4 M⊙ yr-1) and differ primarily by their age on the AGB. This homogeneous sample is thus ideally suited to study the dust formation process as a function of age on the AGB. We observed our sample with Spitzer-Infrared Spectrograph, and studied the overall properties of the infrared spectra of these targets. The analysis is complicated by the presence of strong and variable background emission, and the extracted infrared AGB star spectra are affected by interstellar extinction. Several stars in our sample have no detectable dust emission, and we used these `naked stars' to characterize the stellar and molecular contributions to the infrared spectra of our target stars. The resulting dust spectra of our targets do indeed show significant variety in their spectral appearance, pointing to differing dust compositions for the targets. We classify the spectra based on the shape of their 10-μm emission following the scheme by Sloan & Price. We find that the early silicate emission classes associated with oxide dust are generally under-represented in our sample due to extinction effects. We also find a weak 13-μm dust feature in two of our otherwise naked star spectra, suggesting that the carrier of this feature could potentially be the first condensate in the sequence of dust condensation.

  14. THE INCIDENCE OF NON-SPHERICAL CIRCUMSTELLAR ENVELOPES IN ASYMPTOTIC GIANT BRANCH STARS

    SciTech Connect

    Politano, Michael; Taam, Ronald E.

    2011-11-01

    The relative occurrence of asymmetric structures in the circumstellar envelopes (CSEs) of asymptotic giant branch (AGB) stars in detached binary star systems is studied based on a population synthesis method. The effects of envelope shaping by the gravitational interaction of the companion on an outflowing stellar wind are incorporated using previously derived empirical fits to numerical simulations. It is shown that significant asymmetries in the CSE, characterized by a ratio of the density in the equatorial direction relative to the polar direction, can exceed 10 for AGB stars characterized by luminosities in the range of 1000-10, 000 L{sub sun} in systems with orbital separations of 3-30 AU and mass ratios of 0.25-1. The incidence of such systems relative to a present-day field population of AGB stars (single + binary) is estimated to be 1%-6%, depending upon input parameter choices. For more modest density contrasts exceeding a factor of two, the incidence increases to 4%-15%. With the advent of future high-resolution molecular line studies of CSEs with the Atacama Large Millimeter Array, it is anticipated that the number of AGB stars exhibiting detectable asymmetries will significantly increase.

  15. The transition from carbon dust to silicate production in low-metallicity asymptotic giant branch and super-asymptotic giant branch stars

    NASA Astrophysics Data System (ADS)

    Ventura, P.; di Criscienzo, M.; Schneider, R.; Carini, R.; Valiante, R.; D'Antona, F.; Gallerani, S.; Maiolino, R.; Tornambé, A.

    2012-02-01

    We compute the mass and composition of dust produced by stars with masses in the range ? and with a metallicity of Z= 0.001 during their asymptotic giant branch (AGB) and super-AGB phases. Stellar evolution is followed from the pre-main-sequence phase using the code ATON which provides, at each time-step, the thermodynamics and the chemical structure of the wind. We use a simple model to describe the growth of the dust grains under the hypothesis of a time-independent, spherically symmetric stellar wind. Although part of the modelling which describes the stellar outflow is not completely realistic, this approach allows a straight comparison with results based on similar assumptions present in the literature, and thus can be used as an indication of the uncertainties affecting the theoretical investigations focused on the dust formation process in the surroundings of AGB stars. We find that the total mass of dust injected by AGB stars in the interstellar medium does not increase monotonically with stellar mass and ranges between a minimum of ? for the 1.5-? stellar model up to ?, for the 6-? case. Dust composition depends on the stellar mass: low-mass stars (?) produce carbon-rich dust, whereas more massive stars, experiencing Hot Bottom Burning, never reach the C-star stage, and produce silicates and iron. This is in partial disagreement with previous investigations in the literature, which are based on synthetic AGB models and predict that, when the initial metallicity is Z= 0.001, carbon-rich dust is formed at all stellar masses. The differences are due to the different modelling of turbulent convection in the super-adiabaticity regime. Also in this case, like for other physical features of the AGB, the treatment of super-adiabatic convection shows up as the most relevant issue affecting the dust formation process. We also investigate super-AGB stars with masses in the range ? that evolve over an ONe core. Due to a favourable combination of mass-loss and Hot

  16. THE S{sup 4}G PERSPECTIVE ON CIRCUMSTELLAR DUST EXTINCTION OF ASYMPTOTIC GIANT BRANCH STARS IN M100

    SciTech Connect

    Meidt, Sharon E.; Schinnerer, Eva; Holwerda, Benne; Ho, Luis C.; Madore, Barry F.; Sheth, Kartik; Menendez-Delmestre, Karin; Seibert, Mark; Knapen, Johan H.; Bosma, Albert; Athanassoula, E.; Hinz, Joannah L.; Regan, Michael; De Paz, Armando Gil; Mizusawa, Trisha; Gadotti, Dimitri A.; Laurikainen, Eija; Salo, Heikki; and others

    2012-04-01

    We examine the effect of circumstellar dust extinction on the near-IR (NIR) contribution of asymptotic giant branch (AGB) stars in intermediate-age clusters throughout the disk of M100. For our sample of 17 AGB-dominated clusters we extract optical-to-mid-IR spectral energy distributions (SEDs) and find that NIR brightness is coupled to the mid-IR dust emission in such a way that a significant reduction of AGB light, of up to 1 mag in the K band, follows from extinction by the dust shell formed during this stage. Since the dust optical depth varies with AGB chemistry (C-rich or O-rich), our results suggest that the contribution of AGB stars to the flux from their host clusters will be closely linked to the metallicity and the progenitor mass of the AGB star, to which dust chemistry and mass-loss rate are sensitive. Our sample of clusters-each the analogue of a {approx}1 Gyr old post-starburst galaxy-has implications within the context of mass and age estimation via SED modeling at high-z: we find that the average {approx}0.5 mag extinction estimated here may be sufficient to reduce the AGB contribution in the (rest-frame) K band from {approx}70%, as predicted in the latest generation of synthesis models, to {approx}35%. Our technique for selecting AGB-dominated clusters in nearby galaxies promises to be effective for discriminating the uncertainties associated with AGB stars in intermediate-age populations that plague age and mass estimation in high-z galaxies.

  17. THE INSIDIOUS BOOSTING OF THERMALLY PULSING ASYMPTOTIC GIANT BRANCH STARS IN INTERMEDIATE-AGE MAGELLANIC CLOUD CLUSTERS

    SciTech Connect

    Girardi, Léo; Marigo, Paola; Bressan, Alessandro; Rosenfield, Philip

    2013-11-10

    In the recent controversy about the role of thermally pulsing asymptotic giant branch (TP-AGB) stars in evolutionary population synthesis (EPS) models of galaxies, one particular aspect is puzzling: TP-AGB models aimed at reproducing the lifetimes and integrated fluxes of the TP-AGB phase in Magellanic Cloud (MC) clusters, when incorporated into EPS models, are found to overestimate, to various extents, the TP-AGB contribution in resolved star counts and integrated spectra of galaxies. In this paper, we call attention to a particular evolutionary aspect, linked to the physics of stellar interiors, that in all probability is the main cause of this conundrum. As soon as stellar populations intercept the ages at which red giant branch stars first appear, a sudden and abrupt change in the lifetime of the core He-burning phase causes a temporary 'boost' in the production rate of subsequent evolutionary phases, including the TP-AGB. For a timespan of about 0.1 Gyr, triple TP-AGB branches develop at slightly different initial masses, causing their frequency and contribution to the integrated luminosity of the stellar population to increase by a factor of ∼2. The boost occurs for turn-off masses of ∼1.75 M{sub ☉}, just in the proximity of the expected peak in the TP-AGB lifetimes (for MC metallicities), and for ages of ∼1.6 Gyr. Coincidently, this relatively narrow age interval happens to contain the few very massive MC clusters that host most of the TP-AGB stars used to constrain stellar evolution and EPS models. This concomitance makes the AGB-boosting particularly insidious in the context of present EPS models. As we discuss in this paper, the identification of this evolutionary effect brings about three main consequences. First, we claim that present estimates of the TP-AGB contribution to the integrated light of galaxies derived from MC clusters are biased toward too large values. Second, the relative TP-AGB contribution of single-burst populations falling in

  18. New models for the evolution of post-asymptotic giant branch stars and central stars of planetary nebulae

    NASA Astrophysics Data System (ADS)

    Miller Bertolami, Marcelo Miguel

    2016-04-01

    Context. The post-asymptotic giant branch (AGB) phase is arguably one of the least understood phases of the evolution of low- and intermediate- mass stars. The two grids of models presently available are based on outdated micro- and macrophysics and do not agree with each other. Studies of the central stars of planetary nebulae (CSPNe) and post-AGB stars in different stellar populations point to significant discrepancies with the theoretical predictions of post-AGB models. Aims: We study the timescales of post-AGB and CSPNe in the context of our present understanding of the micro- and macrophysics of stars. We want to assess whether new post-AGB models, based on the latter improvements in TP-AGB modeling, can help us to understand the discrepancies between observation and theory and within theory itself. In addition, we aim to understand the impact of the previous AGB evolution for post-AGB phases. Methods: We computed a grid of post-AGB full evolutionary sequences that include all previous evolutionary stages from the zero age main sequence to the white dwarf phase. We computed models for initial masses between 0.8 and 4 M⊙ and for a wide range of initial metallicities (Z0 = 0.02, 0.01, 0.001, 0.0001). This allowed us to provide post-AGB timescales and properties for H-burning post-AGB objects with masses in the relevant range for the formation of planetary nebulae (~0.5-0.8 M⊙). We included an updated treatment of the constitutive microphysics and included an updated description of the mixing processes and winds that play a key role during the thermal pulses (TP) on the AGB phase. Results: We present a new grid of models for post-AGB stars that take into account the improvements in the modeling of AGB stars in recent decades. These new models are particularly suited to be inputs in studies of the formation of planetary nebulae and for the determination of the properties of CSPNe from their observational parameters. We find post-AGB timescales that are at

  19. STRONG VARIABLE ULTRAVIOLET EMISSION FROM Y GEM: ACCRETION ACTIVITY IN AN ASYMPTOTIC GIANT BRANCH STAR WITH A BINARY COMPANION?

    SciTech Connect

    Sahai, Raghvendra; Neill, James D.; Gil de Paz, Armando; Sanchez Contreras, Carmen

    2011-10-20

    Binarity is believed to dramatically affect the history and geometry of mass loss in asymptotic giant branch (AGB) and post-AGB stars, but observational evidence of binarity is sorely lacking. As part of a project to look for hot binary companions to cool AGB stars using the Galaxy Evolution Explorer archive, we have discovered a late-M star, Y Gem, to be a source of strong and variable UV emission. Y Gem is a prime example of the success of our technique of UV imaging of AGB stars in order to search for binary companions. Y Gem's large and variable UV flux makes it one of the most prominent examples of a late-AGB star with a mass accreting binary companion. The UV emission is most likely due to emission associated with accretion activity and a disk around a main-sequence companion star. The physical mechanism generating the UV emission is extremely energetic, with an integrated luminosity of a few x L{sub sun} at its peak. We also find weak CO J = 2-1 emission from Y Gem with a very narrow line profile (FWHM of 3.4 km s{sup -1}). Such a narrow line is unlikely to arise in an outflow and is consistent with emission from an orbiting, molecular reservoir of radius 300 AU. Y Gem may be the progenitor of the class of post-AGB stars which are binaries and possess disks but no outflows.

  20. A test for asymptotic giant branch evolution theories: planetary nebulae in the Large Magellanic Cloud

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

    We used a new generation of asymptotic giant branch (AGB) stellar models that include dust formation in the stellar winds to find the links between evolutionary models and the observed properties of a homogeneous sample of Large Magellanic Cloud (LMC) planetary nebulae (PNe). Comparison between the evolutionary yields of elements such as CNO and the corresponding observed chemical abundances is a powerful tool to shed light on evolutionary processes such as hot bottom burning (HBB) and third dredge-up (TDU). We found that the occurrence of HBB is needed to interpret the nitrogen-enriched (log (N/H) + 12 > 8) PNe. In particular, N-rich PNe with the lowest carbon content are nicely reproduced by AGB models of mass M ≥ 6 M⊙, whose surface chemistry reflects the pure effects of HBB. PNe with log (N/H) + 12 < 7.5 correspond to ejecta of stars that have not experienced HBB, with initial mass below ˜3 M⊙. Some of these stars show very large carbon abundances, owing to the many TDU episodes experienced. We found from our LMC PN sample that there is a threshold to the amount of carbon accumulated at AGB surfaces, log (C/H) + 12 < 9. Confirmation of this constraint would indicate that, after the C-star stage is reached, AGBs experience only a few thermal pulses, which suggests a rapid loss of the external mantle, probably owing to the effects of radiation pressure on carbonaceous dust particles present in the circumstellar envelope. The implications of these findings for AGB evolution theories and the need to extend the PN sample currently available are discussed.

  1. The Local Group Galaxy IC 1613 and its asymptotic giant branch variables

    NASA Astrophysics Data System (ADS)

    Menzies, John W.; Whitelock, Patricia A.; Feast, Michael W.

    2015-09-01

    JHKS photometry is presented from a 3-yr survey of the central regions of the Local Group dwarf irregular galaxy IC 1613. The morphologies of the colour-magnitude and colour-colour diagrams are discussed with particular reference to the supergiants and M- and C-type asymptotic giant branch (AGB) stars. Mean JHKS magnitudes, amplitudes and periods are given for five O-rich and nine C-rich Mira variables for which bolometric magnitudes are also estimated. A distance of 750 kpc ((m - M)0 = 24.37 ± 0.08 mag) is derived for IC 1613 by fitting a period-luminosity (PL) relation to the C-rich Miras. This is in agreement with values from the literature. The AGB stars exhibit a range of ages. A comparison with theoretical isochrones suggests that four luminous O-rich Miras are as young as 2 × 108 yr. One of these has a lithium absorption line in its spectrum, demonstrating that it is undergoing hot bottom burning (HBB). This supports the idea that HBB is the cause of the high luminosity of these AGB stars, which puts them above the fundamental PL relation. Further studies of similar stars, selected from their positions in the PL diagram, could provide insight into HBB. A much fainter, presumed O-rich, Mira is similar to those found in Galactic globular clusters. The C Miras are of intermediate age. The O-rich variables are not all recognized as O-rich, or even as AGB stars, on the basis of their J - KS colour. It is important to appreciate this when using near-infrared surveys to classify AGB stars in more distant galaxies.

  2. Near-infrared properties of asymptotic giant branch stars in nearby dwarf elliptical galaxy NGC 205

    NASA Astrophysics Data System (ADS)

    Jung, M. Y.; Ko, J.; Kim, J.-W.; Chun, S.-H.; Kim, H.-I.; Sohn, Y.-J.

    2012-07-01

    Aims: We investigated the distribution of resolved asymptotic giant branch (AGB) stars over a much larger area than covered by previous near-infrared studies in the nearby dwarf elliptical galaxy NGC 205. Methods: Using data obtained with the WIRCam near-infrared imager of the CFHT, we selected the AGB stars in the JHKs color - magnitude diagrams, and separated the C stars from M-giant stars in the JHKs color - color diagram. Results: We identified 1,550 C stars in NGC 205 with a mean absolute magnitude of ⟨ MKs ⟩ = -7.49 ± 0.54, and colors of ⟨ (J - Ks)0 ⟩ = 1.81 ± 0.41 and ⟨ (H - Ks)0 ⟩ = 0.76 ± 0.24. The ratio of C stars to M-giant stars was estimated to be 0.15 ± 0.01 in NGC 205, and the local C/M ratios for the southern region are somewhat lower than those for the northern region. The (J - Ks) color distributions of AGB stars contain the main peak of the M-giant stars and the red tail of the C stars. A comparison of the theoretical isochrone models with the observed color distribution indicates that most of the bright M-giant stars in NGC 205 were formed at log (tyr) ~ 9.0-9.7. The logarithmic slope of the MKs luminosity function for M-giant stars was estimated to be 0.84 ± 0.01, which is comparable with dwarf elliptical galaxies NGC 147 and NGC 185. Furthermore, we found that the logarithmic slopes of the MKs luminosity function for C and M-giant stars are different to places, implying a different star formation history within NGC 205. The bolometric luminosity function for M-giant stars extends to Mbol = -6.0 mag, and that for C stars spans -5.6 < Mbol < -3.0. The bolometric luminosity function of C stars is unlikely to be a Gaussian distribution and the mean bolometric magnitude of C stars is estimated to be Mbol = -4.24 ± 0.55, which is consistent with our results for dwarf elliptical galaxies NGC 147 and NGC 185. Based on observations carried out at the Canada-France-Hawaii Telescope, operated by the National Research Council of Canada

  3. Clear Evidence for the Presence of Second-generation Asymptotic Giant Branch Stars in Metal-poor Galactic Globular Clusters

    NASA Astrophysics Data System (ADS)

    García-Hernández, D. A.; Mészáros, Sz.; Monelli, M.; Cassisi, S.; Stetson, P. B.; Zamora, O.; Shetrone, M.; Lucatello, S.

    2015-12-01

    Galactic globular clusters (GCs) are known to host multiple stellar populations: a first generation (FG) with a chemical pattern typical of halo field stars and a second generation (SG) enriched in Na and Al and depleted in O and Mg. Both stellar generations are found at different evolutionary stages (e.g., the main-sequence turnoff, the subgiant branch, and the red giant branch (RGB)). The non detection of SG asymptotic giant branch (AGB) stars in several metal-poor ([Fe/H] < -1) GCs suggests that not all SG stars ascend the AGB phase, and that failed AGB stars may be very common in metal-poor GCs. This observation represents a serious problem for stellar evolution and GC formation/evolution theories. We report fourteen SG-AGB stars in four metal-poor GCs (M13, M5, M3, and M2) with different observational properties: horizontal branch (HB) morphology, metallicity, and age. By combining the H-band Al abundances obtained by the Apache Point Observatory Galactic Evolution Experiment survey with ground-based optical photometry, we identify SG Al-rich AGB stars in these four GCs and show that Al-rich RGB/AGB GC stars should be Na-rich. Our observations provide strong support for present, standard stellar models, i.e., without including a strong mass-loss efficiency, for low-mass HB stars. In fact, current empirical evidence is in agreement with the predicted distribution of FG and SG stars during the He-burning stages based on these standard stellar models.

  4. FLUORINE IN THE SOLAR NEIGHBORHOOD: IS IT ALL PRODUCED IN ASYMPTOTIC GIANT BRANCH STARS?

    SciTech Connect

    Jönsson, H.; Ryde, N.; Harper, G. M.; Richter, M. J.; Hinkle, K. H.

    2014-07-10

    The origin of ''cosmic'' fluorine is uncertain, but there are three proposed production sites/mechanisms for the origin: asymptotic giant branch (AGB) stars, ν nucleosynthesis in Type II supernovae, and/or the winds of Wolf-Rayet stars. The relative importance of these production sites has not been established even for the solar neighborhood, leading to uncertainties in stellar evolution models of these stars as well as uncertainties in the chemical evolution models of stellar populations. We determine the fluorine and oxygen abundances in seven bright, nearby giants with well determined stellar parameters. We use the 2.3 μm vibrational-rotational HF line and explore a pure rotational HF line at 12.2 μm. The latter has never been used before for an abundance analysis. To be able to do this, we have calculated a line list for pure rotational HF lines. We find that the abundances derived from the two diagnostics agree. Our derived abundances are well reproduced by chemical evolution models including only fluorine production in AGB stars and, therefore, we draw the conclusion that this might be the main production site of fluorine in the solar neighborhood. Furthermore, we highlight the advantages of using the 12 μm HF lines to determine the possible contribution of the ν process to the fluorine budget at low metallicities where the difference between models including and excluding this process is dramatic.

  5. Barium Isotopic Composition of Mainstream Silicon Carbides from Murchison: Constraints for s-process Nucleosynthesis in Asymptotic Giant Branch Stars

    NASA Astrophysics Data System (ADS)

    Liu, Nan; Savina, Michael R.; Davis, Andrew M.; Gallino, Roberto; Straniero, Oscar; Gyngard, Frank; Pellin, Michael J.; Willingham, David G.; Dauphas, Nicolas; Pignatari, Marco; Bisterzo, Sara; Cristallo, Sergio; Herwig, Falk

    2014-05-01

    We present barium, carbon, and silicon isotopic compositions of 38 acid-cleaned presolar SiC grains from Murchison. Comparison with previous data shows that acid washing is highly effective in removing barium contamination. Strong depletions in δ(138Ba/136Ba) values are found, down to -400‰, which can only be modeled with a flatter 13C profile within the 13C pocket than is normally used. The dependence of δ(138Ba/136Ba) predictions on the distribution of 13C within the pocket in asymptotic giant branch (AGB) models allows us to probe the 13C profile within the 13C pocket and the pocket mass in AGB stars. In addition, we provide constraints on the 22Ne(α, n)25Mg rate in the stellar temperature regime relevant to AGB stars, based on δ(134Ba/136Ba) values of mainstream grains. We found two nominally mainstream grains with strongly negative δ(134Ba/136Ba) values that cannot be explained by any of the current AGB model calculations. Instead, such negative values are consistent with the intermediate neutron capture process (i process), which is activated by the very late thermal pulse during the post-AGB phase and characterized by a neutron density much higher than the s process. These two grains may have condensed around post-AGB stars. Finally, we report abundances of two p-process isotopes, 130Ba and 132Ba, in single SiC grains. These isotopes are destroyed in the s process in AGB stars. By comparing their abundances with respect to that of 135Ba, we conclude that there is no measurable decay of 135Cs (t 1/2 = 2.3 Ma) to 135Ba in individual SiC grains, indicating condensation of barium, but not cesium into SiC grains before 135Cs decayed.

  6. The impact of thermally pulsing asymptotic giant branch stars on hierarchical galaxy formation models

    NASA Astrophysics Data System (ADS)

    Tonini, Chiara; Maraston, Claudia; Devriendt, Julien; Thomas, Daniel; Silk, Joseph

    2009-06-01

    The spectro-photometric properties of galaxies in galaxy formation models are obtained by combining the predicted history of star formation and mass accretion with the physics of stellar evolution through stellar population models. In the recent literature, significant differences have emerged regarding the implementation of the thermally pulsing asymptotic giant branch phase of stellar evolution. The emission in the TP-AGB phase dominates the bolometric and near-IR spectrum of intermediate-age (~1Gyr) stellar populations, hence it is crucial for the correct modelling of the galaxy luminosities and colours. In this paper, for the first time, we incorporate a full prescription of the TP-AGB phase in a semi-analytic model of galaxy formation. We find that the inclusion of the TP-AGB in the model spectra dramatically alters the predicted colour-magnitude relation and its evolution with redshift. When the TP-AGB phase is active, the rest-frame V - K galaxy colours are redder by almost 2 mag in the redshift range z ~ 2-3 and by 1 mag at z ~ 1. Very red colours are produced in disc galaxies, so that the V - K colour distributions of disc and spheroids are virtually undistinguishable at low redshifts. We also find that the galaxy K-band emission is more than 1 mag higher in the range z ~ 1-3. This may alleviate the difficulties met by the hierarchical clustering scenario in predicting the red galaxy population at high redshifts. The comparison between simulations and observations has to be revisited in the light of our results.

  7. Hot bottom burning in asymptotic giant branch stars and its effect on oxygen isotopic abundances

    NASA Technical Reports Server (NTRS)

    Boothroyd, Arnold I.; Sackmann, I.-JULIANA; Wasserburg, G. J.

    1995-01-01

    A self-consistent calculation of asymptotic giant branch (AGB) evolution was carried out, including nucleosynthesis at the base of the convective envelope (hot bottom burning). Hot bottom burning was found to occur for stars between approximately 4.5 and approximately 7 solar mass, producing envelopes with O-18/O-16 less than or equal to 10(exp -6) and 10(exp -3) approximately less than or equal O-17/O-16 approximately less than or equal to 10(exp -1). The O-17 abundance depends sensitively on the nuclear O-17-destruction rate; this rate is only loosely constrained by the requirement that first and second dredge-up models match O-isotope observations of red giant branch (RGB) stars (Boothroyd, Sackmann, & Wasserburg 1994). In some cases, high mass-loss rates can terminate hot bottom burning before further O-17 enrichment takes place or even before all O-18 is destroyed. These predictions are in accord with the very limited stellar observations of J type carbon stars on the AGB and with some of the circumstellar Al2O3 grains from meteorites. In contrast, precise data from a number of grains and data from most low-mass S and C AGB stars (approximately less than 1.7 solar mass) lie in a region of the O-18/O-16 versus O-17/O-16 diagram that is not accessible by first and second dredge-up or by hot bottom burning. We conclude that for AGB stars, the standard models of stellar evolution are not in accord with these observations. We surmise that an additional mixing mechanism must exist that transports material from the cool bottom of the stellar convective envelope to a depth at which O-18 is destroyed. This 'cool bottom processing' mechanism on the AGB is similar to extra mixing mechanisms proposed to explain the excess C-13 (and depleted C-12) observed in the earlier RGB stage of evolution and the large Li-7 depletion observed in low-mass main-sequence stars.

  8. Post Asymptotic Giant Branch and Central Stars of Planetary Nebulae in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Weston, Simon

    2012-01-01

    Post asymptotic giant branch (post-AGB) stars, central stars of planetary nebulae (CSPNe) and planetary nebulae (PNe) are important phases of stellar evolution as the material they feedback is the seed of subsequent star formation in a galaxy. The majority of low and intermediate mass stars are expected to evolve through these channels, however, it is uncertain how many actually do, and at what rate. The Galactic halo, with its older population, provides a direct test of evolutionary models for low mass stars. Birthrate estimates of PNe are uncertain and worse still, are in contradiction with accepted white dwarf (WD) birthrate estimates. Much of the uncertainty stems from the lack of complete samples and poorly determined distance estimates. New surveys such as the Sloan Digital Sky Survey (SDSS), Galaxy Evolutionary Explorer (GALEX) and the INT Photometric Ha Survey (IPHAS) have discovered many new PNe and have observed the far edges of the Galaxy. Improved methods of determining distances to CSPNe are presented here, using model atmospheres, evolutionary tracks and high resolution reddening maps utilising these revolutionary surveys. Locating the CSPN is non-trivial particularly for evolved PNe, as they are extended with their central star often displaced from the centre of the nebula. Therefore, photometric criteria are required to locate the CSPN in the nebula's field. Synthetic photometry of the CSPNe is derived from spectral energy distributions (SEDs) computed from a grid of model atmospheres covering the parameter range of CSPNe. The SEDs are convolved with filter transmission curves to compute synthetic magnitudes for a given photometric system which are then calibrated with standard stars and WDs. A further project borne out of a search for luminous central stars of faint PNe, resulted in a systematic search for post-AGB stars in the Galactic halo. In this work, new candidate halo post-AGB stars are discovered from a search through the SDSS spectroscopic

  9. Galactic planetary nebulae with precise nebular abundances as a tool to understand the evolution of asymptotic giant branch stars

    NASA Astrophysics Data System (ADS)

    García-Hernández, D. A.; Ventura, P.; Delgado-Inglada, G.; Dell'Agli, F.; Di Criscienzo, M.; Yagüe, A.

    2016-09-01

    We present nucleosynthesis predictions (HeCNOCl) from asymptotic giant branch (AGB) models, with diffusive overshooting from all the convective borders, in the metallicity range Z⊙/4 < Z < 2 Z⊙. They are compared to recent precise nebular abundances in a sample of Galactic planetary nebulae (PNe) that is divided among double-dust chemistry (DC) and oxygen-dust chemistry (OC) according to the infrared dust features. Unlike the similar subsample of Galactic carbon-dust chemistry PNe recently analysed by us, here the individual abundance errors, the higher metallicity spread, and the uncertain dust types/subtypes in some PNe do not allow a clear determination of the AGB progenitor masses (and formation epochs) for both PNe samples; the comparison is thus more focused on a object-by-object basis. The lowest metallicity OC PNe evolve from low-mass (˜1 M⊙) O-rich AGBs, while the higher metallicity ones (all with uncertain dust classifications) display a chemical pattern similar to the DC PNe. In agreement with recent literature, the DC PNe mostly descend from high-mass (M ≥ 3.5 M⊙) solar/supersolar metallicity AGBs that experience hot bottom burning (HBB), but other formation channels in low-mass AGBs like extra mixing, stellar rotation, binary interaction, or He pre-enrichment cannot be disregarded until more accurate C/O ratios would be obtained. Two objects among the DC PNe show the imprint of advanced CNO processing and deep second dredge-up, suggesting progenitors masses close to the limit to evolve as core collapse supernovae (above 6M⊙). Their actual C/O ratio, if confirmed, indicate contamination from the third dredge-up, rejecting the hypothesis that the chemical composition of such high-metallicity massive AGBs is modified exclusively by HBB.

  10. Galactic planetary nebulae with precise nebular abundances as a tool to understand the evolution of asymptotic giant branch stars

    NASA Astrophysics Data System (ADS)

    García-Hernández, D. A.; Ventura, P.; Delgado-Inglada, G.; Dell'Agli, F.; Di Criscienzo, M.; Yagüe, A.

    2016-06-01

    We present nucleosynthesis predictions (HeCNOCl) from asymptotic giant branch (AGB) models, with diffusive overshooting from all the convective borders, in the metallicity range Z⊙/4 < Z < 2Z⊙. They are compared to recent precise nebular abundances in a sample of Galactic planetary nebulae (PNe) that is divided among double-dust chemistry (DC) and oxygen-dust chemistry (OC) according to the infrared dust features. Unlike the similar subsample of Galactic carbon-dust chemistry PNe recently analysed by us, here the individual abundance errors, the higher metallicity spread, and the uncertain dust types/subtypes in some PNe do not allow a clear determination of the AGB progenitor masses (and formation epochs) for both PNe samples; the comparison is thus more focussed on a object-by-object basis. The lowest metallicity OC PNe evolve from low-mass (˜1 M⊙) O-rich AGBs, while the higher metallicity ones (all with uncertain dust classifications) display a chemical pattern similar to the DC PNe. In agreement with recent literature, the DC PNe mostly descend from high-mass (M ≥3.5 M⊙) solar/supersolar metallicity AGBs that experience hot bottom burning (HBB), but other formation channels in low-mass AGBs like extra mixing, stellar rotation, binary interaction, or He pre-enrichment cannot be disregarded until more accurate C/O ratios would be obtained. Two objects among the DC PNe show the imprint of advanced CNO processing and deep second dredge-up, suggesting progenitors masses close to the limit to evolve as core collapse supernovae (above 6~M⊙). Their actual C/O ratio, if confirmed, indicate contamination from the third dredge-up, rejecting the hypothesis that the chemical composition of such high-metallicity massive AGBs is modified exclusively by HBB.

  11. Identification of oxygen-rich late/post-asymptotic giant branch stars and water fountains via maser and infrared criteria

    NASA Astrophysics Data System (ADS)

    Yung, Bosco H. K.; Nakashima, Jun-ichi; Henkel, Christian; Hsia, Chih-Hao

    2016-07-01

    The transitional phase between the asymptotic giant branch (AGB) and post-AGB phases holds the key to our understanding of the late-stage metamorphosis of intermediate-mass stars. In particular, high velocity jets forming during this phase are suggested to contribute significantly to the shaping of planetary nebulae. For oxygen-rich stars, the rare “water fountains (WFs)” have been regarded as representative objects in this phase, and it is important to identify more of them for further studies. Here we briefly report the results of our latest OH and H2O maser surveys in which a new WF candidate (IRAS 19356+0754) was found. We also performed radiative transfer modelling on the spectral energy distributions (SEDs) of all known WFs. It is concluded that WFs might in fact not be the transitional objects, as opposed to previous belief. WFs could be AGB or post-AGB stars with no obvious similarities amongst their SEDs. Further efforts are still needed to improve the identification criteria.

  12. Spitzer-IRS Spectroscopic Studies of Oxygen-Rich Asymptotic Giant Branch Star and Red Supergiant Star Dust Properties

    NASA Astrophysics Data System (ADS)

    Sargent, Benjamin A.; Srinivasan, Sundar; Speck, Angela; Volk, Kevin; Kemper, Ciska; Reach, William T.; Lagadec, Eric; Bernard, Jean-Philippe; McDonald, Iain; Meixner, Margaret

    2015-01-01

    We analyze the dust emission features seen in Spitzer Space Telescope Infrared Spectrograph (IRS) spectra of Oxygen-rich (O-rich) asymptotic giant branch (AGB) and red supergiant (RSG) stars. The spectra come from the Spitzer Legacy program SAGE-Spectroscopy (PI: F. Kemper) and other archival Spitzer-IRS programs. The broad 10 and 20 micron emission features attributed to amorphous dust of silicate composition seen in the spectra show evidence for systematic differences in the centroid of both emission features between O-rich AGB and RSG populations. Radiative transfer modeling using the GRAMS grid of models of AGB and RSG stars suggests that the centroid differences are due to differences in dust properties. We present an update of our investigation of differences in dust composition, size, shape, etc that might be responsible for these spectral differences. We explore how these differences may arise from the different circumstellar environments around RSG and O-rich AGB stars. BAS acknowledges funding from NASA ADAP grant NNX13AD54G.

  13. Comparative Studies of the Dust around Red Supergiant and Oxygen-Rich Asymptotic Giant Branch Stars in the Local Universe

    NASA Astrophysics Data System (ADS)

    Sargent, Benjamin; Srinivasan, Sundar; Speck, Angela K.; Volk, Kevin; Kemper, Ciska; Reach, William; Lagadec, Eric; Bernard, Jean-Philippe; McDonald, Iain; Meixner, Margaret; Sloan, Greg; Jones, Olivia

    2015-08-01

    We analyze the dust emission features seen in Spitzer Space Telescope Infrared Spectrograph (IRS) spectra of red supergiant (RSG) and oxygen-rich asymptotic giant branch (AGB) stars in the Large Magellanic Cloud and Small Magellanic Cloud galaxies and in various Milky Way globular clusters. The spectra come from the Spitzer Legacy program SAGE-Spectroscopy (PI: F. Kemper), the Spitzer program SMC-Spec (PI: G. Sloan), and other archival Spitzer-IRS programs. The broad 10 and 20 μm emission features attributed to amorphous dust of silicate composition seen in the spectra show evidence for systematic differences in the centroid of both emission features between O-rich AGB and RSG populations. Radiative transfer modeling using the GRAMS grid of models of AGB and RSG stars suggests that the centroid differences are due to differences in dust properties. We investigate differences in dust composition, size, shape, etc that might be responsible for these spectral differences. We explore how these differences may arise from the different circumstellar environments around RSG and O-rich AGB stars and assess effects of varying metallicity (LMC versus SMC versus Milky Way globular cluster) and other properties (mass-loss rate, luminosity, etc.) on the dust originating from these stars. BAS acknowledges funding from NASA ADAP grant NNX13AD54G.

  14. How Do Massive Asymptotic Giant Branch Stars Lose All Their Mass?

    NASA Astrophysics Data System (ADS)

    de Vries, B. L.; Blommaert, J. A. D. L.; Waters, L. B. F. M.; Waelkens, C.; Min, M.; Lombaert, R.; Van Winckel, H.

    2015-08-01

    Recent studies have made it increasingly clear that oxygen-rich and massive (≥5 M⊙) asymptotic giant branch (AGB) stars go through only one, short, superwind. Although the superwind was originally introduced for the star to lose enough mass to reach that of a white dwarf, evidence is now building that the superwind lasts too short a time for it to be sufficiently efficient. The integrated mass lost during the whole superwind is not enough to remove the remaining H-rich envelope and terminate the AGB. Studies presented at the conference have shown, from methods based on both gas and dust, that the superwind lasts only ≲1200 years. The analysis of solid-state spectral bands of crystalline olivine (Mg2-2xFe2xSiO4) in the spectra of massive OH/IR stars is a powerful way to determine the extent of the superwind. De Vries, Blommaert, Waters et al. (2014) show that the temperature indicated by the observed 69μm band of crystalline olivine can only be reproduced by models with a geometrically compact superwind (RSW ≲ 2500 AU = 1400 R*). The way by which a star loses its remaining mass after the superwind is unknown. During the conference this problem was discussed and the most likely hypothesis would be a short but very strong phase after the superwind. This hyperwind would have a mass-loss rate of ≳10-3 M⊙/yr.

  15. NON-LOCAL THERMODYNAMICAL EQUILIBRIUM EFFECTS ON THE IRON ABUNDANCE OF ASYMPTOTIC GIANT BRANCH STARS IN 47 TUCANAE

    SciTech Connect

    Lapenna, E.; Mucciarelli, A.; Lanzoni, B.; Ferraro, F. R.; Dalessandro, E.; Massari, D.

    2014-12-20

    We present the iron abundance of 24 asymptotic giant branch (AGB) stars, members of the globular cluster 47 Tucanae, obtained with high-resolution spectra collected with the FEROS spectrograph at the MPG/ESO 2.2 m Telescope. We find that the iron abundances derived from neutral lines (with a mean value [Fe I/H] =–0.94 ± 0.01, σ = 0.08 dex) are systematically lower than those derived from single ionized lines ([Fe II/H] =–0.83 ± 0.01, σ = 0.05 dex). Only the latter are in agreement with those obtained for a sample of red giant branch (RGB) cluster stars, for which the Fe I and Fe II lines provide the same iron abundance. This finding suggests that non-local thermodynamical equilibrium (NLTE) effects driven by overionization mechanisms are present in the atmosphere of AGB stars and significantly affect the Fe I lines while leaving Fe II features unaltered. On the other hand, the very good ionization equilibrium found for RGB stars indicates that these NLTE effects may depend on the evolutionary stage. We discuss the impact of this finding on both the chemical analysis of AGB stars and on the search for evolved blue stragglers.

  16. 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.

  17. 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

  18. Evolution of thermally pulsing asymptotic giant branch stars - I. The COLIBRI code

    NASA Astrophysics Data System (ADS)

    Marigo, Paola; Bressan, Alessandro; Nanni, Ambra; Girardi, Léo; Pumo, Maria Letizia

    2013-09-01

    We present the COLIBRI code for computing the evolution of stars along the thermally pulsing asymptotic giant branch (TP-AGB) phase. Compared to purely synthetic TP-AGB codes, COLIBRI relaxes a significant part of their analytic formalism in favour of a detailed physics applied to a complete envelope model, in which the stellar structure equations are integrated from the atmosphere down to the bottom of the hydrogen-burning shell. This allows us to predict self-consistently: (i) the effective temperature, and more generally the convective envelope and atmosphere structures, correctly coupled to the changes in the surface chemical abundances and gas opacities; (ii) the conditions under which sphericity effects may significantly affect the atmospheres of giant stars; (iii) the core mass-luminosity relation and its possible break-down due to the occurrence of hot-bottom burning (HBB) in the most massive AGB stars, by taking properly into account the nuclear energy generation in the H-burning shell and in the deepest layers of the convective envelope; (iv) the HBB nucleosynthesis via the solution of a complete nuclear network (including the pp chains, and the CNO, NeNa and MgAl cycles) coupled to a diffusive description of mixing, suitable to follow also the synthesis of 7Li via the Cameron-Fowler beryllium transport mechanism; (v) the intershell abundances left by each thermal pulse via the solution of a complete nuclear network applied to a simple model of the pulse-driven convective zone (PDCZ); (vi) the onset and quenching of the third dredge-up, with a temperature criterion that is applied, at each thermal pulse, to the result of envelope integrations at the stage of the post-flash luminosity peak. At the same time, COLIBRI pioneers new techniques in the treatment of the physics of stellar interiors, not yet adopted in full TP-AGB models. It is the first evolutionary code ever to use accurate on-the-fly computation of the equation of state (EoS) for roughly 800

  19. The stellar spectral features of nearby galaxies in the near infrared: tracers of thermally pulsing asymptotic giant branch stars?

    NASA Astrophysics Data System (ADS)

    Riffel, Rogério; Mason, Rachel E.; Martins, Lucimara P.; Rodríguez-Ardila, Alberto; Ho, Luis C.; Riffel, Rogemar A.; Lira, Paulina; Gonzalez Martin, Omaira; Ruschel-Dutra, Daniel; Alonso-Herrero, Almudena; Flohic, Helene; McDermid, Richard M.; Ramos Almeida, Cristina; Thanjavur, Karun; Winge, Claudia

    2015-07-01

    We analyse the stellar absorption features in high signal-to-noise ratio (S/N) near-infrared (NIR) spectra of the nuclear region of 12 nearby galaxies, mostly spirals. The features detected in some or all of the galaxies in this sample are the TiO (0.843 and 0.886 μm), VO (1.048 μm), CN (1.1 and 1.4 μm), H2O (1.4 and 1.9 μm) and CO (1.6 and 2.3 μm) bands. The C2 (1.17 and 1.76 μm) bands are generally weak or absent, although C2 (1.76 μm) may be weakly present in the mean galaxy spectrum. A deep feature near 0.93 μm, likely caused by CN, TiO and/or ZrO, is also detected in all objects. Fitting a combination of stellar spectra to the mean spectrum shows that the absorption features are produced by evolved stars: cool giants and supergiant stars in the early- or thermally pulsing asymptotic giant branch (E-AGB or TP-AGB) phases. The high luminosity of TP-AGB stars, and the appearance of VO and ZrO features in the data, suggest that TP-AGB stars dominate these spectral features. However, a contribution from other evolved stars is also likely. Comparison with evolutionary population synthesis models shows that models based on empirical libraries that predict relatively strong NIR features provide a more accurate description of the data. However, none of the models tested accurately reproduces all of the features observed in the spectra. To do so, the models will need to not only improve the treatment of TP-AGB stars, but also include good quality spectra of red giant and E-AGB stars. The uninterrupted wavelength coverage, high S/N and quantity of features we present here will provide a benchmark for the next generation of models aiming to explain and predict the NIR properties of galaxies.

  20. THE DUST BUDGET OF THE SMALL MAGELLANIC CLOUD: ARE ASYMPTOTIC GIANT BRANCH STARS THE PRIMARY DUST SOURCE AT LOW METALLICITY?

    SciTech Connect

    Boyer, M. L.; Gordon, K. D.; Meixner, M.; Sargent, B. A.; Srinivasan, S.; Riebel, D.; McDonald, I.; Van Loon, J. Th.; Clayton, G. C.; Sloan, G. C.

    2012-03-20

    We estimate the total dust input from the cool evolved stars in the Small Magellanic Cloud, using the 8 {mu}m excess emission as a proxy for the dust-production rate (DPR). We find that asymptotic giant branch (AGB) and red supergiant (RSG) stars produce (8.6-9.5) Multiplication-Sign 10{sup -7} M{sub Sun} yr{sup -1} of dust, depending on the fraction of far-infrared sources that belong to the evolved star population (with 10%-50% uncertainty in individual DPRs). RSGs contribute the least (<4%), while carbon-rich AGB stars (especially the so-called extreme AGB stars) account for 87%-89% of the total dust input from cool evolved stars. We also estimate the dust input from hot stars and supernovae (SNe), and find that if SNe produce 10{sup -3} M{sub Sun} of dust each, then the total SN dust input and AGB input are roughly equivalent. We consider several scenarios of SN dust production and destruction and find that the interstellar medium (ISM) dust can be accounted for solely by stellar sources if all SNe produce dust in the quantities seen around the dustiest examples and if most SNe explode in dense regions where much of the ISM dust is shielded from the shocks. We find that AGB stars contribute only 2.1% of the ISM dust. Without a net positive contribution from SNe to the dust budget, this suggests that dust must grow in the ISM or be formed by another unknown mechanism.

  1. Connecting the evolution of thermally pulsing asymptotic giant branch stars to the chemistry in their circumstellar envelopes - I. Hydrogen cyanide

    NASA Astrophysics Data System (ADS)

    Marigo, Paola; Ripamonti, Emanuele; Nanni, Ambra; Bressan, Alessandro; Girardi, Léo

    2016-02-01

    We investigate the formation of hydrogen cyanide (HCN) in the inner circumstellar envelopes of thermally pulsing asymptotic giant branch (TP-AGB) stars. A dynamic model for periodically shocked atmospheres, which includes an extended chemo-kinetic network, is for the first time coupled to detailed evolutionary tracks for the TP-AGB phase computed with the COLIBRI code. We carried out a calibration of the main shock parameters (the shock formation radius rs,0 and the effective adiabatic index γ _ad^eff) using the circumstellar HCN abundances recently measured for a populous sample of pulsating TP-AGB stars. Our models recover the range of the observed HCN concentrations as a function of the mass-loss rates, and successfully reproduce the systematic increase of HCN moving along the M-S-C chemical sequence of TP-AGB stars, which traces the increase of the surface C/O ratio. The chemical calibration brings along two important implications for the physical properties of the pulsation-induced shocks: (i) the first shock should emerge very close to the photosphere (rs,0 ≃ 1R), and (ii) shocks are expected to have a dominant isothermal character (γ _ad^eff˜eq 1) in the denser region close to the star (within ˜3-4R), implying that radiative processes should be quite efficient. Our analysis also suggests that the HCN concentrations in the inner circumstellar envelopes are critically affected by the H-H2 chemistry during the post-shock relaxation stages. Given the notable sensitiveness of the results to stellar parameters, this paper shows that such chemo-dynamic analyses may indeed provide a significant contribution to the broader goal of attaining a comprehensive calibration of the TP-AGB evolutionary phase.

  2. PROBING SUBSTELLAR COMPANIONS OF ASYMPTOTIC GIANT BRANCH STARS THROUGH SPIRALS AND ARCS

    SciTech Connect

    Kim, Hyosun; Taam, Ronald E. E-mail: taam@tonic.astro.northwestern.edu

    2012-01-10

    Recent observations of strikingly well-defined spirals in the circumstellar envelopes of asymptotic giant branch (AGB) stars point to the existence of binary companions in these objects. In the case of planet- or brown-dwarf-mass companions, we investigate the observational properties of the spiral-onion shell wakes due to the gravitational interaction of these companions with the outflowing circumstellar matter. Three-dimensional hydrodynamical simulations at high resolution show that the substellar mass objects produce detectable signatures, corresponding to density contrasts (10%-200%) and arm separations (10-400 AU) at 100 AU distance from the central star, for the wake induced by a Jupiter to brown-dwarf-mass object orbiting a solar mass AGB star. In particular, the arm pattern propagates in the radial direction with a speed depending on the local wind speed and sound speed, implying possible variations of the arm separation in the wind acceleration region and/or in a slow wind with significant temperature variation. The pattern propagation speeds of the inner and outer boundaries differ by twice the sound speed, leading to the overlap of high-density boundaries in slow winds and producing a subpattern of the spiral arm feature. Vertically, the wake forms concentric arcs with angular sizes anticorrelated to the wind Mach number. We provide an empirical formula for the peak density enhancement as a function of the mass, orbital distance, and velocity of the object as well as the wind and local sound speed. In typical conditions of AGB envelopes, the arm-interarm density contrast can be greater than 30% of the background density within a distance of {approx}10 (M{sub p} /M{sub J} ) AU for the object mass M{sub p} in units of Jupiter mass M{sub J} . These results suggest that such features may probe unseen substellar mass objects embedded in the winds of AGB stars and may be useful in planning future high-sensitivity/resolution observations with the Atacama Large

  3. Dynamos in asymptotic-giant-branch stars as the origin of magnetic fields shaping planetary nebulae.

    PubMed

    Blackman, E G; Frank, A; Markiel, J A; Thomas, J H; Van Horn, H M

    2001-01-25

    Planetary nebulae are thought to be formed when a slow wind from the progenitor giant star is overtaken by a subsequent fast wind generated as the star enters its white dwarf stage. A shock forms near the boundary between the winds, creating the relatively dense shell characteristic of a planetary nebula. A spherically symmetric wind will produce a spherically symmetric shell, yet over half of known planetary nebulae are not spherical; rather, they are elliptical or bipolar in shape. A magnetic field could launch and collimate a bipolar outflow, but the origin of such a field has hitherto been unclear, and some previous work has even suggested that a field could not be generated. Here we show that an asymptotic-giant-branch (AGB) star can indeed generate a strong magnetic field, having as its origin a dynamo at the interface between the rapidly rotating core and the more slowly rotating envelope of the star. The fields are strong enough to shape the bipolar outflows that produce the observed bipolar planetary nebulae. Magnetic braking of the stellar core during this process may also explain the puzzlingly slow rotation of most white dwarf stars. PMID:11206538

  4. Barium isotopic composition of mainstream silicon carbides from Murchison: Constraints for s-process nucleosynthesis in asymptotic giant branch stars

    SciTech Connect

    Liu, Nan; Davis, Andrew M.; Pellin, Michael J.; Dauphas, Nicolas; Savina, Michael R.; Gallino, Roberto; Bisterzo, Sara; Straniero, Oscar; Cristallo, Sergio; Gyngard, Frank; Willingham, David G.; Pignatari, Marco; Herwig, Falk

    2014-05-01

    We present barium, carbon, and silicon isotopic compositions of 38 acid-cleaned presolar SiC grains from Murchison. Comparison with previous data shows that acid washing is highly effective in removing barium contamination. Strong depletions in δ({sup 138}Ba/{sup 136}Ba) values are found, down to –400‰, which can only be modeled with a flatter {sup 13}C profile within the {sup 13}C pocket than is normally used. The dependence of δ({sup 138}Ba/{sup 136}Ba) predictions on the distribution of {sup 13}C within the pocket in asymptotic giant branch (AGB) models allows us to probe the {sup 13}C profile within the {sup 13}C pocket and the pocket mass in AGB stars. In addition, we provide constraints on the {sup 22}Ne(α, n){sup 25}Mg rate in the stellar temperature regime relevant to AGB stars, based on δ({sup 134}Ba/{sup 136}Ba) values of mainstream grains. We found two nominally mainstream grains with strongly negative δ({sup 134}Ba/{sup 136}Ba) values that cannot be explained by any of the current AGB model calculations. Instead, such negative values are consistent with the intermediate neutron capture process (i process), which is activated by the very late thermal pulse during the post-AGB phase and characterized by a neutron density much higher than the s process. These two grains may have condensed around post-AGB stars. Finally, we report abundances of two p-process isotopes, {sup 130}Ba and {sup 132}Ba, in single SiC grains. These isotopes are destroyed in the s process in AGB stars. By comparing their abundances with respect to that of {sup 135}Ba, we conclude that there is no measurable decay of {sup 135}Cs (t {sub 1/2} = 2.3 Ma) to {sup 135}Ba in individual SiC grains, indicating condensation of barium, but not cesium into SiC grains before {sup 135}Cs decayed.

  5. Evolution and nucleosynthesis of helium-rich asymptotic giant branch models

    NASA Astrophysics Data System (ADS)

    Shingles, Luke J.; Doherty, Carolyn L.; Karakas, Amanda I.; Stancliffe, Richard J.; Lattanzio, John C.; Lugaro, Maria

    2015-09-01

    There is now strong evidence that some stars have been born with He mass fractions as high as Y ≈ 0.40 (e.g. in ω Centauri). However, the advanced evolution, chemical yields, and final fates of He-rich stars are largely unexplored. We investigate the consequences of He-enhancement on the evolution and nucleosynthesis of intermediate-mass asymptotic giant branch (AGB) models of 3, 4, 5, and 6 M⊙ with a metallicity of Z = 0.0006 ([Fe/H] ≈ -1.4). We compare models with He-enhanced compositions (Y = 0.30, 0.35, 0.40) to those with primordial-He (Y = 0.24). We find that the minimum initial mass for C burning and super-AGB stars with CO(Ne) or ONe cores decreases from above our highest mass of 6 to ˜4-5 M⊙ with Y = 0.40. We also model the production of trans-Fe elements via the slow neutron-capture process (s-process). He-enhancement substantially reduces the third dredge-up efficiency and the stellar yields of s-process elements (e.g. 90 per cent less Ba for 6 M⊙, Y = 0.40). An exception occurs for 3 M⊙, where the near-doubling in the number of thermal pulses with Y = 0.40 leads to ˜50 per cent higher yields of Ba-peak elements and Pb if the 13C neutron source is included. However, the thinner intershell and increased temperatures at the base of the convective envelope with Y = 0.40 probably inhibit the 13C neutron source at this mass. Future chemical evolution models with our yields might explain the evolution of s-process elements among He-rich stars in ω Centauri.

  6. Heavy elements in globular clusters: The role of asymptotic giant branch stars

    SciTech Connect

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

    2014-04-10

    Recent observations of heavy elements in globular clusters reveal intriguing deviations from the standard paradigm of the early galactic nucleosynthesis. If the r-process contamination is a common feature of halo stars, s-process enhancements are found in a few globular clusters only. We show that the combined pollution of asymptotic giant branch (AGB) stars with a mass ranging between 3 to 6 M {sub ☉} may account for most of the features of the s-process overabundance in M4 and M22. In these stars, the s process is a mixture of two very different neutron-capture nucleosynthesis episodes. The first is due to the {sup 13}C(α, n){sup 16}O reaction and takes place during the interpulse periods. The second is due to the {sup 22}Ne(α, n){sup 25}Mg reaction and takes place in the convective zones generated by thermal pulses. The production of the heaviest s elements (from Ba to Pb) requires the first neutron burst, while the second produces large overabundances of light s (Rb, Sr, Y, Zr). The first mainly operates in the less massive AGB stars, while the second dominates in the more massive. From the heavy-s/light-s ratio, we derive that the pollution phase should last for 150 ± 50 Myr, a period short enough compared to the formation timescale of the globular cluster system, but long enough to explain why the s-process pollution is observed in a few cases only. With few exceptions, our theoretical prediction provides a reasonable reproduction of the observed s-process abundances, from Sr to Hf. However, Ce is probably underproduced by our models, while Rb and Pb are overproduced. Possible solutions are discussed.

  7. FORETELLINGS OF RAGNAROeK: WORLD-ENGULFING ASYMPTOTIC GIANTS AND THE INHERITANCE OF WHITE DWARFS

    SciTech Connect

    Mustill, Alexander J.; Villaver, Eva

    2012-12-20

    The search for planets around white dwarf stars, and evidence for dynamical instability around them in the form of atmospheric pollution and circumstellar disks, raises questions about the nature of planetary systems that can survive the vicissitudes of the asymptotic giant branch (AGB). We study the competing effects, on planets at several AU from the star, of strong tidal forces arising from the star's large convective envelope, and of the planets' orbital expansion due to stellar mass loss. We study, for the first time, the evolution of planets while following each thermal pulse on the AGB. For Jovian planets, tidal forces are strong, and can pull into the envelope planets initially at {approx}3 AU for a 1 M{sub Sun} star and {approx}5 AU for a 5 M{sub Sun} star. Lower-mass planets feel weaker tidal forces, and terrestrial planets initially within 1.5-3 AU enter the stellar envelope. Thus, low-mass planets that begin inside the maximum stellar radius can survive, as their orbits expand due to mass loss. The inclusion of a moderate planetary eccentricity slightly strengthens the tidal forces experienced by Jovian planets. Eccentric terrestrial planets are more at risk, since their eccentricity does not decay and their small pericenter takes them inside the stellar envelope. We also find the closest radii at which planets will be found around white dwarfs, assuming that any planet entering the stellar envelope is destroyed. Planets are in that case unlikely to be found inside {approx}1.5 AU of a white dwarf with a 1 M{sub Sun} progenitor and {approx}10 AU of a white dwarf with a 5 M{sub Sun} progenitor.

  8. Sulfur in presolar silicon carbide grains from asymptotic giant branch stars

    NASA Astrophysics Data System (ADS)

    Hoppe, Peter; Lodders, Katharina; Fujiya, Wataru

    2015-06-01

    We studied 14 presolar SiC mainstream grains for C-, Si-, and S-isotopic compositions and S elemental abundances. Ten grains have low levels of S contamination and CI chondrite-normalized S/Si ratios between 2 × 10-5 and 2 × 10-4. All grains have S-isotopic compositions compatible within 2σ of solar values. Their mean S isotope composition deviates from solar by at most a few percent, and is consistent with values observed for the carbon star IRC+10216, believed to be a representative source star of the grains, and the interstellar medium. The isotopic data are also consistent with stellar model predictions of low-mass asymptotic giant branch (AGB) stars. In a δ33S versus δ34S plot the data fit along a line with a slope of 1.8 ± 0.7, suggesting imprints from galactic chemical evolution. The observed S abundances are lower than expected from equilibrium condensation of CaS in solid solution with SiC under pressure and temperature conditions inferred from the abundances of more refractory elements in SiC. Calcium to S abundance ratios are generally above unity, contrary to expectations for stoichiometric CaS solution in the grains, possibly due to condensation of CaC2 into SiC. We observed a correlation between Mg and S abundances suggesting solid solution of MgS in SiC. The low abundances of S in mainstream grains support the view that the significantly higher abundances of excess 32S found in some Type AB SiC grains are the result of in situ decay of radioactive 32Si from born-again AGB stars that condensed into AB grains.

  9. Asymptotic giant branch stars in the Large Magellanic Cloud: evolution of dust in circumstellar envelopes

    NASA Astrophysics Data System (ADS)

    Dell'Agli, F.; Ventura, P.; Schneider, R.; Di Criscienzo, M.; García-Hernández, D. A.; Rossi, C.; Brocato, E.

    2015-03-01

    We calculated theoretical evolutionary sequences of asymptotic giant branch (AGB) stars, including the formation and evolution of dust grains in their circumstellar envelopes. By considering stellar populations of the Large Magellanic Cloud (LMC), we calculate synthetic colour-colour and colour-magnitude diagrams, which are compared with those obtained by the Spitzer Space Telescope. The comparison between observations and theoretical predictions outlines that extremely obscured carbon stars and oxygen-rich sources experiencing hot bottom burning (HBB) occupy well-defined, distinct regions in the colour-colour ([3.6] - [4.5], [5.8] - [8.0]) diagram. The C-rich stars are distributed along a diagonal strip that we interpret as an evolutionary sequence, becoming progressively more obscured as the stellar surface layers enrich in carbon. Their circumstellar envelopes host solid carbon dust grains with size in the range 0.05 < a < 0.2 μm. The presence of silicon carbide (SiC) particles is expected only in the more metal-rich stars. The reddest sources, with [3.6] - [4.5] > 2, are the descendants of stars with initial mass Min ˜ 2.5-3 M⊙ in the very latest phases of AGB life. The oxygen-rich stars with the reddest colours ([5.8] - [8.0] > 0.6) are those experiencing HBB, the descendants of ˜5 M⊙ objects formed 108 yr ago; alumina and silicate dust starts forming at different distances from the central star. The overall dust production rate in the LMC is ˜4.5 × 10-5 M⊙ yr-1, the relative percentages due to C and M stars being 85 and 15 per cent, respectively.

  10. Magnetohydrodynamics and deep mixing in evolved stars. I. Two- and three-dimensional analytical models for the asymptotic giant branch

    SciTech Connect

    Nucci, M. C.; Busso, M. E-mail: busso@fisica.unipg.it

    2014-06-01

    The advection of thermonuclear ashes by magnetized domains emerging near the H shell was suggested to explain asymptotic giant branch (AGB) star abundances. Here we verify this idea quantitatively through exact MHD models. Starting with a simple two-dimensional (2D) geometry and in an inertia frame, we study plasma equilibria avoiding the complications of numerical simulations. We show that below the convective envelope of an AGB star, variable magnetic fields induce a natural expansion, permitted by the almost ideal MHD conditions, in which the radial velocity grows as the second power of the radius. We then study the convective envelope, where the complexity of macroturbulence allows only for a schematic analytical treatment. Here the radial velocity depends on the square root of the radius. We then verify the robustness of our results with 3D calculations for the velocity, showing that for both studied regions the solution previously found can be seen as a planar section of a more complex behavior, in which the average radial velocity retains the same dependency on the radius found in 2D. As a final check, we compare our results to approximate descriptions of buoyant magnetic structures. For realistic boundary conditions, the envelope crossing times are sufficient to disperse in the huge convective zone any material transported, suggesting magnetic advection as a promising mechanism for deep mixing. The mixing velocities are smaller than for convection but larger than for diffusion and adequate for extra mixing in red giants.

  11. Dust Production from Sub-Solar to Super-Solar Metallicity in Thermally Pulsing Asymptotic Giant Branch Stars

    NASA Astrophysics Data System (ADS)

    Nanni, A.; Bressan, A.; Marigo, P.; Girardi, L.; Javadi, A.; van Loon, J. Th.

    2015-08-01

    We discuss the dust chemistry and growth in the circumstellar envelopes (CSEs) of Thermally Pulsing Asymptotic Giant Branch (TP-AGB) star models, computed with the COLIBRI code, at varying initial mass and metallicity (Z = 0.001, 0.008, 0.02, 0.04, 0.06). A relevant result of our analysis deals with silicate production in M stars. We show that, in order to reproduce the observed trend between terminal velocities and mass-loss rates in Galactic M giants, one has to significantly reduce the efficiency of chemisputtering by H2 molecules, usually considered the most effective dust destruction mechanism. This conclusion is in agreement with the most recent laboratory results, which show that silicates may condense already at Tcond˜1400 K, rather than only at Tcond˜1000 K, as obtained by models that include chemisputtering. From analysis of the total dust ejecta, we find that the dust-to-gas ratios of the total ejecta from intermediate-mass stars are much less dependent on metallicity than usually assumed. In a broader context, our results are suitable for studying the dust enrichment of the interstellar medium provided by TP-AGB stars in both nearby and high-redshift galaxies.

  12. Nucleosynthesis in helium-enriched asymptotic giant branch models: Implications for heavy element enrichment in ω Centauri

    SciTech Connect

    Karakas, Amanda I.; Marino, Anna F.; Nataf, David M.

    2014-03-20

    We investigate the effect of helium enrichment on the evolution and nucleosynthesis of low-mass asymptotic giant branch (AGB) stars of 1.7 M {sub ☉} and 2.36 M {sub ☉} with a metallicity of Z = 0.0006 ([Fe/H] ≈–1.4). We calculate evolutionary sequences with the primordial helium abundance (Y = 0.24) and with helium-enriched compositions (Y = 0.30, 0.35, 0.40). For comparison, we calculate models of the same mass but at a lower metallicity Z = 0.0003 ([Fe/H] ≈–1.8) with Y = 0.24. Post-processing nucleosynthesis calculations are performed on each of the evolutionary sequences to determine the production of elements from hydrogen to bismuth. Elemental surface abundance predictions and stellar yields are presented for each model. The models with enriched helium have shorter main sequence and AGB lifetimes, and they enter the AGB with a more massive hydrogen-exhausted core than the primordial helium model. The main consequences are as follows: (1) low-mass AGB models with enhanced helium will evolve more than twice as fast, giving them the chance to contribute sooner to the chemical evolution of the forming globular clusters, and (2) the stellar yields will be strongly reduced relative to their primordial helium counterparts. An increase of ΔY = 0.10 at a given mass decreases the yields of carbon by up to ≈60% and of fluorine by up to 80%; it also decreases the yields of the s-process elements barium and lanthanum by ≈45%. While the yields of first s-process peak elements strontium, yttrium, and zirconium decrease by up to 50%, the yields of rubidium either do not change or increase.

  13. THE ASYMPTOTIC GIANT BRANCH AND THE TIP OF THE RED GIANT BRANCH AS PROBES OF STAR FORMATION HISTORY: THE NEARBY DWARF IRREGULAR GALAXY KKH 98

    SciTech Connect

    Melbourne, J.; Williams, B.; Dalcanton, J.; Ammons, S. M.; Max, C.; Koo, D. C.; Dolphin, A. E-mail: ben@astro.washington.ed E-mail: ammons@ucolick.or E-mail: koo@ucolick.or E-mail: adolphin@raytheon.co

    2010-03-20

    We investigate the utility of the asymptotic giant branch (AGB) and the red giant branch (RGB) as probes of the star formation history (SFH) of the nearby (D = 2.5 Mpc) dwarf irregular galaxy, KKH 98. Near-infrared (near-IR) Keck Laser Guide Star Adaptive Optics (AO) images resolve 592 IR-bright stars reaching over 1 mag below the tip of the RGB. Significantly deeper optical (F475W and F814W) Hubble Space Telescope images of the same field contain over 2500 stars, reaching to the red clump and the main-sequence turnoff for 0.5 Gyr old populations. Compared to the optical color-magnitude diagram (CMD), the near-IR CMD shows significantly tighter AGB sequences, providing a good probe of the intermediate-age (0.5-5 Gyr) populations. We match observed CMDs with stellar evolution models to recover the SFH of KKH 98. On average, the galaxy has experienced relatively constant low-level star formation (5 x 10{sup -4} M{sub sun} yr{sup -1}) for much of cosmic time. Except for the youngest main-sequence populations (age <0.1 Gyr), which are typically fainter than the AO data flux limit, the SFH estimated from the 592 IR-bright stars is a reasonable match to that derived from the much larger optical data set. Differences between the optical- and IR-derived SFHs for 0.1-1 Gyr populations suggest that current stellar evolution models may be overproducing the AGB by as much as a factor of 3 in this galaxy. At the depth of the AO data, the IR-luminous stars are not crowded. Therefore, these techniques can potentially be used to determine the stellar populations of galaxies at significantly further distances.

  14. 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

  15. AKARI All Sky Survey: contribution from AGB stars to the far infrared flux from the Milky Way related to point sources outside the Galactic plane

    NASA Astrophysics Data System (ADS)

    Pollo, A.; Takeuchi, T. T.; Rybka, P.

    2011-10-01

    Using data from the FIS AKARI All-Sky Survey, we make a first step towards the estimation of the contribution from Asymptotic Giant Branch (AGB) stars to the far-infrared (FIR) flux from the Milky Way. We estimate the contribution from the AGB, and post-AGB, stars to the total flux generated by point sources outside the Galactic plane. Additionally, we present the positions of different types of AGB, and post-AGB, stars in the FIR color-color diagrams. Our main conclusion is that there is a high contribution from AGB stars, and particularly post-AGB stars, to the FIR flux coming from point sources in the outer parts of the Milky Way and possibly other Milky Way-type galaxies. FIR colors of different types of AGB stars remain similar but post-AGB stars are redder in the FIR and, as a result, contribute more to the total Galaxy flux density at longer FIR wavelengths.

  16. Inverse Kinematic Study of the Alg26(d ,p )27Al Reaction and Implications for Destruction of 26Al in Wolf-Rayet and Asymptotic Giant Branch Stars

    NASA Astrophysics Data System (ADS)

    Margerin, V.; Lotay, G.; Woods, P. J.; Aliotta, M.; Christian, G.; Davids, B.; Davinson, T.; Doherty, D. T.; Fallis, J.; Howell, D.; Kirsebom, O. S.; Mountford, D. J.; Rojas, A.; Ruiz, C.; Tostevin, J. A.

    2015-08-01

    In Wolf-Rayet and asymptotic giant branch (AGB) stars, the Alg26(p ,γ )27Si reaction is expected to govern the destruction of the cosmic γ -ray emitting nucleus 26Al. The rate of this reaction, however, is highly uncertain due to the unknown properties of key resonances in the temperature regime of hydrogen burning. We present a high-resolution inverse kinematic study of the Alg26(d ,p )27Al reaction as a method for constraining the strengths of key astrophysical resonances in the Alg26(p ,γ )27Si reaction. In particular, the results indicate that the resonance at Er=127 keV in 27Si determines the entire Alg26(p ,γ )27Si reaction rate over almost the complete temperature range of Wolf-Rayet stars and AGB stars.

  17. 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.

  18. Evolution of long-lived globular cluster stars. II. Sodium abundance variations on the asymptotic giant branch as a function of globular cluster age and metallicity

    NASA Astrophysics Data System (ADS)

    Charbonnel, Corinne; Chantereau, William

    2016-02-01

    Context. Long-lived stars in globular clusters exhibit chemical peculiarities with respect to their halo counterparts. In particular, sodium-enriched stars are identified as belonging to a second stellar population born from cluster material contaminated by the hydrogen-burning ashes of a first stellar population. Their presence and numbers in different locations of the colour-magnitude diagram provide important constraints on the self-enrichment scenarios. In particular, the ratio of Na-poor to Na-rich stars on the asymptotic giant branch (AGB) has recently been found to vary strongly from cluster to cluster (NGC 6752, 47 Tuc, and NGC 2808), while it is relatively constant on the red giant branch (RGB). Aims: We investigate the impact of both age and metallicity on the theoretical sodium spread along the AGB within the framework of the fast rotating massive star (FRMS) scenario for globular cluster self-enrichment. Methods: We computed evolution models of low-mass stars for four different metallicities ([Fe/H] = -2.2, -1.75, -1.15, -0.5) assuming the initial helium-sodium abundance correlation for second population stars derived from the FRMS models and using mass loss prescriptions on the RGB with two realistic values of the free parameter in the Reimers formula. Results: Based on this grid of models we derive the theoretical critical initial mass for a star born with a given helium, sodium, and metal content that determines whether that star will climb or not the AGB. This allows us to predict the maximum sodium content expected on the AGB for globular clusters as a function of both their metallicity and age. We find that (1) at a given metallicity, younger clusters are expected to host AGB stars exhibiting a larger sodium spread than older clusters and (2) at a given age, higher sodium dispersion along the AGB is predicted in the most metal-poor globular clusters than in the metal-rich ones. We also confirm the strong impact of the mass loss rate in the earlier

  19. K{sub s} -BAND LUMINOSITY EVOLUTION OF THE ASYMPTOTIC GIANT BRANCH POPULATION BASED ON STAR CLUSTERS IN THE LARGE MAGELLANIC CLOUD

    SciTech Connect

    Ko, Youkyung; Lee, Myung Gyoon; Lim, Sungsoon E-mail: mglee@astro.snu.ac.kr

    2013-11-10

    We present a study of K{sub s} -band luminosity evolution of the asymptotic giant branch (AGB) population in simple stellar systems using star clusters in the Large Magellanic Cloud (LMC). We determine physical parameters of LMC star clusters including center coordinates, radii, and foreground reddenings. Ages of 83 star clusters are derived from isochrone fitting with the Padova models, and those of 19 star clusters are taken from the literature. The AGB stars in 102 star clusters with log(age) = 7.3-9.5 are selected using near-infrared color-magnitude diagrams based on Two Micron All Sky Survey photometry. Then we obtain the K{sub s} -band luminosity fraction of AGB stars in these star clusters as a function of ages. The K{sub s} -band luminosity fraction of AGB stars increases, on average, as age increases from log(age) ∼ 8.0, reaching a maximum at log(age) ∼ 8.5, and it decreases thereafter. There is a large scatter in the AGB luminosity fraction for given ages, which is mainly due to stochastic effects. We discuss this result in comparison with five simple stellar population models. The maximum K{sub s} -band AGB luminosity fraction for bright clusters is reproduced by the models that expect the value of 0.7-0.8 at log(age) = 8.5-8.7. We discuss the implication of our results with regard to the study of size and mass evolution of galaxies.

  20. First Detection of Ultraviolet Emission from a Detached Dust Shell: Galaxy Evolution Explorer Observations of the Carbon Asymptotic Giant Branch Star U Hya

    NASA Astrophysics Data System (ADS)

    Sanchez, Enmanuel; Montez, Rodolfo, Jr.; Ramstedt, Sofia; Stassun, Keivan G.

    2015-01-01

    We present the discovery of an extended ring of ultraviolet (UV) emission surrounding the asymptotic giant branch (AGB) star U Hya in archival observations performed by the Galaxy Evolution Explorer. This is the third discovery of extended UV emission from a carbon AGB star and the first from an AGB star with a detached shell. From imaging and photometric analysis of the FUV and NUV images, we determined that the UV ring has a radius of ~110'', thus indicating that the emitting material is likely associated with the detached shell seen in the infrared. We find that scattering of the central point source of NUV and FUV emission by the dust shell is negligible. Moreover, we find that scattering of the interstellar radiation field by the dust shell can contribute at most ~10% of the FUV flux. Morphological and photometric evidence suggests that shocks caused by the star's motion through space and, possibly, shock-excited H2 molecules are the most likely origins of the UV flux. In contrast to previous examples of extended UV emission from AGB stars, the extended UV emission from U Hya does not show a bow-shock-like structure, which is consistent with a lower space velocity and lower interstellar medium density. This suggests the detached dust shell is the source of the UV-emitting material and can be used to better understand the formation of detached shells.

  1. FIRST DETECTION OF ULTRAVIOLET EMISSION FROM A DETACHED DUST SHELL: GALAXY EVOLUTION EXPLORER OBSERVATIONS OF THE CARBON ASYMPTOTIC GIANT BRANCH STAR U Hya

    SciTech Connect

    Sanchez, Enmanuel; Montez, Rodolfo Jr.; Stassun, Keivan G.; Ramstedt, Sofia

    2015-01-10

    We present the discovery of an extended ring of ultraviolet (UV) emission surrounding the asymptotic giant branch (AGB) star U Hya in archival observations performed by the Galaxy Evolution Explorer. This is the third discovery of extended UV emission from a carbon AGB star and the first from an AGB star with a detached shell. From imaging and photometric analysis of the FUV and NUV images, we determined that the UV ring has a radius of ∼110'', thus indicating that the emitting material is likely associated with the detached shell seen in the infrared. We find that scattering of the central point source of NUV and FUV emission by the dust shell is negligible. Moreover, we find that scattering of the interstellar radiation field by the dust shell can contribute at most ∼10% of the FUV flux. Morphological and photometric evidence suggests that shocks caused by the star's motion through space and, possibly, shock-excited H{sub 2} molecules are the most likely origins of the UV flux. In contrast to previous examples of extended UV emission from AGB stars, the extended UV emission from U Hya does not show a bow-shock-like structure, which is consistent with a lower space velocity and lower interstellar medium density. This suggests the detached dust shell is the source of the UV-emitting material and can be used to better understand the formation of detached shells.

  2. 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.

  3. Puzzling Origin of CEMP-r/s Stars: An Interpretation of Abundance and Enrichment of s- and r-Process Elements from Asymptotic Giant Branch Supernovae

    NASA Astrophysics Data System (ADS)

    Zhang, Jiang; Zhao, Fang; Chen, Yanping; Cui, Wenyuan; Zhang, Bo

    2013-12-01

    CEMP-r/s stars at low metallicity are known as double-enhanced stars that show enhancements of both r-process and s-process elements. The chemical abundances of these very metal-poor stars provide us a lot of information for putting new restraints on models of neutron-capture processes. In this article, we put forward an accreted scenario in which the double enrichment of r-process and s-process elements is caused by a former intermediate-mass Asymptotic Giant Branch (AGB) companion in a detached binary system. As the AGB superwind is only present at the ultimate phase of AGB stars, there is thus a lot of potential that the degenerate-core mass of an intermediate-mass AGB star reaches the Chandrasekhar limit before the AGB superwind. In these circumstances, both s-process elements produced in the AGB shell and r-process elements synthesized in the subsequent explosion would be sprayed contemporaneously and accreted by its companion. Despite similarity to physical conditions of a core-collapse supernova, a major focus in this scenario is the degenerate C-O core surrounded by an envelope of a former intermediate-mass AGB donor that may collapse and explode. Due to the existence of an outer envelope, r-process nucleosynthesis is expected to occur. Hypothesizing the material-rich europium (Eu) accreted by the secondary via the wind from the supernova to be in proportion to the geometric fraction of the companion with respect to the exploding donor star, we find that the estimated yield of Eu (as representative of r-process elements) per AGB supernova event is about 1 × 10-9 M ⊙ ˜ 5 × 10-9 M ⊙. Using the yields of Eu, the overabundance of r-process elements in CEMP-r/s stars can be accounted for. The calculated results show that the value of parameter f , standing for efficiency of wind pollution from the AGB supernova, will reach about 104, which means that the enhanced factor is much larger than unity due to the impact of gravity of the donor and the result of

  4. EVOLUTION, NUCLEOSYNTHESIS, AND YIELDS OF LOW-MASS ASYMPTOTIC GIANT BRANCH STARS AT DIFFERENT METALLICITIES. II. THE FRUITY DATABASE

    SciTech Connect

    Cristallo, S.; Dominguez, I.; Abia, C.; Piersanti, L.; Straniero, O.; Gallino, R.; Di Rico, G.; Quintini, M.; Bisterzo, S.

    2011-12-01

    By using updated stellar low-mass stars models, we systematically investigate the nucleosynthesis processes occurring in asymptotic giant branch (AGB) stars. In this paper, we present a database dedicated to the nucleosynthesis of AGB stars: FRANEC Repository of Updated Isotopic Tables and Yields (FRUITY). An interactive Web-based interface allows users to freely download the full (from H to Bi) isotopic composition, as it changes after each third dredge-up (TDU) episode and the stellar yields the models produce. A first set of AGB models, having masses in the range 1.5 {<=}M/M{sub Sun} {<=} 3.0 and metallicities 1 Multiplication-Sign 10{sup -3} {<=} Z {<=} 2 Multiplication-Sign 10{sup -2}, is discussed. For each model, a detailed description of the physical and the chemical evolution is provided. In particular, we illustrate the details of the s-process and we evaluate the theoretical uncertainties due to the parameterization adopted to model convection and mass loss. The resulting nucleosynthesis scenario is checked by comparing the theoretical [hs/ls] and [Pb/hs] ratios to those obtained from the available abundance analysis of s-enhanced stars. On the average, the variation with the metallicity of these spectroscopic indexes is well reproduced by theoretical models, although the predicted spread at a given metallicity is substantially smaller than the observed one. Possible explanations for such a difference are briefly discussed. An independent check of the TDU efficiency is provided by the C-stars luminosity function. Consequently, theoretical C-stars luminosity functions for the Galactic disk and the Magellanic Clouds have been derived. We generally find good agreement with observations.

  5. 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

  6. Asymptotic Giant Branch stars as a source of short-lived radioactive nuclei in the solar nebula

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

    We carried out a theoretical evaluation of the contribution of Asymptotic Giant Branch (AGB) stars to some short-lived (10(exp 6) less than or equal to Tau-bar less than or equal to 2 x 10(exp 7) yr) isotopes in the Interstellar Medium (ISM) and in the early solar system using stellar model calculations for thermally pulsing evolutionary phases of low-mass stars. The yields of s-process nuclei in the convective He-shell for different neutron exposures tau(sub 0) were obtained, and AGB stars were shown to produce several radioactive nuclei (especially Pd-107, Pb-205, Fe-60, Zr-93, Tc-99, Cs-135, and Hf-182) in diferent amounts. Assuming either contamination of the solar nebula from a single AGB star or models for continuous injection and mixing from many stars into the ISM, we calculate the ratios of radioactive to stable nuclei at the epoch of the Sun's formation. The dilution factor between the AGB ejecta and the early solar system matter is obtained by matching the observed Pd-107/Pd-108 and depends on the value of tau(sub 0). It is found that small masses M(sub He) of He-shell material (10(exp -4)-10(exp -7) solar mass) enriched in s-process nuclei are sufficient to contaminate 1 solar mass of the ISM to produce the Pd-107 found in the early solar system. Predictions are made for all of the other radioactive isotopes. The optimal model to explain several observed radioactive species at different states of the proto-solar nebula involves a single AGB star with a low neutron exposure (tau(sub 0) = 0.03 mbarn(sup -1)) which contaminated the cloud with a dilution factor of M(sub He)/solar mass approximately 1.5 x 10(exp -4). This will also contribute newly synthesized stable s-process nuclei in the amount of approximately 10(exp -4) of their abundances already present in the proto-solar cloud. Variations in the degree of homogenization (approximately 30%) of the injected material may account for some of the small general isotopic anomalies found in meteorites. It is

  7. 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.

  8. New light on Galactic post-asymptotic giant branch stars - I. First distance catalogue

    NASA Astrophysics Data System (ADS)

    Vickers, Shane B.; Frew, David J.; Parker, Quentin A.; Bojičić, Ivan S.

    2015-02-01

    We have commenced a detailed analysis of the known sample of Galactic post-asymptotic giant branch (PAGB) objects compiled in the Toruń catalogue of Szczerba et al., and present, for the first time, homogeneously derived distance determinations for the 209 likely and 87 possible catalogued PAGB stars from that compilation. Knowing distances are essential in determining meaningful physical characteristics for these sources and this has been difficult to determine for most objects previously. The distances were determined by modelling their spectral energy distributions (SEDs) with multiple blackbody curves, and integrating under the overall fit to determine the total distance-dependent flux. This approach was undertaken for consistency as precise spectral types, needed for more detailed fitting, were unknown in the majority of cases. The SED method works because the luminosity of these central stars is very nearly constant from the tip of the AGB phase to the beginning of the white dwarf cooling track. This then enables us to use a standard-candle luminosity to estimate the SED distances. For Galactic thin-disc PAGB objects, we use three luminosity bins based on typical observational characteristics, ranging between 3500 and 12 000 L⊙. We further adopt a default luminosity of 4000 L⊙ for bulge objects and 1700 L⊙ for the thick-disc and halo objects. We have also applied the above technique to a further sample of 54 related nebulae not in the current edition of the Toruń catalogue. In a follow-up paper, we will estimate distances to the subset of RV Tauri variables using empirical period-luminosity relations, and to the R CrB stars, allowing a population comparison of these objects with the other subclasses of PAGB stars for the first time.

  9. The Contribution of Thermally-Pulsing Asymptotic Giant Branch and Red Supergiant Starts to the Luminosities of the Magellanic Clouds at 1-24 micrometers

    NASA Technical Reports Server (NTRS)

    Melbourne, J.; Boyer, Martha L.

    2013-01-01

    We present the near-through mid-infrared flux contribution of thermally-pulsing asymptotic giant branch (TP-AGB) and massive red supergiant (RSG) stars to the luminosities of the Large and Small Magellanic Clouds (LMC and SMC, respectively). Combined, the peak contribution from these cool evolved stars occurs at approx 3 - 4 micron, where they produce 32% of the SMC light, and 25% of the LMC flux. The TP-AGB star contribution also peaks at approx 3 - 4 micron and amounts to 21% in both galaxies. The contribution from RSG stars peaks at shorter wavelengths, 2.2 micron, where they provide 11% of the SMC flux, and 7% for the LMC. Both TP-AGB and RSG stars are short lived, and thus potentially impose a large stochastic scatter on the near-IR derived mass-to-light (M/L) ratios of galaxies at rest-frame 1 - 4 micron. To minimize their impact on stellar mass estimates, one can use the M/L ratio at shorter wavelengths (e.g., at 0.8 - 1 micron). At longer wavelengths (much > 8 micron), emission from dust in the interstellar medium dominates the flux. In the LMC, which shows strong polycyclic aromatic hydrocarbon (PAH) emission at 8 micron, TP-AGB and RSG contribute less than 4% of the 8 micron flux. However, 19% of the SMC 8 micron flux is from evolved stars, nearly half of which is produced by the rarest, dustiest, carbon-rich TP-AGB stars. Thus, star formation rates of galaxies, based on an 8 micron flux (e.g., observed-frame 24 micron at z = 2), may be biased modestly high, especially for galaxies with little PAH emission.

  10. THE CONTRIBUTION OF THERMALLY-PULSING ASYMPTOTIC GIANT BRANCH AND RED SUPERGIANT STARS TO THE LUMINOSITIES OF THE MAGELLANIC CLOUDS AT 1-24 {mu}m

    SciTech Connect

    Melbourne, J.; Boyer, Martha L. E-mail: martha.l.boyer@nasa.gov

    2013-02-10

    We present the near-through mid-infrared flux contribution of thermally-pulsing asymptotic giant branch (TP-AGB) and massive red supergiant (RSG) stars to the luminosities of the Large and Small Magellanic Clouds (LMC and SMC, respectively). Combined, the peak contribution from these cool evolved stars occurs at {approx}3-4 {mu}m, where they produce 32% of the SMC light, and 25% of the LMC flux. The TP-AGB star contribution also peaks at {approx}3-4 {mu}m and amounts to 21% in both galaxies. The contribution from RSG stars peaks at shorter wavelengths, 2.2 {mu}m, where they provide 11% of the SMC flux, and 7% for the LMC. Both TP-AGB and RSG stars are short lived, and thus potentially impose a large stochastic scatter on the near-IR derived mass-to-light (M/L) ratios of galaxies at rest-frame 1-4 {mu}m. To minimize their impact on stellar mass estimates, one can use the M/L ratio at shorter wavelengths (e.g., at 0.8-1 {mu}m). At longer wavelengths ({>=}8 {mu}m), emission from dust in the interstellar medium dominates the flux. In the LMC, which shows strong polycyclic aromatic hydrocarbon (PAH) emission at 8 {mu}m, TP-AGB and RSG contribute less than 4% of the 8 {mu}m flux. However, 19% of the SMC 8 {mu}m flux is from evolved stars, nearly half of which is produced by the rarest, dustiest, carbon-rich TP-AGB stars. Thus, star formation rates of galaxies, based on an 8 {mu}m flux (e.g., observed-frame 24 {mu}m at z = 2), may be biased modestly high, especially for galaxies with little PAH emission.

  11. On Carbon Burning in Super Asymptotic Giant Branch Stars

    NASA Astrophysics Data System (ADS)

    Farmer, R.; Fields, C. E.; Timmes, F. X.

    2015-07-01

    We explore the detailed and broad properties of carbon burning in Super Asymptotic Giant Branch (SAGB) stars with 2755 MESA stellar evolution models. The location of first carbon ignition, quenching location of the carbon-burning flames and flashes, angular frequency of the carbon core, and carbon core mass are studied as a function of the zero-age main sequence (ZAMS) mass, initial rotation rate, and mixing parameters such as convective overshoot, semiconvection, thermohaline, and angular momentum transport. In general terms, we find that these properties of carbon burning in SAGB models are not a strong function of the initial rotation profile, but are a sensitive function of the overshoot parameter. We quasi-analytically derive an approximate ignition density, ρign ≈ 2.1 × 106 g cm-3, to predict the location of first carbon ignition in models that ignite carbon off-center. We also find that overshoot moves the ZAMS mass boundaries where off-center carbon ignition occurs at a nearly uniform rate of ΔMZAMS/Δfov ≈ 1.6 {M}⊙ . For zero overshoot, fov = 0.0, our models in the ZAMS mass range ≈8.9-11 {M}⊙ show off-center carbon ignition. For canonical amounts of overshooting, fov = 0.016, the off-center carbon ignition range shifts to ≈7.2-8.8 {M}⊙ . Only systems with fov ≥ 0.01 and ZAMS mass ≈7.2-8.0 {M}⊙ show carbon burning is quenched a significant distance from the center. These results suggest a careful assessment of overshoot modeling approximations on claims that carbon burning quenches an appreciable distance from the center of the carbon core.

  12. A H I IMAGING SURVEY OF ASYMPTOTIC GIANT BRANCH STARS

    SciTech Connect

    Matthews, L. D.; Le Bertre, T.; Gerard, E.; Johnson, M. C.

    2013-04-15

    We present an imaging study of a sample of eight asymptotic giant branch stars in the H I 21 cm line. Using observations from the Very Large Array, we have unambiguously detected H I emission associated with the extended circumstellar envelopes of six of the targets. The detected H I masses range from M{sub H{sub I}} Almost-Equal-To 0.015-0.055 M{sub s}un. The H I morphologies and kinematics are diverse, but in all cases appear to be significantly influenced by the interaction between the circumstellar envelope and the surrounding medium. Four stars (RX Lep, Y UMa, Y CVn, and V1942 Sgr) are surrounded by detached H I shells ranging from 0.36 to 0.76 pc across. We interpret these shells as resulting from material entrained in a stellar outflow being abruptly slowed at a termination shock where it meets the local medium. RX Lep and TX Psc, two stars with moderately high space velocities (V{sub space} > 56 km s{sup -1}), exhibit extended gaseous wakes ({approx}0.3 and 0.6 pc in the plane of the sky), trailing their motion through space. The other detected star, R Peg, displays a peculiar ''horseshoe-shaped'' H I morphology with emission extended on scales up to {approx}1.7 pc; in this case, the circumstellar debris may have been distorted by transverse flows in the local interstellar medium. We briefly discuss our new results in the context of the entire sample of evolved stars that has been imaged in H I to date.

  13. Nucleosynthesis in Electron Capture Supernovae of Asymptotic Giant Branch Stars

    NASA Astrophysics Data System (ADS)

    Wanajo, S.; Nomoto, K.; Janka, H.-T.; Kitaura, F. S.; Müller, B.

    2009-04-01

    We examine nucleosynthesis in the electron capture supernovae of progenitor asymptotic giant branch stars with an O-Ne-Mg core (with the initial stellar mass of 8.8 M sun). Thermodynamic trajectories for the first 810 ms after core bounce are taken from a recent state-of-the-art hydrodynamic simulation. The presented nucleosynthesis results are characterized by a number of distinct features that are not shared with those of other supernovae from the collapse of stars with iron core (with initial stellar masses of more than 10 M sun). First is the small amount of 56Ni (0.002-0.004 M sun) in the ejecta, which can be an explanation for the observed properties of faint supernovae such as SNe 2008S and 1997D. In addition, the large Ni/Fe ratio is in reasonable agreement with the spectroscopic result of the Crab nebula (the relic of SN 1054). Second is the large production of 64Zn, 70Ge, light p-nuclei (74Se, 78Kr, 84Sr, and 92Mo), and in particular, 90Zr, which originates from the low Ye (0.46-0.49, the number of electrons per nucleon) ejecta. We find, however, that only a 1%-2% increase of the minimum Ye moderates the overproduction of 90Zr. In contrast, the production of 64Zn is fairly robust against a small variation of Ye . This provides the upper limit of the occurrence of this type of events to be about 30% of all core-collapse supernovae.

  14. The s-process in low-metallicity stars - II. Interpretation of high-resolution spectroscopic observations with asymptotic giant branch models

    NASA Astrophysics Data System (ADS)

    Bisterzo, S.; Gallino, R.; Straniero, O.; Cristallo, S.; Käppeler, F.

    2011-11-01

    High-resolution spectroscopic observations of 100 metal-poor carbon and s-rich stars (CEMP-s) collected from the literature are compared with the theoretical nucleosynthesis models of the asymptotic giant branch (AGB) presented in Paper I (MAGBini= 1.3, 1.4, 1.5, 2 M⊙, - 3.6 ≲ [ Fe/H ] ≲- 1.5). The s-process enhancement detected in these objects is associated with binary systems: the more massive companion evolved faster through the thermally pulsing AGB phase (TP-AGB), synthesizing s-elements in the inner He intershell, which are partly dredged up to the surface during the third dredge-up (TDU) episode. The secondary observed low-mass companion became CEMP-s by the mass transfer of C- and s-rich material from the primary AGB. We analyse the light elements C, N, O, Na and Mg, as well as the two s-process indicators, [hs/ls] (where ls = is the the light-s peak at N = 50 and hs = the heavy-s peak at N = 82) and [Pb/hs]. We distinguish between CEMP-s with high s-process enhancement, [hs/Fe] >rsim 1.5 (CEMP-sII), and mild s-process enhanced stars, [hs/Fe] < 1.5 (CEMP-sI). To interpret the observations, a range of s-process efficiencies at any given metallicity is necessary. This is confirmed by the high spread observed in [Pb/hs] (˜2 dex). A degeneration of solutions is found with some exceptions: most main-sequence CEMP-sII stars with low [Na/Fe] can only be interpreted with MAGBini= 1.3-1.4 M⊙. Giants having suffered the first dredge-up (FDU) need a dilution >rsim1 dex (dil is defined as the mass of the convective envelope of the observed star, Mobs★, over the material transferred from the AGB to the companion, MtransAGB). Then AGB models with higher AGB initial masses (MAGBini= 1.5-2 M⊙) are adopted to interpret CEMP-sII giants. In general, solutions with AGB models in the mass range MAGBini= 1.3-2 M⊙ and different dilution factors are found for CEMP-sI stars. About half of the CEMP-s stars with europium measurements show a high r

  15. 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.

  16. 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

  17. 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.

  18. Nucleosynthesis in Asymptotic Giant Branch Stars: Relevance for Galactic Enrichment and Solar System Formation

    NASA Astrophysics Data System (ADS)

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

    We present a review of nucleosynthesis in AGB stars outlining the development of theoretical models and their relationship to observations. We focus on the new high resolution codes with improved opacities, which recently succeeded in accounting for the third dredge-up. This opens the possibility of understanding low luminosity C stars (enriched in s-elements) as the normal outcome of AGB evolution, characterized by production of 12C and neutron-rich nuclei in the He intershell and by mass loss from strong stellar winds. Neutron captures in AGB stars are driven by two reactions: 13C([α],n)16O, which provides the bulk of the neutron flux at low neutron densities (Nn [<=] 107 n/cm3), and 22Ne([α],n)25Mg, which is mildly activated at higher temperatures and mainly affects the production of s-nuclei depending on reaction branchings. The first reaction is now known to occur in the radiative interpulse phase, immediately below the region previously homogenized by third dredge-up. The second reaction occurs during the convective thermal pulses. The resulting nucleosynthesis phenomena are rather complex and rule out any analytical approximation (exponential distribution of neutron fluences). Nucleosynthesis in AGB stars, modeled at different metallicities, account for several observational constraints, coming from a wide spectrum of sources: evolved red giants rich in s-elements, unevolved stars at different metallicities, presolar grains recovered from meteorites, and the abundances of s-process isotopes in the solar system. In particular, a good reproduction of the solar system main component is obtained as a result of Galactic chemical evolution that mixes the outputs of AGB stars of different stellar generations, born with different metallicities and producing different patterns of s-process nuclei. The main solar s-process pattern is thus not considered to be the result of a standard archetypal s-process occurring in all stars. Concerning the 13C neutron source, its

  19. A proposed direct measurement of cross section at Gamow window for key reaction 19F(p,α) 16O in Asymptotic Giant Branch stars with a planned accelerator in CJPL

    NASA Astrophysics Data System (ADS)

    He, JianJun; Xu, ShiWei; Ma, ShaoBo; Hu, Jun; Zhang, LiYong; Fu, ChangBo; Zhang, NingTao; Lian, Gang; Su, Jun; Li, YunJu; Yan, ShengQuan; Shen, YangPing; Hou, SuQing; Jia, BaoLu; Zhang, Tao; Zhang, XiaoPeng; Guo, Bing; Kubono, Shigeru; Liu, WeiPing

    2016-05-01

    In 2014, the National Natural Science Foundation of China (NSFC) approved the Jinping Underground Nuclear Astrophysics laboratory (JUNA) project, which aims at direct cross-section measurements of four key stellar nuclear reactions right down to the Gamow windows. In order to solve the observed fluorine overabundances in Asymptotic Giant Branch (AGB) stars, measuring the key 19F(p,α)16O reaction at effective burning energies (i.e., at Gamow window) is established as one of the scientific research sub-projects. The present paper describes this sub-project in details, including motivation, status, experimental setup, yield and background estimation, aboveground test, as well as other relevant reactions.

  20. Inverse Kinematic Study of the (26g)Al(d,p)(27)Al Reaction and Implications for Destruction of (26)Al in Wolf-Rayet and Asymptotic Giant Branch Stars.

    PubMed

    Margerin, V; Lotay, G; Woods, P J; Aliotta, M; Christian, G; Davids, B; Davinson, T; Doherty, D T; Fallis, J; Howell, D; Kirsebom, O S; Mountford, D J; Rojas, A; Ruiz, C; Tostevin, J A

    2015-08-01

    In Wolf-Rayet and asymptotic giant branch (AGB) stars, the (26g)Al(p,γ)(27)Si reaction is expected to govern the destruction of the cosmic γ-ray emitting nucleus (26)Al. The rate of this reaction, however, is highly uncertain due to the unknown properties of key resonances in the temperature regime of hydrogen burning. We present a high-resolution inverse kinematic study of the (26g)Al(d,p)(27)Al reaction as a method for constraining the strengths of key astrophysical resonances in the (26g)Al(p,γ)(27)Si reaction. In particular, the results indicate that the resonance at E(r)=127  keV in (27)Si determines the entire (26g)Al(p,γ)(27)Si reaction rate over almost the complete temperature range of Wolf-Rayet stars and AGB stars. PMID:26296114

  1. 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

    We model multi-wavelength broadband UBVIJHK{sub s} and Spitzer IRAC and MIPS photometry and Infrared Spectrograph spectra from the SAGE and SAGE-Spectroscopy observing programs of two oxygen-rich asymptotic giant branch (O-rich AGB) stars in the Large Magellanic Cloud (LMC) using radiative transfer (RT) models of dust shells around stars. We chose a star from each of the bright and faint O-rich AGB populations found by earlier studies of the SAGE sample in order to derive a baseline set of dust properties to be used in the construction of an extensive grid of RT models of the O-rich AGB stars found in the SAGE surveys. From the bright O-rich AGB population, we chose HV 5715, and from the faint O-rich AGB population we chose SSTISAGE1C J052206.92-715017.6 (SSTSAGE052206). We found the complex indices of refraction of oxygen-deficient silicates from Ossenkopf et al. and a power law with exponential decay grain size distribution like what Kim et al. used but with {gamma} of -3.5, a {sub min} of 0.01 {mu}m, and a {sub 0} of 0.1 {mu}m to be reasonable dust properties for these models. There is a slight indication that the dust around the faint O-rich AGB may be more silica-rich than that around the bright O-rich AGB. Simple models of gas emission suggest a relatively extended gas envelope for the faint O-rich AGB star modeled, consistent with the relatively large dust shell inner radius for the same model. Our models of the data require the luminosity of SSTSAGE052206 and HV 5715 to be {approx}5100 L {sub sun} and {approx}36,000 L {sub sun}, respectively. This, combined with the stellar effective temperatures of 3700 K and 3500 K, respectively, that we find best fit the optical and near-infrared data, suggests stellar masses of {approx}3 M {sub sun} and {approx}7 M {sub sun}. This, in turn, suggests that HV 5715 is undergoing hot-bottom burning and that SSTSAGE052206 is not. Our models of SSTSAGE052206 and HV 5715 require dust shells of inner radius {approx}17 and

  2. Shell and explosive hydrogen burning. Nuclear reaction rates for hydrogen burning in RGB, AGB and Novae

    NASA Astrophysics Data System (ADS)

    Boeltzig, A.; Bruno, C. G.; Cavanna, F.; Cristallo, S.; Davinson, T.; Depalo, R.; deBoer, R. J.; Di Leva, A.; Ferraro, F.; Imbriani, G.; Marigo, P.; Terrasi, F.; Wiescher, M.

    2016-04-01

    The nucleosynthesis of light elements, from helium up to silicon, mainly occurs in Red Giant and Asymptotic Giant Branch stars and Novae. The relative abundances of the synthesized nuclides critically depend on the rates of the nuclear processes involved, often through non-trivial reaction chains, combined with complex mixing mechanisms. In this paper, we summarize the contributions made by LUNA experiments in furthering our understanding of nuclear reaction rates necessary for modeling nucleosynthesis in AGB stars and Novae explosions.

  3. FAR-INFRARED IMAGING OF POST-ASYMPTOTIC GIANT BRANCH STARS AND (PROTO)-PLANETARY NEBULAE WITH THE AKARI FAR-INFRARED SURVEYOR

    SciTech Connect

    Cox, N. L. J.; Garcia-Hernandez, D. A.; Manchado, A.

    2011-04-15

    By tracing the distribution of cool dust in the extended envelopes of post-asymptotic giant branch stars and (proto)-planetary nebulae ((P)PNe), we aim to recover, or constrain, the mass-loss history experienced by these stars in their recent past. The Far-Infrared Surveyor (FIS) instrument on board the AKARI satellite was used to obtain far-infrared maps for a selected sample of post-AGB stars and (P)PNe. We derived flux densities (aperture photometry) for 13 post-AGB stars and (P)PNe at four far-infrared wavelengths (65, 90, 140, and 160 {mu}m). Radial (azimuthally averaged) profiles are used to investigate the presence of extended emission from cool dust. No (detached) extended emission is detected for any target in our sample at levels significant with respect to background and cirrus emission. Only IRAS 21046+4739 reveals tentative excess emission between 30'' and 130''. Estimates of the total dust and gas mass from the obtained maps indicate that the envelope masses of these stars should be large in order to be detected with the AKARI FIS. Imaging with higher sensitivity and higher spatial resolution is needed to detect and resolve, if present, any cool compact or extended emission associated with these evolved stars.

  4. Maser and infrared studies of oxygen-rich late/post-asymptotic giant branch stars and water fountains: development of a new identification method

    SciTech Connect

    Yung, Bosco H. K.; Nakashima, Jun-ichi; Henkel, Christian

    2014-10-10

    We explored an efficient method to identify evolved stars with oxygen-rich envelopes in the late asymptotic giant branch (AGB) or post-AGB phase of stellar evolution, which include a rare class of objects—the 'water fountains (WF)'. Our method considers the OH and H{sub 2}O maser spectra, the near-infrared Q-parameters (these are color indices accounting for the effect of extinction), and far-infrared AKARI colors. Here we first present the results of a new survey on OH and H{sub 2}O masers. There were 108 color-selected objects: 53 of them were observed in the three OH maser lines (1612, 1665, and 1667 MHz), with 24 detections (16 new for 1612 MHz); and 106 of them were observed in the H{sub 2}O maser line (22 GHz), with 24 detections (12 new). We identify a new potential WF source, IRAS 19356+0754, with large velocity coverages of both OH and H{sub 2}O maser emission. In addition, several objects with high-velocity OH maser emission are reported for the first time. The Q-parameters as well as the infrared [09]–[18] and [18]–[65] AKARI colors of the surveyed objects are then calculated. We suggest that these infrared properties are effective in isolating aspherical from spherical objects, but the morphology may not necessarily be related to the evolutionary status. Nonetheless, by considering altogether the maser and infrared properties, the efficiency of identifying oxygen-rich late/post-AGB stars could be improved.

  5. The s-process in low-metallicity stars - III. Individual analysis of CEMP-s and CEMP-s/r with asymptotic giant branch models

    NASA Astrophysics Data System (ADS)

    Bisterzo, S.; Gallino, R.; Straniero, O.; Cristallo, S.; Käppeler, F.

    2012-05-01

    We provide an individual analysis of 94 carbon-enhanced metal-poor stars showing an s-process enrichment (CEMP-s) collected from the literature. The s-process enhancement observed in these stars is ascribed to mass transfer by stellar winds in a binary system from a more massive companion evolving faster towards the asymptotic giant branch (AGB) phase. The theoretical AGB nucleosynthesis models have been presented in Bisterzo et al. (Paper I of this series). Several CEMP-s show an enhancement in both s- and r-process elements (CEMP-s/r). In order to explain the peculiar abundances observed in CEMP-s/r, we assume that the molecular cloud from which CEMP-s formed was previously enriched in r-elements by supernova pollution. A general discussion and the method adopted in order to interpret the observations have been provided in Bisterzo et al. (Paper II of this series). We present in this paper a detailed study of spectroscopic observations of individual stars. We consider all elements from carbon to bismuth, with particular attention to the three s-process peaks, ls (Y, Zr), hs (La, Nd, Sm) and Pb, and their ratios [hs/ls] and [Pb/hs]. The presence of an initial r-process contribution may be typically evaluated by [La/Eu]. We found possible agreements between theoretical predictions and spectroscopic data. In general, the observed [Na/Fe] (and [Mg/Fe]) provides information on the AGB initial mass, while [hs/ls] and [Pb/hs] are mainly indicators of the s-process efficiency. A range of 13C-pocket strengths are required to interpret the observations. However, major discrepancies between models and observations exist. We highlight star by star the agreements and the main problems encountered and, when possible, we suggest potential indications for further studies. These discrepancies provide starting points of debate for unsolved problems in which spectroscopic and theoretical studies may intervene.

  6. EUROPIUM s-PROCESS SIGNATURE AT CLOSE-TO-SOLAR METALLICITY IN STARDUST SiC GRAINS FROM ASYMPTOTIC GIANT BRANCH STARS

    SciTech Connect

    Avila, Janaina N.; Ireland, Trevor R.; Holden, Peter; Lugaro, Maria; Gyngard, Frank; Zinner, Ernst; Cristallo, Sergio; Rauscher, Thomas

    2013-05-01

    Individual mainstream stardust silicon carbide (SiC) grains and a SiC-enriched bulk sample from the Murchison carbonaceous meteorite have been analyzed by the Sensitive High Resolution Ion Microprobe-Reverse Geometry for Eu isotopes. The mainstream grains are believed to have condensed in the outflows of {approx}1.5-3 M{sub Sun} carbon-rich asymptotic giant branch (AGB) stars with close-to-solar metallicity. The {sup 151}Eu fractions [fr({sup 151}Eu) = {sup 151}Eu/({sup 151}Eu+{sup 153}Eu)] derived from our measurements are compared with previous astronomical observations of carbon-enhanced metal-poor stars enriched in elements made by slow neutron captures (the s-process). Despite the difference in metallicity between the parent stars of the grains and the metal-poor stars, the fr({sup 151}Eu) values derived from our measurements agree well with fr({sup 151}Eu) values derived from astronomical observations. We have also compared the SiC data with theoretical predictions of the evolution of Eu isotopic ratios in the envelope of AGB stars. Because of the low Eu abundances in the SiC grains, the fr({sup 151}Eu) values derived from our measurements show large uncertainties, in most cases being larger than the difference between solar and predicted fr({sup 151}Eu) values. The SiC aggregate yields a fr({sup 151}Eu) value within the range observed in the single grains and provides a more precise result (fr({sup 151}Eu) = 0.54 {+-} 0.03, 95% conf.), but is approximately 12% higher than current s-process predictions. The AGB models can match the SiC data if we use an improved formalism to evaluate the contribution of excited nuclear states in the calculation of the {sup 151}Sm(n, {gamma}) stellar reaction rate.

  7. 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.

  8. 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.

  9. 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.

  10. An extreme paucity of second population AGB stars in the `normal' globular cluster M4

    NASA Astrophysics Data System (ADS)

    MacLean, B. T.; Campbell, S. W.; De Silva, G. M.; Lattanzio, J.; D'Orazi, V.; Simpson, J. D.; Momany, Y.

    2016-07-01

    Galactic globular clusters (GCs) are now known to harbour multiple stellar populations, which are chemically distinct in many light element abundances. It is becoming increasingly clear that asymptotic giant branch (AGB) stars in GCs show different abundance distributions in light elements compared to those in the red giant branch (RGB) and other phases, skewing towards more primordial, field-star-like abundances, which we refer to as subpopulation one (SP1). As part of a larger programme targeting giants in GCs, we obtained high-resolution spectra for a sample of 106 RGB and 15 AGB stars in Messier 4 (NGC 6121) using the 2dF+HERMES facility on the Anglo-Australian Telescope. In this Letter, we report an extreme paucity of AGB stars with [Na/O] >-0.17 in M4, which contrasts with the RGB that has abundances up to [Na/O] =0.55. The AGB abundance distribution is consistent with all AGB stars being from SP1. This result appears to imply that all subpopulation two stars (SP2; Na-rich, O-poor) avoid the AGB phase. This is an unexpected result given M4's horizontal branch morphology - it does not have an extended blue horizontal branch. This is the first abundance study to be performed utilizing the HERMES spectrograph.

  11. An extreme paucity of second population AGB stars in the `normal' globular cluster M4

    NASA Astrophysics Data System (ADS)

    MacLean, B. T.; Campbell, S. W.; De Silva, G. M.; Lattanzio, J.; D'Orazi, V.; Simpson, J. D.; Momany, Y.

    2016-04-01

    Galactic Globular clusters (GCs) are now known to harbour multiple stellar populations, which are chemically distinct in many light element abundances. It is becoming increasingly clear that asymptotic giant branch (AGB) stars in GCs show different abundance distributions in light elements compared to those in the red giant branch (RGB) and other phases, skewing toward more primordial, field-star-like abundances, which we refer to as subpopulation one (SP1). As part of a larger program targeting giants in GCs, we obtained high-resolution spectra for a sample of 106 RGB and 15 AGB stars in Messier 4 (NGC 6121) using the 2dF+HERMES facility on the Anglo-Australian Telescope. In this Letter we report an extreme paucity of AGB stars with [Na/O] >-0.17 in M4, which contrasts with the RGB that has abundances up to [Na/O] =0.55. The AGB abundance distribution is consistent with all AGB stars being from SP1. This result appears to imply that all subpopulation two stars (SP2; Na-rich, O-poor) avoid the AGB phase. This is an unexpected result given M4's horizontal branch morphology - it does not have an extended blue horizontal branch. This is the first abundance study to be performed utilising the HERMES spectrograph.

  12. 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).

  13. 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.

  14. 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.

  15. AGB stars in Leo P and their use as metallicity probes

    NASA Astrophysics Data System (ADS)

    Lee ( ), Chien-Hsiu

    2016-09-01

    Leo P is the most metal-poor yet star-forming galaxy in the local volume, and has the potential to serve as a local counterpart to interpret the properties of distant galaxies in the early universe. We present a comprehensive search of asymptotic giant branch (AGB) stars in Leo P using deep infrared imaging. AGB stars are the major dust contributors; the metal poor nature of Leo P can help to shed light on the dust formation process in very low-metallicity environments, similar to the early Universe. We select and classify oxygen-rich and carbon-rich candidate AGB stars using J - K versus K colour-magnitude diagram. To filter out contaminations from background galaxies, we exploit the high-resolution Hubble Space Telescope imaging and identify 9 oxygen-rich AGBs and 13 carbon-rich AGB stars in Leo P. We then use the ratio of carbon-rich and oxygen-rich AGB stars (C/M ratio) as an indicator of on-site metallicity and derive the global metallicity [Fe/H] = -1.8 dex for Leo P, in good agreement with previous studies using isochrone fitting. Follow-up observations of these Leo P AGB stars in the mid-infrared [e.g. Spitzer, James Webb Space Telescope (JWST)] will be invaluable to measure the dust formation rates using Spectral energy distribution (SED) fitting.

  16. 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.

  17. 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.

  18. THE WIDESPREAD OCCURRENCE OF WATER VAPOR IN THE CIRCUMSTELLAR ENVELOPES OF CARBON-RICH ASYMPTOTIC GIANT BRANCH STARS: FIRST RESULTS FROM A SURVEY WITH HERSCHEL /HIFI

    SciTech Connect

    Neufeld, D. A.; Gonzalez-Alfonso, E.; Melnick, G.; Szczerba, R.; Schmidt, M.; Decin, L.; Alcolea, J.; De Koter, A.; Dominik, C.; Waters, L. B. F. M.; Schoeier, F. L.; Justtanont, K.; Olofsson, H.; Bujarrabal, V.; Planesas, P.; Cernicharo, J.; Teyssier, D.; Marston, A. P.; Menten, K.

    2011-02-01

    We report the preliminary results of a survey for water vapor in a sample of eight C stars with large mid-IR continuum fluxes: V384 Per, CIT 6, V Hya, Y CVn, IRAS 15194-5115, V Cyg, S Cep, and IRC+40540. This survey, performed using the HIFI instrument on board the Herschel Space Observatory, entailed observations of the lowest transitions of both ortho- and para-water: the 556.936 GHz 1{sub 10}-1{sub 01} and 1113.343 GHz 1{sub 11}-0{sub 00} transitions, respectively. Water vapor was unequivocally detected in all eight of the target stars. Prior to this survey, IRC+10216 was the only carbon-rich asymptotic giant branch (AGB) star from which thermal water emissions had been discovered, in that case with the use of the Submillimeter Wave Astronomy Satellite (SWAS). Our results indicate that IRC+10216 is not unusual, except insofar as its proximity to Earth leads to a large line flux that was detectable with SWAS. The water spectral line widths are typically similar to those of CO rotational lines, arguing against the vaporization of a Kuiper Belt analog being the general explanation for water vapor in carbon-rich AGB stars. There is no apparent correlation between the ratio of the integrated water line fluxes to the 6.3 {mu}m continuum flux-a ratio which measures the water outflow rate-and the total mass-loss rate for the stars in our sample.

  19. On the necessity of composition-dependent low-temperature opacity in models of metal-poor asymptotic giant branch stars

    SciTech Connect

    Constantino, Thomas; Campbell, Simon; Lattanzio, John; Gil-Pons, Pilar

    2014-03-20

    The vital importance of composition-dependent low-temperature opacity in low-mass (M ≤ 3 M {sub ☉}) asymptotic giant branch (AGB) stellar models of metallicity Z ≥ 0.001 has recently been demonstrated. Its significance to more metal-poor, intermediate-mass (M ≥ 2.5 M {sub ☉}) models has yet to be investigated. We show that its inclusion in lower-metallicity models ([Fe/H] ≤–2) is essential and that there exists no threshold metallicity below which composition-dependent molecular opacity may be neglected. We find it to be crucial in all intermediate-mass models investigated ([Fe/H] ≤–2 and 2.5 ≤ M/M {sub ☉} ≤ 5), because of the evolution of the surface chemistry, including the orders of magnitude increase in the abundance of molecule-forming species. Its effect on these models mirrors that previously reported for higher-metallicity models—increase in radius, decrease in T {sub eff}, faster mass loss, shorter thermally pulsing AGB lifetime, reduced enrichment in third dredge-up products (by a factor of 3-10), and an increase in the mass limit for hot bottom burning. We show that the evolution of low-metallicity models with composition-dependent low-temperature opacity is relatively independent of initial metal abundance because its contribution to the opacity is far outweighed by changes resulting from dredge-up. Our results imply a significant reduction in the expected number of nitrogen-enhanced metal-poor stars, which may help explain their observed paucity. We note that these findings are partially a product of the macrophysics adopted in our models, in particular, the Vassiliadis and Wood mass loss rate which is strongly dependent on radius.

  20. ON IRON MONOXIDE NANOPARTICLES AS A CARRIER OF THE MYSTERIOUS 21 μm EMISSION FEATURE IN POST-ASYMPTOTIC GIANT BRANCH STARS

    SciTech Connect

    Li, Aigen; Jiang, B. W.; Liu, J. M. E-mail: bjiang@bnu.edu.cn

    2013-11-10

    A prominent mysterious emission feature peaking at ∼20.1 μm—historically known as the '21 μm' feature—is seen in over two dozen Galactic and Magellanic Cloud carbon-rich, post-asymptotic giant branch (post-AGB) stars. The nature of its carrier remains unknown since the first detection of the 21 μm feature in 1989. Over a dozen materials have been suggested as possible carrier candidates. However, none of them has been accepted: they either require too much material (compared to what is available in the circumstellar shells around these post-AGB stars), or exhibit additional emission features that are not seen in these 21 μm sources. Recently, iron monoxide (FeO) nanoparticles seem to be a promising carrier candidate as Fe is an abundant element and FeO emits exclusively at ∼21 μm. In this work, using the proto-typical protoplanetary nebula HD 56126 as a test case, we examine FeO nanoparticles as a carrier for the 21 μm feature by modeling their infrared emission, with FeO being stochastically heated by single stellar photons. We find that FeO emits too broad a 21 μm feature to explain that observed and the Fe abundance required to be locked up in FeO exceeds what is available in HD 56126. We therefore conclude that FeO nanoparticles are not likely to be responsible for the 21 μm feature.

  1. IRAS 17423-1755 (HEN 3-1475) REVISITED: AN O-RICH HIGH-MASS POST-ASYMPTOTIC GIANT BRANCH STAR

    SciTech Connect

    Manteiga, M.; GarcIa-Hernandez, D. A.; Manchado, A.; GarcIa-Lario, P.

    2011-03-15

    The high-resolution (R {approx} 600) Spitzer/IRS spectrum of the bipolar protoplanetary nebula (PN) IRAS 17423-1755 is presented in order to clarify the dominant chemistry (C-rich versus O-rich) of its circumstellar envelope as well as to constrain its evolutionary stage. The high-quality Spitzer/IRS spectrum shows weak 9.7 {mu}m absorption from amorphous silicates. This confirms for the first time the O-rich nature of IRAS 17423-1755 in contradiction to a previous C-rich classification, which was based on the wrong identification of the strong 3.1 {mu}m absorption feature seen in the Infrared Space Observatory spectrum as due to acetylene (C{sub 2}H{sub 2}). The high-resolution Spitzer/IRS spectrum displays a complete lack of C-rich mid-IR features such as molecular absorption features (e.g., 13.7 {mu}m C{sub 2}H{sub 2}, 14.0 {mu}m HCN, etc.) or the classical polycyclic aromatic hydrocarbon infrared emission bands. Thus, the strong 3.1 {mu}m absorption band toward IRAS 17423-1755 has to be identified as water ice. In addition, an [Ne II] nebular emission line at 12.8 {mu}m is clearly detected, indicating that the ionization of its central region may be already started. The spectral energy distribution in the infrared ({approx}2-200 {mu}m) and other observational properties of IRAS 17423-1755 are discussed in comparison with the similar post-asymptotic giant branch (AGB) objects IRAS 19343+2926 and IRAS 17393-2727. We conclude that IRAS 17423-1755 is an O-rich high-mass post-AGB object that represents a link between OH/IR stars with extreme outflows and highly bipolar PN.

  2. POST ASYMPTOTIC GIANT BRANCH BIPOLAR REFLECTION NEBULAE: RESULT OF DYNAMICAL EJECTION OR SELECTIVE ILLUMINATION?

    SciTech Connect

    Koning, N.; Kwok, Sun; Steffen, W. E-mail: sunkwok@hku.hk

    2013-03-10

    A model for post asymptotic giant branch bipolar reflection nebulae has been constructed based on a pair of evacuated cavities in a spherical dust envelope. Many of the observed features of bipolar nebulae, including filled bipolar lobes, an equatorial torus, searchlight beams, and a bright central light source, can be reproduced. The effects on orientation and dust densities are studied and comparisons with some observed examples are offered. We suggest that many observed properties of bipolar nebulae are the result of optical effects and any physical modeling of these nebulae has to take these factors into consideration.

  3. 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

  4. HERSCHEL /HIFI OBSERVATIONS OF IRC+10216: WATER VAPOR IN THE INNER ENVELOPE OF A CARBON-RICH ASYMPTOTIC GIANT BRANCH STAR

    SciTech Connect

    Neufeld, David A.; Gonzalez-Alfonso, Eduardo; Melnick, Gary J.; Szczerba, Ryszard; Schmidt, Miroslaw; Decin, Leen; De Koter, Alex; Schoeier, Fredrik; Cernicharo, Jose

    2011-02-01

    We report the results of observations of 10 rotational transitions of water vapor toward the carbon-rich asymptotic giant branch (AGB) star IRC+10216 (CW Leonis), carried out with Herschel's HIFI instrument. Each transition was securely detected by means of observations using the dual beam switch mode of HIFI. The measured line ratios imply that water vapor is present in the inner outflow at small distances ({<=}few x 10{sup 14} cm) from the star, confirming recent results reported by Decin et al. from observations with Herschel's PACS and SPIRE instruments. This finding definitively rules out the hypothesis that the observed water results from the vaporization of small icy objects in circular orbits. The origin of water within the dense C-rich envelope of IRC+10216 remains poorly understood. We derive upper limits on the H{sup 17}{sub 2}O/H{sup 16}{sub 2}O and H{sup 18}{sub 2}O/H{sup 16}{sub 2}O isotopic abundance ratios of {approx}5 x 10{sup -3} (3{sigma}), providing additional constraints on models for the origin of the water vapor in IRC+10216.

  5. Herschel/HIFI Observations of IRC+10216: Water Vapor in the Inner Envelope of a Carbon-rich Asymptotic Giant Branch Star

    NASA Astrophysics Data System (ADS)

    Neufeld, David A.; González-Alfonso, Eduardo; Melnick, Gary J.; Szczerba, Ryszard; Schmidt, Miroslaw; Decin, Leen; de Koter, Alex; Schöier, Fredrik; Cernicharo, José

    2011-02-01

    We report the results of observations of 10 rotational transitions of water vapor toward the carbon-rich asymptotic giant branch (AGB) star IRC+10216 (CW Leonis), carried out with Herschel's HIFI instrument. Each transition was securely detected by means of observations using the dual beam switch mode of HIFI. The measured line ratios imply that water vapor is present in the inner outflow at small distances (<=few × 1014 cm) from the star, confirming recent results reported by Decin et al. from observations with Herschel's PACS and SPIRE instruments. This finding definitively rules out the hypothesis that the observed water results from the vaporization of small icy objects in circular orbits. The origin of water within the dense C-rich envelope of IRC+10216 remains poorly understood. We derive upper limits on the H17 2O/H16 2O and H18 2O/H16 2O isotopic abundance ratios of ~5 × 10-3 (3σ), providing additional constraints on models for the origin of the water vapor in IRC+10216. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

  6. AGB sodium abundances in the globular cluster 47 Tucanae (NGC 104)

    SciTech Connect

    Johnson, Christian I.; McDonald, Iain; Zijlstra, Albert A. E-mail: iain.mcdonald-2@manchester.ac.uk; and others

    2015-02-01

    A recent analysis comparing the [Na/Fe] distributions of red giant branch (RGB) and asymptotic giant branch (AGB) stars in the Galactic globular cluster NGC 6752 found that the ratio of Na-poor to Na-rich stars changes from 30:70 on the RGB to 100:0 on the AGB. The surprising paucity of Na-rich stars on the AGB in NGC 6752 warrants additional investigations to determine if the failure of a significant fraction of stars to ascend the AGB is an attribute common to all globular clusters. Therefore, we present radial velocities, [Fe/H], and [Na/Fe] abundances for 35 AGB stars in the Galactic globular cluster 47 Tucanae (47 Tuc; NGC 104), and compare the AGB [Na/Fe] distribution with a similar RGB sample published previously. The abundances and velocities were derived from high-resolution spectra obtained with the Michigan/Magellan Fiber System and MSpec spectrograph on the Magellan–Clay 6.5 m telescope. We find the average heliocentric radial velocity and [Fe/H] values to be 〈RV{sub helio.}〉 = −18.56 km s{sup −1} (σ = 10.21 km s{sup −1}) and 〈[Fe/H]〉 = −0.68 (σ = 0.08), respectively, in agreement with previous literature estimates. The average [Na/Fe] abundance is 0.12 dex lower in the 47 Tuc AGB sample compared to the RGB sample, and the ratio of Na-poor to Na-rich stars is 63:37 on the AGB and 45:55 on the RGB. However, in contrast to NGC 6752, the two 47 Tuc populations have nearly identical [Na/Fe] dispersion and interquartile range values. The data presented here suggest that only a small fraction (≲20%) of Na-rich stars in 47 Tuc may fail to ascend the AGB, which is a similar result to that observed in M13. Regardless of the cause for the lower average [Na/Fe] abundance in AGB stars, we find that Na-poor stars and at least some Na-rich stars in 47 Tuc evolve through the early AGB phase. The contrasting behavior of Na-rich stars in 47 Tuc and NGC 6752 suggests that the RGB [Na/Fe] abundance alone is insufficient for predicting if a star will

  7. 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.

  8. 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.

  9. The identification of extreme asymptotic giant branch stars and red supergiants in M33 with 24 μm variability

    SciTech Connect

    Montiel, Edward J.; Clayton, Geoffrey C.; Johnson, Christopher B.; Srinivasan, Sundar; Engelbracht, Charles W.

    2015-02-01

    We present the first detection of 24 μm variability in 24 sources in the Local Group galaxy M33. These results are based on 4 epochs of Multiband Imaging Photometer for Spitzer observations, which are irregularly spaced over ∼750 days. We find that these sources are constrained exclusively to the Holmberg radius of the galaxy, which increases their chances of being members of M33. We have constructed spectral energy distributions (SEDs) ranging from the optical to the submillimeter to investigate the nature of these objects. We find that 23 of our objects are most likely heavily self-obscured, evolved stars, while the remaining source is the Giant H ii region, NGC 604. We believe that the observed variability is the intrinsic variability of the central star reprocessed through their circumstellar dust shells. Radiative transfer modeling was carried out to determine their likely chemical composition, luminosity, and dust production rate (DPR). As a sample, our modeling has determined an average luminosity of (3.8±0.9)×10{sup 4} L{sub ⊙} and a total DPR of (2.3±0.1)×10{sup −5} M{sub ⊙} yr{sup −1}. Most of the sources, given the high DPRs and short wavelength obscuration, are likely extreme asymptotic giant branch (XAGB) stars. Five of the sources are found to have luminosities above the classical AGB limit (M{sub bol} <−7.1 mag, L > 54,000 L{sub ⊙}), which classifies them as probable red supergiants (RSGs). Almost all of the sources are classified as oxygen-rich. As also seen in the LMC, a significant fraction of the dust in M33 is produced by a handful of XAGB and RSG stars.

  10. On the introduction of 17O+p reaction rates evaluated through the THM in AGB nucleosynthesis calculations

    NASA Astrophysics Data System (ADS)

    Palmerini, S.; Sergi, M. L.; La Cognata, M.; Lamia, L.; Pizzone, R. G.; Spitaleri, C.

    2014-05-01

    The rates for the 17O(p,αα14N, 17O(p,α)18F and 18O(p,α)15N reactions deduced trough the Trojan Horse Method (THM) have been introduced into a state-of-the-art asymptotic giant branch (AGB) models for proton-capture nucleosynthesis and cool bottom process. The predicted abundances have been compared with isotopic compositions provided by geochemical analysis of presolar grains. As a result, an improved agreement is found between the models and the isotopic mix of oxide grains of AGB origins, whose composition is the signature of low-temperature proton-capture nucleosynthesis.

  11. AGB Stars in Galactic Globular Clusters: Are They Really Chemically Distinct from Their Fellow RGB and HB Stars?

    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.

    2011-09-01

    The handful of available observations of asymptotic giant branch (AGB) stars in Galactic globular clusters (GCs) suggest that the globular cluster AGB populations are dominated by cyanogen-weak (CN-weak) stars. This contrasts strongly with the distributions on the red giant branch (RGB) and other populations, which often show a 50:50 bimodality in CN band strength. If this is true 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 globular clusters. We have obtained medium resolution spectra for about 250 AGB stars across 9 Galactic globular clusters (NGC 1851, NGC 288, NGC 362, NGC 6752, M2, M4, M5, M10, and 47 Tuc) using the multi-object spectrograph on the Anglo-Australian Telescope (2df/AAOmega). In this contribution we present some preliminary findings of the study, in particular for the second-parameter pair NGC 288 and NGC 362.

  12. Optical Properties of Amorphous Alumina Dust in the Envelopes around O-Rich AGB Stars

    NASA Astrophysics Data System (ADS)

    Suh, Kyung-Won

    2016-08-01

    We investigate optical properties of amorphous alumina (Al_2O_3) dust grains in the envelopes around O-rich asymptotic giant branch (AGB) stars using laboratory measured optical data. We derive the optical constants of amorphous alumina over a wide wavelength range that satisfy the Kramers-Kronig relation and reproduce the laboratory data. Using the amorphous alumina and silicate dust, we compare the radiative transfer model results with the observed spectral energy distributions. Comparing the theoretical models with observations on various IR two-color diagrams for a large sample of O-rich AGB stars, we find that the amorphous alumina dust (about 10-40%) mixed with amorphous silicate better models the observed points for the O-rich AGB stars with thin dust envelopes.

  13. Silicate and related dust emission in stars on the asymptotic giant branch

    NASA Technical Reports Server (NTRS)

    Sloan, G. C.; Price, S. D.; Little-Marenin, I. R.; Levan, P. G.

    1995-01-01

    The Low-Resolution Spectrometer (LRS) on the Infrared Astronomical Satellite (IRAS) produced a rich set of spectra from oxygen-rich circumstellar dust shells. Little-Marenin and Little found that in addition to the classic 10 micron emission feature due to silicate dust, many oxygen-rich shells also produce components at 11 and 13 microns. Some shells exhibit only a broad, low-contrast feature which peaks longward of 11 microns and has been attributed to alumina dust. We have modified the classification method of Little-Marenin and Little, applied it to a large sample of bright oxygen-rich variables on the asymptotic giant branch, and undertaken a study of the 13 micron emission feature and the sources which produce it. We present some of the results of these studies.

  14. The Mathematical Model of the Photometric Variability and Classification of Semiregular Pulsating Asymptotic Giants Branch Stars

    NASA Astrophysics Data System (ADS)

    Kudashkina, L. S.

    The modern review of the stars which are located at the position of asymptotic giant branch at the HRdiagram is presented. The most interesting problems connected to these objects are noted, as well as attention is paid to classification and to the evolutionary status. We provided mathematical modeling of the mean light curve of the semiregular supergiant S Per. It is shown, that by means of the periodogram analysis, it is possible to determine the period of the main variability and to provide further detailed classification of semiregular pulsating stars, approximating their mean light curves with a trigonometric polynomial. It is offered to use the photometric period for estimates of physical parameters of pulsing stars.

  15. Luminosities of carbon-rich asymptotic giant branch stars in the Milky Way

    NASA Astrophysics Data System (ADS)

    Guandalini, R.; Cristallo, S.

    2013-07-01

    Context. Stars evolving along the asymptotic giant branch can become carbon-rich in the final part of their evolution. They replenish the inter-stellar medium with nuclear processed material via strong radiative stellar winds. The determination of the luminosity function of these stars, even if far from being conclusive, is extremely important for testing the reliability of theoretical models. In particular, strong constraints on the mixing treatment and the mass-loss rate can be derived. Aims: We present an updated luminosity function of Galactic carbon stars (LFGCS) obtained from a re-analysis of available data already published in previous papers. Methods: Starting from available near- and mid-infrared photometric data, we re-determined the selection criteria. Moreover, we took advantage of updated distance estimates and period-luminosity relations and we adopted a new formulation for the computation of bolometric corrections (BCs). This led us to collect an improved sample of carbon-rich sources from which we constructed an updated luminosity function. Results: The LFGCS peaks at magnitudes around -4.9, confirming the results obtained in a previous work. Nevertheless, the luminosity function presents two symmetrical tails instead of the larger high-luminosity tail characterizing the former luminosity function. Conclusions: The derived LFCGS matches the indications from recent theoretical evolutionary asymptotic giant branch models, thus confirming the validity of the choices of mixing treatment and mass-loss history. Moreover, we compare our new luminosity function with its counterpart in the Large Magellanic Cloud finding that the two distributions are very similar for dust-enshrouded sources, as expected from stellar evolutionary models. Finally, we derive a new fitting formula aimed to better determine BCs for C-stars. Table 1 is available in electronic form at http://www.aanda.org

  16. HV2112, a Thorne-Żytkow object or a super asymptotic giant branch star

    NASA Astrophysics Data System (ADS)

    Tout, Christopher A.; Żytkow, Anna N.; Church, Ross P.; Lau, Herbert H. B.; Doherty, Carolyn L.; Izzard, Robert G.

    2014-11-01

    The very bright red star HV2112 in the Small Magellanic Cloud could be a massive Thorne-Żytkow object (TŻO), a supergiant-like star with a degenerate neutron core. With a luminosity of over 105 L⊙, it could also be a super asymptotic giant branch (SAGB) star, a star with an oxygen/neon core supported by electron degeneracy and undergoing thermal pulses with third dredge up. Both TŻOs and SAGB stars are expected to be rare. Abundances of heavy elements in HV2112's atmosphere, as observed to date, do not allow us to distinguish between the two possibilities based on the latest models. Molybdenum and rubidium can be enhanced by both the irp-process in a TŻO or by the s-process in SAGB stars. Lithium can be generated by hot bottom burning at the base of the convective envelope in either. HV2112's enhanced calcium could thus be the key determinant. Neither SAGB stars nor TŻOs are known to be able to synthesize their own calcium but it may be possible to produce it in the final stages of the process that forms a TŻO, when the degenerate electron core of a giant star is tidally disrupted by a neutron star. Hence, it is more likely, on a fine balance, that HV2112 is indeed a genuine TŻO.

  17. Sodium abundances of AGB and RGB stars in Galactic globular clusters. I. Analysis and results of NGC 2808

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Primas, F.; Charbonnel, C.; Van der Swaelmen, M.; Bono, G.; Chantereau, W.; Zhao, G.

    2016-07-01

    Context. Galactic globular clusters (GC) are known to have multiple stellar populations and be characterised by similar chemical features, e.g. O-Na anti-correlation. While second-population stars, identified by their Na overabundance, have been found from the main sequence turn-off up to the tip of the red giant branch (RGB) in various Galactic GCs, asymptotic giant branch (AGB) stars have rarely been targeted. The recent finding that NGC 6752 lacks an Na-rich AGB star has thus triggered new studies on AGB stars in GCs, since this result questions our basic understanding of GC formation and stellar evolution theory. Aims: We aim to compare the Na abundance distributions of AGB and RGB stars in Galactic GCs and investigate whether the presence of Na-rich stars on the AGB is metallicity-dependent. Methods: With high-resolution spectra obtained with the multi-object high-resolution spectrograph FLAMES on ESO/VLT, we derived accurate Na abundances for 31 AGB and 40 RGB stars in the Galactic GC NGC 2808. Results: We find that NGC 2808 has a mean metallicity of -1.11 ± 0.08 dex, in good agreement with earlier analyses. Comparable Na abundance dispersions are derived for our AGB and RGB samples, with the AGB stars being slightly more concentrated than the RGB stars. The ratios of Na-poor first-population to Na-rich second-population stars are 45:55 in the AGB sample and 48:52 in the RGB sample. Conclusions: NGC 2808 has Na-rich second-population AGB stars, which turn out to be even more numerous - in relative terms - than their Na-poor AGB counterparts and the Na-rich stars on the RGB. Our findings are well reproduced by the fast rotating massive stars scenario and they do not contradict the recent results that there is not an Na-rich AGB star in NGC 6752. NGC 2808 thus joins the larger group of Galactic GCs for which Na-rich second-population stars on the AGB have recently been found. Based on observations made with ESO telescopes at the La Silla Paranal Observatory

  18. H I OBSERVATIONS OF THE ASYMPTOTIC GIANT BRANCH STAR X HERCULIS: DISCOVERY OF AN EXTENDED CIRCUMSTELLAR WAKE SUPERPOSED ON A COMPACT HIGH-VELOCITY CLOUD

    SciTech Connect

    Matthews, L. D.; Johnson, M. C.; Libert, Y.; Gerard, E.; Le Bertre, T.; Dame, T. M.

    2011-02-15

    We report H I 21 cm line observations of the asymptotic giant branch (AGB) star X Her obtained with the Robert C. Byrd Green Bank Telescope (GBT) and the Very Large Array. We have unambiguously detected H I emission associated with the circumstellar envelope of the star, with a mass totaling M{sub HI} {approx} 2.1 x 10{sup -3} M{sub sun}. The H I distribution exhibits a head-tail morphology, similar to those previously observed around the AGB stars Mira and RS Cnc. The tail is elongated along the direction of the star's space motion, with a total extent of {approx}> 6.'0 (0.24 pc) in the plane of the sky. We also detect a systematic radial velocity gradient of {approx}6.5 km s{sup -1} across the H I envelope. These results are consistent with the H I emission tracing a turbulent wake that arises from the motion of a mass-losing star through the interstellar medium (ISM). GBT mapping of a 2{sup 0} x 2{sup 0} region around X Her reveals that the star lies (in projection) near the periphery of a much larger H I cloud that also exhibits signatures of interaction with the ISM. The properties of the cloud are consistent with those of compact high-velocity clouds. Using {sup 12}CO J = 1-0 observations, we have placed an upper limit on its molecular gas content of N{sub H2} < 1.3 x 10{sup 20} cm{sup -2}. Although the distance to the cloud is poorly constrained, the probability of a chance coincidence in position, velocity, and apparent position angle of space motion between X Her and the cloud is extremely small, suggesting a possible physical association. However, the large H I mass of the cloud ({approx}>2.4 M{sub sun}) and the blueshift of its mean velocity relative to X Her are inconsistent with an origin tied directly to ejection from the star.

  19. Formation of SiC Grains in Pulsation-enhanced Dust-driven Wind around Carbon-rich Asymptotic Giant Branch Stars

    NASA Astrophysics Data System (ADS)

    Yasuda, Yuki; Kozasa, Takashi

    2012-02-01

    We investigate the formation of silicon carbide (SiC) grains in the framework of dust-driven wind around pulsating carbon-rich asymptotic giant branch (C-rich AGB) stars to reveal not only the amount but also the size distribution. Two cases are considered for the nucleation process: one is the local thermal equilibrium (LTE) case where the vibration temperature of SiC clusters T v is equal to the gas temperature as usual, and another is the non-LTE case in which T v is assumed to be the same as the temperature of small SiC grains. The results of the hydrodynamical calculations for a model with stellar parameters of mass M * = 1.0 M ⊙, luminosity L * = 104 L ⊙, effective temperature T eff = 2600 K, C/O ratio = 1.4, and pulsation period P = 650 days show the following: in the LTE case, SiC grains condense in accelerated outflowing gas after the formation of carbon grains, and the resulting averaged mass ratio of SiC to carbon grains of ~10-8 is too small to reproduce the value of 0.01-0.3, which is inferred from the radiative transfer models. On the other hand, in the non-LTE case, the formation region of the SiC grains is more internal and/or almost identical to that of the carbon grains due to the so-called inverse greenhouse effect. The mass ratio of SiC to carbon grains averaged at the outer boundary ranges from 0.098 to 0.23 for the sticking probability αs = 0.1-1.0. The size distributions with the peak at ~0.2-0.3 μm in radius cover the range of size derived from the analysis of the presolar SiC grains. Thus, the difference between the temperatures of the small cluster and gas plays a crucial role in the formation process of SiC grains around C-rich AGB stars, and this aspect should be explored for the formation process of dust grains in astrophysical environments.

  20. 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.

  1. 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.

  2. An asymptotic-giant-branch star in the progenitor system of a type Ia supernova.

    PubMed

    Hamuy, Mario; Phillips, M M; Suntzeff, Nicholas B; Maza, José; González, L E; Roth, Miguel; Krisciunas, Kevin; Morrell, Nidia; Green, E M; Persson, S E; McCarthy, P J

    2003-08-01

    Stars that explode as supernovae come in two main classes. A type Ia supernova is recognized by the absence of hydrogen and the presence of elements such as silicon and sulphur in its spectrum; this class of supernova is thought to produce the majority of iron-peak elements in the Universe. They are also used as precise 'standard candles' to measure the distances to galaxies. While there is general agreement that a type Ia supernova is produced by an exploding white dwarf star, no progenitor system has ever been directly observed. Significant effort has gone into searching for circumstellar material to help discriminate between the possible kinds of progenitor systems, but no such material has hitherto been found associated with a type Ia supernova. Here we report the presence of strong hydrogen emission associated with the type Ia supernova SN2002ic, indicating the presence of large amounts of circumstellar material. We infer from this that the progenitor system contained a massive asymptotic-giant-branch star that lost several solar masses of hydrogen-rich gas before the supernova explosion. PMID:12904786

  3. Highly Red Objects in M31: Candidates for Massive Young Stellar Objects or Superwind-Phase Asymptotic Giant Branch Stars

    NASA Astrophysics Data System (ADS)

    Kodaira, Keiichi; Tamura, Motohide; Vansevičius, Vladas; Miyazaki, Satoshi

    1998-06-01

    Several highly red objects (H-K>=0.9) are detected in the ~2'×2' field of OB association A24 near the 7 kpc spiral arm of M31. They show infrared excesses on the J-H versus H-K diagram, which is typical for stars with thick dust shells. We suspect them to be candidates either for compact young clusters containing massive young stellar objects or for superwind-phase asymptotic giant branch stars in M31.

  4. Evolution of oxygen-rich and carbon stars on the asymptotic giant branch

    NASA Technical Reports Server (NTRS)

    Kwok, Sun; Chan, S. Josephine; Volk, Kevine M.

    1989-01-01

    The transition from oxygen-rich (M) stars to S stars and then to C stars is examined using data on the chemical properties of the stars. The photospheric and circumstellar spectral characteristics of M and C stars are summarized. Consideration is given to the color distributions of carbon stars, visual carbon stars as transition objects, and radio observations of visual carbon stars. The chemical characteristics of S stars, the evolution of oxygen-rich stars on the AGB, and the transition between AGB stars and planetary nebulae are discussed. IRAS data are used to construct an evolutionary scenario for AGB stars, in which some mass-losing M stars remain oxygen rich, while others become carbon rich.

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

    NASA Technical Reports Server (NTRS)

    Stevens, Alyx Catherine; Sahai, Raghvendra

    2012-01-01

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

  6. 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.

  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. 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.

  9. The Effects of Rotation on s-process Nucleosynthesis in Asymptotic Giant Branch Stars

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

    In this paper, we analyze the effects induced by rotation on low-mass asymptotic giant branch stars. We compute two sets of models, M = 2.0 M ⊙ at [Fe/H] = 0 and M = 1.5 M ⊙ at [Fe/H] = -1.7, by adopting main-sequence rotation velocities in the range 0-120 km s-1. At high metallicity, we find that the Goldreich-Schubert-Fricke instability, active at the interface between the convective envelope and the rapid rotating core, contaminates the 13C-pocket (the major neutron source) with 14N (the major neutron poison), thus reducing the neutron flux available for the synthesis of heavy elements. As a consequence, the yields of heavy-s elements (Ba, La, Nd, Sm) and, to a lesser extent, those of light-s elements (Sr, Y, Zr) decrease with increasing rotation velocities up to 60 km s-1. However, for larger initial rotation velocities, the production of light-s and, to a lesser extent, that of heavy-s, begins again to increase, due to mixing induced by meridional circulations. At low metallicity, the effects of meridional circulations are important even at rather low rotation velocity. The combined effect of the Goldreich-Schubert-Fricke instability and meridional circulations determines an increase of light-s and, to a lesser extent, heavy-s elements, while lead is strongly reduced. For both metallicities, the rotation-induced instabilities active during the interpulse phase reduce the neutron-to-seed ratio, so that the spectroscopic indexes [hs/ls] and [Pb/hs] decrease by increasing the initial rotation velocity. Our analysis suggests that rotation could explain the spread in the s-process indexes, as observed in s-process enriched stars at different metallicities.

  10. Electron-capture supernovae of super-asymptotic giant branch stars and the Crab supernova 1054

    SciTech Connect

    Nomoto, Ken'ichi; Tominaga, Nozomu; Blinnikov, Sergei I.

    2014-05-02

    An electron-capture supernova (ECSN) is a core-collapse supernova explosion of a super-asymptotic giant branch (SAGB) star with a main-sequence mass M{sub Ms} ∼ 7 - 9.5M{sub ⊙}. The explosion takes place in accordance with core bounce and subsequent neutrino heating and is a unique example successfully produced by first-principle simulations. This allows us to derive a first self-consistent multicolor light curves of a core-collapse supernova. Adopting the explosion properties derived by the first-principle simulation, i.e., the low explosion energy of 1.5 × 10{sup 50} erg and the small {sup 56}Ni mass of 2.5 × 10{sup −3} M{sub ⊙}, we perform a multigroup radiation hydrodynamics calculation of ECSNe and present multicolor light curves of ECSNe of SAGB stars with various envelope mass and hydrogen abundance. We demonstrate that a shock breakout has peak luminosity of L ∼ 2 × 10{sup 44} erg s{sup −1} and can evaporate circumstellar dust up to R ∼ 10{sup 17} cm for a case of carbon dust, that plateau luminosity and plateau duration of ECSNe are L ∼ 10{sup 42} erg s{sup −1} and {sup t} ∼ 60 - 100 days, respectively, and that a plateau is followed by a tail with a luminosity drop by ∼ 4 mag. The ECSN shows a bright and short plateau that is as bright as typical Type II plateau supernovae, and a faint tail that might be influenced by spin-down luminosity of a newborn pulsar. Furthermore, the theoretical models are compared with ECSN candidates: SN 1054 and SN 2008S. We find that SN 1054 shares the characteristics of the ECSNe. For SN 2008S, we find that its faint plateau requires a ECSN model with a significantly low explosion energy of E ∼ 10{sup 48} erg.

  11. Electron-capture supernovae of super-asymptotic giant branch stars and the Crab supernova 1054

    NASA Astrophysics Data System (ADS)

    Nomoto, Ken'ichi; Tominaga, Nozomu; Blinnikov, Sergei I.

    2014-05-01

    An electron-capture supernova (ECSN) is a core-collapse supernova explosion of a super-asymptotic giant branch (SAGB) star with a main-sequence mass MMs ˜ 7 - 9.5M⊙. The explosion takes place in accordance with core bounce and subsequent neutrino heating and is a unique example successfully produced by first-principle simulations. This allows us to derive a first self-consistent multicolor light curves of a core-collapse supernova. Adopting the explosion properties derived by the first-principle simulation, i.e., the low explosion energy of 1.5 × 1050 erg and the small 56Ni mass of 2.5 × 10-3 M⊙, we perform a multigroup radiation hydrodynamics calculation of ECSNe and present multicolor light curves of ECSNe of SAGB stars with various envelope mass and hydrogen abundance. We demonstrate that a shock breakout has peak luminosity of L ˜ 2 × 1044 erg s-1 and can evaporate circumstellar dust up to R ˜ 1017 cm for a case of carbon dust, that plateau luminosity and plateau duration of ECSNe are L ˜ 1042 erg s-1 and t ˜ 60 - 100 days, respectively, and that a plateau is followed by a tail with a luminosity drop by ˜ 4 mag. The ECSN shows a bright and short plateau that is as bright as typical Type II plateau supernovae, and a faint tail that might be influenced by spin-down luminosity of a newborn pulsar. Furthermore, the theoretical models are compared with ECSN candidates: SN 1054 and SN 2008S. We find that SN 1054 shares the characteristics of the ECSNe. For SN 2008S, we find that its faint plateau requires a ECSN model with a significantly low explosion energy of E ˜ 1048 erg.

  12. THE EFFECTS OF ROTATION ON s-PROCESS NUCLEOSYNTHESIS IN ASYMPTOTIC GIANT BRANCH STARS

    SciTech Connect

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

    2013-09-10

    In this paper, we analyze the effects induced by rotation on low-mass asymptotic giant branch stars. We compute two sets of models, M = 2.0 M{sub Sun} at [Fe/H] = 0 and M = 1.5 M{sub Sun} at [Fe/H] = -1.7, by adopting main-sequence rotation velocities in the range 0-120 km s{sup -1}. At high metallicity, we find that the Goldreich-Schubert-Fricke instability, active at the interface between the convective envelope and the rapid rotating core, contaminates the {sup 13}C-pocket (the major neutron source) with {sup 14}N (the major neutron poison), thus reducing the neutron flux available for the synthesis of heavy elements. As a consequence, the yields of heavy-s elements (Ba, La, Nd, Sm) and, to a lesser extent, those of light-s elements (Sr, Y, Zr) decrease with increasing rotation velocities up to 60 km s{sup -1}. However, for larger initial rotation velocities, the production of light-s and, to a lesser extent, that of heavy-s, begins again to increase, due to mixing induced by meridional circulations. At low metallicity, the effects of meridional circulations are important even at rather low rotation velocity. The combined effect of the Goldreich-Schubert-Fricke instability and meridional circulations determines an increase of light-s and, to a lesser extent, heavy-s elements, while lead is strongly reduced. For both metallicities, the rotation-induced instabilities active during the interpulse phase reduce the neutron-to-seed ratio, so that the spectroscopic indexes [hs/ls] and [Pb/hs] decrease by increasing the initial rotation velocity. Our analysis suggests that rotation could explain the spread in the s-process indexes, as observed in s-process enriched stars at different metallicities.

  13. 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.

  14. Abundances of presolar graphite and SiC from supernovae and AGB stars in the Murchison meteorite

    SciTech Connect

    Amari, Sachiko; Zinner, Ernst; Gallino, Roberto

    2014-05-02

    Pesolar graphite grains exhibit a range of densities (1.65 – 2.20 g/cm{sup 3}). We investigated abundances of presolar graphite grains formed in supernovae and in asymptotic giant branch (AGB) stars in the four density fractions KE3, KFA1, KFB1 and KFC1 extracted from the Murchison meteorite to probe dust productions in these stellar sources. Seventy-six and 50% of the grains in the low-density fractions KE3 and KFA1, respectively, are supernova grains, while only 7.2% and 0.9% of the grains in the high-density fractions KFB1 and KFC1 have a supernova origin. Grains of AGB star origin are concentrated in the high-density fractions KFB1 and KFC1. From the C isotopic distributions of these fractions and the presence of s-process Kr with {sup 86}Kr/{sup 82}Kr = 4.43±0.46 in KFC1, we estimate that 76% and 80% of the grains in KFB1 and KFC1, respectively, formed in AGB stars. From the abundance of graphite grains in the Murchison meteorite, 0.88 ppm, the abundances of graphite from supernovae and AGB stars are 0.24 ppm and 0.44 ppm, respectively: the abundances of graphite in supernovae and AGB stars are comparable. In contrast, it has been known that 1% of SiC grains formed in supernovae and 95% formed in AGB stars in meteorites. Since the abundance of SiC grains is 5.85 ppm in the Murchison meteorite, the abundances of SiC from supernovae and AGB stars are 0.063 ppm and 5.6 ppm, respectively: the dominant source of SiC grains is AGB stars. Since SiC grains are harder and likely to survive better in space than graphite grains, the abundance of supernova graphite grains, which is higher than that of supernova SiC grains, indicates that supernovae proficiently produce graphite grains. Graphite grains from AGB stars are, in contrast, less abundant that SiC grains from AGB stars (0.44 ppm vs. 5.6 ppm). It is difficult to derive firm conclusions for graphite and SiC formation in AGB stars due to the difference in susceptibility to grain destruction. Metallicity of

  15. Abundances of presolar graphite and SiC from supernovae and AGB stars in the Murchison meteorite

    NASA Astrophysics Data System (ADS)

    Amari, Sachiko; Zinner, Ernst; Gallino, Roberto

    2014-05-01

    Pesolar graphite grains exhibit a range of densities (1.65 - 2.20 g/cm3). We investigated abundances of presolar graphite grains formed in supernovae and in asymptotic giant branch (AGB) stars in the four density fractions KE3, KFA1, KFB1 and KFC1 extracted from the Murchison meteorite to probe dust productions in these stellar sources. Seventy-six and 50% of the grains in the low-density fractions KE3 and KFA1, respectively, are supernova grains, while only 7.2% and 0.9% of the grains in the high-density fractions KFB1 and KFC1 have a supernova origin. Grains of AGB star origin are concentrated in the high-density fractions KFB1 and KFC1. From the C isotopic distributions of these fractions and the presence of s-process Kr with 86Kr/82Kr = 4.43±0.46 in KFC1, we estimate that 76% and 80% of the grains in KFB1 and KFC1, respectively, formed in AGB stars. From the abundance of graphite grains in the Murchison meteorite, 0.88 ppm, the abundances of graphite from supernovae and AGB stars are 0.24 ppm and 0.44 ppm, respectively: the abundances of graphite in supernovae and AGB stars are comparable. In contrast, it has been known that 1% of SiC grains formed in supernovae and 95% formed in AGB stars in meteorites. Since the abundance of SiC grains is 5.85 ppm in the Murchison meteorite, the abundances of SiC from supernovae and AGB stars are 0.063 ppm and 5.6 ppm, respectively: the dominant source of SiC grains is AGB stars. Since SiC grains are harder and likely to survive better in space than graphite grains, the abundance of supernova graphite grains, which is higher than that of supernova SiC grains, indicates that supernovae proficiently produce graphite grains. Graphite grains from AGB stars are, in contrast, less abundant that SiC grains from AGB stars (0.44 ppm vs. 5.6 ppm). It is difficult to derive firm conclusions for graphite and SiC formation in AGB stars due to the difference in susceptibility to grain destruction. Metallicity of the parent AGB stars of

  16. Ground-based infrared observations of variable IRAS sources as candidates for late asymptotic giant branch stars

    NASA Technical Reports Server (NTRS)

    Kwok, Sun; Boreiko, R. T.; Hrivnak, Bruce J.

    1987-01-01

    Analysis of the color distribution of OH/IR stars and IRAS low-resolution spectra class 30 objects suggests the presence of a well-defined evolutionary sequence which is populated by late asymptotic giant branch (LAGB) stars. The paper reports ground-based identification and infrared photometry of 10 candidates of news LAGB stars. None of the selected sources are found to have optical counterparts, and eight of the 10 show a strong 10-micron silicate absorption feature. It is suggested that these stars represent an invisible extension of extreme Mira variables and are some of the most evolved stars observed to date.

  17. The Contribution of TP-AGB Stars to the Mid-infrared Colors of Nearby Galaxies

    NASA Astrophysics Data System (ADS)

    Chisari, Nora E.; Kelson, Daniel D.

    2012-07-01

    We study the mid-infrared color space of 30 galaxies from the Spitzer Infrared Nearby Galaxies Survey (SINGS) survey for which Sloan Digital Sky Survey data are also available. We construct two-color maps for each galaxy and compare them to results obtained from combining Maraston evolutionary synthesis models, galactic thermally pulsating asymptotic giant branch (TP-AGB) colors, and smooth star formation histories. For most of the SINGS sample, the spatially extended mid-IR emission seen by Spitzer in normal galaxies is consistent with our simple model in which circumstellar dust from TP-AGB stars dominates at 8 and 24 μm. There is a handful of exceptions that we identify as galaxies that have high star formation rates presumably with star formation histories that cannot be assumed to be smooth, or anemic galaxies, which were depleted of their H I at some point during their evolution and have very low ongoing star formation rates.

  18. A chemically peculiar post-AGB star in the Small Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Kamath, D.; Van Winckel, H.; De Smedt, K.; Wood, P. R.

    2016-07-01

    Post-Asymptotic Giant Branch (post-AGB) stars bear signatures of the entire chemical and morphological changes that occur prior to and during the AGB phase of evolution. These objects also provide vital clues on the ultimate fate of the star. Detailed chemical abundance studies of some of these objects have shown that they are chemically much more diverse than anticipated. As expected, some are the most s-process enriched objects known to date while others are not s-process enriched. Our recent study has revealed a star in the Small Magellanic Cloud, J005252.87-722842.9, which displays a peculiar chemical signature that does not correspond to the expected chemical diversity observed in these objects. This unique object reveals the possibility of a new stellar evolutionary channel where the star evolves without any third dredge-up episodes or during its evolution becomes devoid of its nucleosynthetic history.

  19. THE CONTRIBUTION OF TP-AGB STARS TO THE MID-INFRARED COLORS OF NEARBY GALAXIES

    SciTech Connect

    Chisari, Nora E.; Kelson, Daniel D.

    2012-07-10

    We study the mid-infrared color space of 30 galaxies from the Spitzer Infrared Nearby Galaxies Survey (SINGS) survey for which Sloan Digital Sky Survey data are also available. We construct two-color maps for each galaxy and compare them to results obtained from combining Maraston evolutionary synthesis models, galactic thermally pulsating asymptotic giant branch (TP-AGB) colors, and smooth star formation histories. For most of the SINGS sample, the spatially extended mid-IR emission seen by Spitzer in normal galaxies is consistent with our simple model in which circumstellar dust from TP-AGB stars dominates at 8 and 24 {mu}m. There is a handful of exceptions that we identify as galaxies that have high star formation rates presumably with star formation histories that cannot be assumed to be smooth, or anemic galaxies, which were depleted of their H I at some point during their evolution and have very low ongoing star formation rates.

  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. Lithium-rich Giants in Globular Clusters

    NASA Astrophysics Data System (ADS)

    Kirby, Evan N.; Guhathakurta, Puragra; Zhang, Andrew J.; Hong, Jerry; Guo, Michelle; Guo, Rachel; Cohen, Judith G.; Cunha, Katia

    2016-03-01

    Although red giants deplete lithium on their surfaces, some giants are Li-rich. Intermediate-mass asymptotic giant branch (AGB) stars can generate Li through the Cameron-Fowler conveyor, but the existence of Li-rich, low-mass red giant branch (RGB) stars is puzzling. Globular clusters are the best sites to examine this phenomenon because it is straightforward to determine membership in the cluster and to identify the evolutionary state of each star. In 72 hours of Keck/DEIMOS exposures in 25 clusters, we found four Li-rich RGB and two Li-rich AGB stars. There were 1696 RGB and 125 AGB stars with measurements or upper limits consistent with normal abundances of Li. Hence, the frequency of Li-richness in globular clusters is (0.2 ± 0.1)% for the RGB, (1.6 ± 1.1)% for the AGB, and (0.3 ± 0.1)% for all giants. Because the Li-rich RGB stars are on the lower RGB, Li self-generation mechanisms proposed to occur at the luminosity function bump or He core flash cannot explain these four lower RGB stars. We propose the following origin for Li enrichment: (1) All luminous giants experience a brief phase of Li enrichment at the He core flash. (2) All post-RGB stars with binary companions on the lower RGB will engage in mass transfer. This scenario predicts that 0.1% of lower RGB stars will appear Li-rich due to mass transfer from a recently Li-enhanced companion. This frequency is at the lower end of our confidence interval. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

  2. Hubble Space Telescope/NICMOS Observations of I Zw 18: A Population of Old Asymptotic Giant Branch Stars Revealed.

    PubMed

    Östlin

    2000-06-01

    I present the first results from a Hubble Space Telescope/NICMOS imaging study of the most metal-poor blue compact dwarf galaxy, I Zw 18. The near-infrared color-magnitude diagram (CMD) is dominated by two populations, one 10-20 Myr population of red supergiants and one 0.1-5 Gyr population of asymptotic giant branch stars. Stars older than 1 Gyr are required to explain the observed CMD at the adopted distance of 12.6 Mpc, showing that I Zw 18 is not a young galaxy. The results hold also if the distance to I Zw 18 is significantly larger. This rules out the possibility that I Zw 18 is a truly young galaxy formed recently in the local universe. PMID:10835308

  3. 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

  4. Condensation of refractory metals in asymptotic giant branch and other stellar environments

    SciTech Connect

    Schwander, D.; Berg, T.; Schönhense, G.; Ott, U.

    2014-09-20

    The condensation of material from a gas of solar composition has been extensively studied, but less so condensation in the environment of evolved stars, which has been mainly restricted to major compounds and some specific element groups such as the Rare Earth elements. Also of interest, however, are refractory metals like Mo, Ru, Os, W, Ir, and Pt, which may condense to form refractory metal nuggets (RMNs) like the ones that have been found in association with presolar graphite. We have performed calculations describing the condensation of these elements in the outflows of s-process enriched AGB stars as well as from gas enriched in r-process products. While in carbon-rich environments (C > O), the formation of carbides is expected to consume W, Mo, and V (Lodders and Fegley), the condensation sequence for the other refractory metals under these conditions does not significantly differ from the case of a cooling gas of solar composition. The composition in detail, however, is significantly different due to the completely different source composition. Condensation from an r-process enriched source differs less from the solar case. Elemental abundance ratios of the refractory metals can serve as a guide for finding candidate presolar grains among the RMNs in primitive meteorites—most of which have a solar system origin—for confirmation by isotopic analysis. We apply our calculations to the case of the four RMNs found by Croat et al., which may very well be presolar.

  5. Relics of Ancient Post-AGB Stars in a Primitive Meteorite

    NASA Astrophysics Data System (ADS)

    Jadhav, M.; Pignatari, M.; Herwig, F.; Zinner, E.; Gallino, R.; Huss, G. R.

    2013-11-01

    Graphite is one of the many presolar circumstellar condensate species found in primitive meteorites. While the isotopic compositions of low-density graphite grains indicate an origin in core-collapse supernovae, some high-density grains have extreme isotopic anomalies in C, Ca, and Ti, which cannot be explained by envelope predictions of asymptotic giant branch (AGB) stars or theoretical supernova models. The Ca and Ti isotopic anomalies, however, match the predictions of He-shell abundances in AGB stars. In this study, we show that the C, Ca, and Ti isotopic anomalies are consistent with nucleosynthesis predictions of the H-ingestion phase during a very late thermal pulse (VLTP) event in post-AGB stars. The low 12C/13C isotopic ratios in these grains are a result of abundant 12C efficiently capturing the protons that are being ingested during the VLTP. Very high neutron densities of ~1015 cm-3, typical of the i-process, are achieved during this phase in post-AGB stars. The large 42, 43, 44Ca excesses in some graphite grains are indicative of neutron capture nucleosynthesis during VLTP. The comparison of VLTP nucleosynthesis calculations to the graphite data also indicate that apparent anomalies in the Ti isotopic ratios are due to large contributions from 46, 48Ca, which cannot be resolved from the isobars 46, 48Ti during the measurements. We conclude that presolar graphite grains with moderate to extreme Ca and Ti isotopic anomalies originate in post-AGB stars that suffer a VLTP.

  6. RELICS OF ANCIENT POST-AGB STARS IN A PRIMITIVE METEORITE

    SciTech Connect

    Jadhav, M.; Huss, G. R.; Pignatari, M.; Herwig, F.; Zinner, E.; Gallino, R.

    2013-11-10

    Graphite is one of the many presolar circumstellar condensate species found in primitive meteorites. While the isotopic compositions of low-density graphite grains indicate an origin in core-collapse supernovae, some high-density grains have extreme isotopic anomalies in C, Ca, and Ti, which cannot be explained by envelope predictions of asymptotic giant branch (AGB) stars or theoretical supernova models. The Ca and Ti isotopic anomalies, however, match the predictions of He-shell abundances in AGB stars. In this study, we show that the C, Ca, and Ti isotopic anomalies are consistent with nucleosynthesis predictions of the H-ingestion phase during a very late thermal pulse (VLTP) event in post-AGB stars. The low {sup 12}C/{sup 13}C isotopic ratios in these grains are a result of abundant {sup 12}C efficiently capturing the protons that are being ingested during the VLTP. Very high neutron densities of ∼10{sup 15} cm{sup –3}, typical of the i-process, are achieved during this phase in post-AGB stars. The large {sup 42,43,44}Ca excesses in some graphite grains are indicative of neutron capture nucleosynthesis during VLTP. The comparison of VLTP nucleosynthesis calculations to the graphite data also indicate that apparent anomalies in the Ti isotopic ratios are due to large contributions from {sup 46,48}Ca, which cannot be resolved from the isobars {sup 46,48}Ti during the measurements. We conclude that presolar graphite grains with moderate to extreme Ca and Ti isotopic anomalies originate in post-AGB stars that suffer a VLTP.

  7. Photodissociation and chemistry of N2 in the circumstellar envelope of carbon-rich AGB stars

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

    Context. The envelopes of asymptotic giant branch (AGB) stars are irradiated externally by ultraviolet photons; hence, the chemistry is sensitive to the photodissociation of N2 and CO, which are major reservoirs of nitrogen and carbon, respectively. The photodissociation of N2 has recently been quantified by laboratory and theoretical studies. Improvements have also been made for CO photodissociation. Aims: For the first time, we use accurate N2 and CO photodissociation rates and shielding functions in a model of the circumstellar envelope of the carbon-rich AGB star, IRC +10216. Methods: We use a state-of-the-art chemical model of an AGB envelope, the latest CO and N2 photodissociation data, and a new method for implementing molecular shielding functions in full spherical geometry with isotropic incident radiation. We compare computed column densities and radial distributions of molecules with observations. Results: The transition of N2→ N (also, CO → C → C+) is shifted towards the outer envelope relative to previous models. This leads to different column densities and radial distributions of N-bearing species, especially those species whose formation/destruction processes largely depend on the availability of atomic or molecular nitrogen, for example, CnN (n = 1, 3, 5), CnN- (n = 1, 3, 5), HCnN (n = 1, 3, 5, 7, 9), H2CN and CH2CN. Conclusions: The chemistry of many species is directly or indirectly affected by the photodissociation of N2 and CO, especially in the outer shell of AGB stars where photodissociation is important. Thus, it is important to include N2 and CO shielding in astrochemical models of AGB envelopes and other irradiated environments. In general, while differences remain between our model of IRC +10216 and the observed molecular column densities, better agreement is found between the calculated and observed radii of peak abundance.

  8. On the introduction of {sup 17}O+p reaction rates evaluated through the THM in AGB nucleosynthesis calculations

    SciTech Connect

    Palmerini, S.; Sergi, M. L.; La Cognata, M.; Pizzone, R. G.; Lamia, L.; Spitaleri, C.

    2014-05-09

    The rates for the {sup 17}O(p,αα{sup 14}N, {sup 17}O(p,α){sup 18}F and {sup 18}O(p,α){sup 15}N reactions deduced trough the Trojan Horse Method (THM) have been introduced into a state-of-the-art asymptotic giant branch (AGB) models for proton-capture nucleosynthesis and cool bottom process. The predicted abundances have been compared with isotopic compositions provided by geochemical analysis of presolar grains. As a result, an improved agreement is found between the models and the isotopic mix of oxide grains of AGB origins, whose composition is the signature of low-temperature proton-capture nucleosynthesis.

  9. 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.

  10. SMA Spectral Line Imaging Survey at 279 - 355 GHz of the Oxygen-rich AGB Star IK Tau

    NASA Astrophysics Data System (ADS)

    De Beck, E.; Kamiński, T.; Menten, K. M.; Patel, N. A.; Young, K. H.; Gottlieb, C. A.

    2015-08-01

    Dedicated, unbiased spectral scans of asymptotic giant branch stars have so far been published only for a few carbon-rich stars, with a strong focus on the nearby and bright IRC +10216. We present results from a spectral survey of the circumstellar envelope of the oxygen-rich AGB star IK Tau obtained with the Submillimeter Array (SMA) at ~ 0'.9 angular resolution in the frequency range 279-355 GHz, expanding the molecular inventory for M-type evolved stars and filling an observational gap. The survey shows over 140 emission lines, belonging to more than 30 species. The emission of AlO and of several vibrationally excited species traces the acceleration of the wind. Isotopic ratios for carbon, silicon, and sulfur will be derived from the observed emission of isotopologues of CO, SiO, SiS, HCN, SO, and SO2. This will allow us to constrain the AGB nucleosynthesis of IK Tau. We highlight the first detection of PO and PN around an oxygen-rich AGB star, detected at unexpectedly high abundances, and emphasise the importance of unbiased spectral surveys of AGB stars and the need for updated chemical models.

  11. 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.

  12. Testing the effect of continuum elimination methods on studies of infrared dust features from AGB star spectra

    NASA Astrophysics Data System (ADS)

    Delisle, Colby; Speck, A.

    2014-01-01

    Asymptotic Giant Branch (AGB) stars are major contributors of cosmic dust to the interstellar medium. Understanding the cosmic dust ejected from these stars is essential to understanding the broader topics of evolution and composition of stellar and interstellar objects in our universe. AGB stars produce either carbon- or oxygen (O)-rich dust. O-rich AGB stars have been classified into groups according to the shapes of their spectral features in the mid-infrared (IR). Because their spectral features are similar, stars within each group are expected to have similar dust shell parameters, especially with respect to the composition of the dust. We have selected a sample of 26 O-rich AGB stars, in a single group in order to investigate an apparently homogenous group of stars. In particular, we chose stars in group SE1. Using spectral data from the Infrared Space Observatory (ISO), and the Infrared Astronomical Satellite (IRAS) we investigated variations in the spectral parameters of these stars: i.e. continuum temperature, feature strength, peak position(s), FWHM. In this preliminary work we present a study of the effect of the methods by which we eliminate the continuum prior to measuring the feature parameters.

  13. 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

  14. THE SPECTRAL ENERGY DISTRIBUTION OF POST-STARBURST GALAXIES IN THE NEWFIRM MEDIUM-BAND SURVEY: A LOW CONTRIBUTION FROM TP-AGB STARS

    SciTech Connect

    Kriek, Mariska; Conroy, Charlie; Labbe, Ivo; Whitaker, Katherine E.; Van Dokkum, Pieter G.; Brammer, Gabriel B.; Muzzin, Adam; Franx, Marijn; Quadri, Ryan F.; Illingworth, Garth D.; Rudnick, Gregory

    2010-10-10

    Stellar population synthesis (SPS) models are a key ingredient of many galaxy evolution studies. Unfortunately, the models are still poorly calibrated for certain stellar evolution stages. Of particular concern is the treatment of the thermally pulsing asymptotic giant branch (TP-AGB) phase, as different implementations lead to systematic differences in derived galaxy properties. Post-starburst galaxies are a promising calibration sample, as TP-AGB stars are thought to be most prominently visible during this phase. Here, we use post-starburst galaxies in the NEWFIRM medium-band survey to assess different SPS models. The available photometry allows the selection of a homogeneous and well-defined sample of 62 post-starburst galaxies at 0.7 {approx_lt} z {approx_lt} 2.0, from which we construct a well-sampled composite spectral energy distribution (SED) over the range 1200-40000 A. The SED is well fit by the Bruzual and Charlot SPS models, while the Maraston models do not reproduce the rest-frame optical and near-infrared parts of the SED simultaneously. When the fitting is restricted to {lambda} < 6000 A, the Maraston models overpredict the near-infrared luminosity, implying that these models give too much weight to TP-AGB stars. Using the flexible SPS models by Conroy et al. and assuming solar metallicity, we find that the contribution of TP-AGB stars to the integrated SED is a factor of {approx}3 lower than predicted by the latest Padova TP-AGB models. Whether this is due to lower bolometric luminosities, shorter lifetimes, and/or heavy dust obscuration of TP-AGB stars remains to be addressed. Altogether, our data demand a low contribution from TP-AGB stars to the SED of post-starburst galaxies.

  15. 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.

  16. 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.

  17. 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.

  18. The Frequency of Lithium-Rich Giants in Globular Clusters

    NASA Astrophysics Data System (ADS)

    Kirby, Evan N.; Guhathakurta, Puragra; Zhang, Andrew J.; Hong, Jerry; Guo, Michelle; Guo, Rachel; Cohen, Judith G.; Cunha, Katia M. L.

    2016-01-01

    Although red giants destroy lithium, some giants are Li-rich. Intermediate-mass asymptotic giant branch (AGB) stars can generate Li through the Cameron-Fowler conveyor, but the existence of Li-rich, low-mass red giant branch (RGB) stars is puzzling. Globular clusters are the best sites to examine this phenomenon because it is straightforward to determine membership in the cluster and to identify the evolutionary state of each star. In 72 hours of Keck/DEIMOS exposures in 25 clusters, we found four Li-rich RGB and two Li-rich AGB stars. There were 1696 RGB and 125 AGB stars with measurements or upper limits consistent with normal abundances of Li. Hence, the frequency of Li-richness in globular clusters is (0.2 ± 0.1)% for the RGB, (1.6 ± 1.1)% for the AGB, and (0.3 ± 0.1)% for all giants. Because the Li-rich RGB stars are on the lower RGB, Li self-generation mechanisms proposed to occur at the luminosity function bump or He core flash cannot explain these four lower RGB stars. We propose the following origin for Li enrichment: (1) All luminous giants experience a brief phase of Li enrichment at the He core flash. (2) All post-RGB stars with binary companions on the lower RGB will engage in mass transfer. This scenario predicts that 0.1% of lower RGB stars will appear Li-rich due to mass transfer from a recently Li-enhanced companion. This frequency is at the lower end of our confidence interval.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Carbon-rich dust past the asymptotic giant branch: Aliphatics, aromatics, and fullerenes in the Magellanic Clouds

    SciTech Connect

    Sloan, G. C.; Lagadec, E.; Zijlstra, A. A.; Kraemer, K. E.; Weis, A. P.; Matsuura, M.; Volk, K.; Peeters, E.; Cami, J.; Duley, W. W.; Bernard-Salas, J.; Kemper, F.

    2014-08-10

    Infrared spectra of carbon-rich objects that have evolved off the asymptotic giant branch reveal a range of dust properties, including fullerenes, polycyclic aromatic hydrocarbons (PAHs), aliphatic hydrocarbons, and several unidentified features, including the 21 μm emission feature. To test for the presence of fullerenes, we used the position and width of the feature at 18.7-18.9 μm and examined other features at 17.4 and 6-9 μm. This method adds three new fullerene sources to the known sample, but it also calls into question three previous identifications. We confirm that the strong 11 μm features seen in some sources arise primarily from SiC, which may exist as a coating around carbonaceous cores and result from photo-processing. Spectra showing the 21 μm feature usually show the newly defined Class D PAH profile at 7-9 μm. These spectra exhibit unusual PAH profiles at 11-14 μm, with weak contributions at 12.7 μm, which we define as Class D1, or show features shifted to ∼11.4, 12.4, and 13.2 μm, which we define as Class D2. Alkyne hydrocarbons match the 15.8 μm feature associated with 21 μm emission. Sources showing fullerene emission but no PAHs have blue colors in the optical, suggesting a clear line of sight to the central source. Spectra with 21 μm features and Class D2 PAH emission also show photometric evidence for a relatively clear line of sight to the central source. The multiple associations of the 21 μm feature with aliphatic hydrocarbons suggest that the carrier is related to this material in some way.

  7. On the metallicity dependence of crystalline silicates in oxygen-rich asymptotic giant branch stars and red supergiants

    NASA Astrophysics Data System (ADS)

    Jones, O. C.; Kemper, F.; Sargent, B. A.; McDonald, I.; Gielen, C.; Woods, Paul M.; Sloan, G. C.; Boyer, M. L.; Zijlstra, A. A.; Clayton, G. C.; Kraemer, K. E.; Srinivasan, S.; Ruffle, P. M. E.

    2012-12-01

    We investigate the occurrence of crystalline silicates in oxygen-rich evolved stars across a range of metallicities and mass-loss rates. It has been suggested that the crystalline silicate feature strength increases with increasing mass-loss rate, implying a correlation between lattice structure and wind density. To test this, we analyse Spitzer Infrared Spectrograph and Infrared Space Observatory Short Wavelength Spectrometer spectra of 217 oxygen-rich asymptotic giant branch and 98 red supergiants in the Milky Way, the Large and Small Magellanic Clouds, and Galactic globular clusters. These encompass a range of spectral morphologies from the spectrally rich which exhibit a wealth of crystalline and amorphous silicate features to 'naked' (dust-free) stars. We combine spectroscopic and photometric observations with the GRAMS grid of radiative transfer models to derive (dust) mass-loss rates and temperature. We then measure the strength of the crystalline silicate bands at 23, 28 and 33 μm. We detect crystalline silicates in stars with dust mass-loss rates which span over 3 dex, down to rates of ˜10-9 M⊙ yr-1. Detections of crystalline silicates are more prevalent in higher mass-loss rate objects, though the highest mass-loss rate objects do not show the 23-μm feature, possibly due to the low temperature of the forsterite grains or it may indicate that the 23-μm band is going into absorption due to high column density. Furthermore, we detect a change in the crystalline silicate mineralogy with metallicity, with enstatite seen increasingly at low metallicity.

  8. Carbon-rich Dust Past the Asymptotic Giant Branch: Aliphatics, Aromatics, and Fullerenes in the Magellanic Clouds

    NASA Astrophysics Data System (ADS)

    Sloan, G. C.; Lagadec, E.; Zijlstra, A. A.; Kraemer, K. E.; Weis, A. P.; Matsuura, M.; Volk, K.; Peeters, E.; Duley, W. W.; Cami, J.; Bernard-Salas, J.; Kemper, F.; Sahai, R.

    2014-08-01

    Infrared spectra of carbon-rich objects that have evolved off the asymptotic giant branch reveal a range of dust properties, including fullerenes, polycyclic aromatic hydrocarbons (PAHs), aliphatic hydrocarbons, and several unidentified features, including the 21 μm emission feature. To test for the presence of fullerenes, we used the position and width of the feature at 18.7-18.9 μm and examined other features at 17.4 and 6-9 μm. This method adds three new fullerene sources to the known sample, but it also calls into question three previous identifications. We confirm that the strong 11 μm features seen in some sources arise primarily from SiC, which may exist as a coating around carbonaceous cores and result from photo-processing. Spectra showing the 21 μm feature usually show the newly defined Class D PAH profile at 7-9 μm. These spectra exhibit unusual PAH profiles at 11-14 μm, with weak contributions at 12.7 μm, which we define as Class D1, or show features shifted to ~11.4, 12.4, and 13.2 μm, which we define as Class D2. Alkyne hydrocarbons match the 15.8 μm feature associated with 21 μm emission. Sources showing fullerene emission but no PAHs have blue colors in the optical, suggesting a clear line of sight to the central source. Spectra with 21 μm features and Class D2 PAH emission also show photometric evidence for a relatively clear line of sight to the central source. The multiple associations of the 21 μm feature with aliphatic hydrocarbons suggest that the carrier is related to this material in some way.

  9. Supernova Explosions of Super-asymptotic Giant Branch Stars: Multicolor Light Curves of Electron-capture Supernovae

    NASA Astrophysics Data System (ADS)

    Tominaga, Nozomu; Blinnikov, Sergei I.; Nomoto, Ken'ichi

    2013-07-01

    An electron-capture supernova (ECSN) is a core-collapse supernova (CCSN) explosion of a super-asymptotic giant branch (SAGB) star with a main-sequence mass M MS ~ 7-9.5 M ⊙. The explosion takes place in accordance with core bounce and subsequent neutrino heating and is a unique example successfully produced by first-principle simulations. This allows us to derive a first self-consistent multicolor light curve of a CCSN. Adopting the explosion properties derived by the first-principle simulation, i.e., the low explosion energy of 1.5 × 1050 erg and the small 56Ni mass of 2.5 × 10-3 M ⊙, we perform a multi-group radiation hydrodynamics calculation of ECSNe and present multicolor light curves of ECSNe of SAGB stars with various envelope masses and hydrogen abundances. We demonstrate that a shock breakout has a peak luminosity of L ~ 2 × 1044 erg s-1 and can evaporate circumstellar dust up to R ~ 1017 cm for the case of carbon dust, that the plateau luminosity and plateau duration of ECSNe are L ~ 1042 erg s-1 and t ~ 60-100 days, respectively, and that a plateau is followed by a tail with a luminosity drop by ~4 mag. The ECSN shows a bright and short plateau that is as bright as typical Type II plateau supernovae, and a faint tail that might be influenced by the spin-down luminosity of a newborn pulsar. Furthermore, the theoretical models are compared with ECSN candidates: SN 1054 and SN 2008S. We find that SN 1054 shares the characteristics of the ECSNe. For SN 2008S, we find that its faint plateau requires an ECSN model with a significantly low explosion energy of E ~ 1048 erg.

  10. 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.

  11. The {sup 13}C-pocket structure in AGB models: constraints from zirconium isotope abundances in single mainstream SiC grains

    SciTech Connect

    Liu, Nan; Davis, Andrew M.; Pellin, Michael J.; Gallino, Roberto; Bisterzo, Sara; Savina, Michael R.

    2014-06-20

    We present postprocess asymptotic giant branch (AGB) nucleosynthesis models with different {sup 13}C-pocket internal structures to better explain zirconium isotope measurements in mainstream presolar SiC grains by Nicolussi et al. and Barzyk et al. We show that higher-than-solar {sup 92}Zr/{sup 94}Zr ratios can be predicted by adopting a {sup 13}C-pocket with a flat {sup 13}C profile, instead of the previous decreasing-with-depth {sup 13}C profile. The improved agreement between grain data for zirconium isotopes and AGB models provides additional support for a recent proposal of a flat {sup 13}C profile based on barium isotopes in mainstream SiC grains by Liu et al.

  12. The AGB star nucleosynthesis in the light of the recent 17O ( p ,α)14N and 18O ( p ,α)15N reaction rate determinations

    NASA Astrophysics Data System (ADS)

    Palmerini, S.; Sergi, M. L.; La Cognata, M.; Lamia, L.; Pizzone, R. G.; Spitaleri, C.

    2015-02-01

    Presolar grains form in the cold and dusty envelopes of Asymptotic Giant Branch (AGB) stars. These solides, once that have been ejected by stellar winds, come to us as inclusions in meteorites providing invaluable benchmarks and constraints for our knowledge of low temeperature H-burning in stars. The Trojan Horse Method (THM) has been used to investigate the low-energy cross sections of the 17O ( p ,α)14N and 18O ( p ,α)15N reactions. Moreover, the strength of the 65 keV resonance in the 17O ( p ,α)14N reaction, measured by means of the THM, has been used to renormalize the corresponding resonance strength in the 17O + p radiative capture channel. The new estimates of the reaction rates have been introduced into calculations of AGB star nucleosynthesis and the results have been compared with geochemical analysis of "presolar" grains to determine their impact on astrophysical environments.

  13. The 13C-Pocket Structure in AGB Models: Constraints from Zirconium Isotope Abundances in Single Mainstream SiC Grains

    NASA Astrophysics Data System (ADS)

    Liu, Nan; Gallino, Roberto; Bisterzo, Sara; Davis, Andrew M.; Savina, Michael R.; Pellin, Michael J.

    2014-06-01

    We present postprocess asymptotic giant branch (AGB) nucleosynthesis models with different 13C-pocket internal structures to better explain zirconium isotope measurements in mainstream presolar SiC grains by Nicolussi et al. and Barzyk et al. We show that higher-than-solar 92Zr/94Zr ratios can be predicted by adopting a 13C-pocket with a flat 13C profile, instead of the previous decreasing-with-depth 13C profile. The improved agreement between grain data for zirconium isotopes and AGB models provides additional support for a recent proposal of a flat 13C profile based on barium isotopes in mainstream SiC grains by Liu et al.

  14. AN INFRARED CENSUS OF DUST IN NEARBY GALAXIES WITH SPITZER (DUSTiNGS). II. DISCOVERY OF METAL-POOR DUSTY AGB STARS

    SciTech Connect

    Boyer, Martha L.; Sonneborn, George; McQuinn, Kristen B. W.; Gehrz, Robert D.; Skillman, Evan; Barmby, Pauline; Bonanos, Alceste Z.; Gordon, Karl D.; Meixner, Margaret; Groenewegen, M. A. T.; Lagadec, Eric; Lennon, Daniel; Marengo, Massimo; McDonald, Iain; Zijlstra, Albert; Sloan, G. C.; Van Loon, Jacco Th.

    2015-02-10

    The DUSTiNGS survey (DUST in Nearby Galaxies with Spitzer) is a 3.6 and 4.5 μm imaging survey of 50 nearby dwarf galaxies designed to identify dust-producing asymptotic giant branch (AGB) stars and massive stars. Using two epochs, spaced approximately six months apart, we identify a total of 526 dusty variable AGB stars (sometimes called ''extreme'' or x-AGB stars; [3.6]-[4.5] > 0.1 mag). Of these, 111 are in galaxies with [Fe/H] < –1.5 and 12 are in galaxies with [Fe/H] < –2.0, making them the most metal-poor dust-producing AGB stars known. We compare these identifications to those in the literature and find that most are newly discovered large-amplitude variables, with the exception of ≈30 stars in NGC 185 and NGC 147, 1 star in IC 1613, and 1 star in Phoenix. The chemical abundances of the x-AGB variables are unknown, but the low metallicities suggest that they are more likely to be carbon-rich than oxygen-rich and comparisons with existing optical and near-IR photometry confirm that 70 of the x-AGB variables are confirmed or likely carbon stars. We see an increase in the pulsation amplitude with increased dust production, supporting previous studies suggesting that dust production and pulsation are linked. We find no strong evidence linking dust production with metallicity, indicating that dust can form in very metal-poor environments.

  15. 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.

  16. Astrophysical Reaction Rate for the Neutron-Generator Reaction {sup 13}C({alpha},n){sup 16}O in Asymptotic Giant Branch Stars

    SciTech Connect

    Johnson, E. D.; Rogachev, G. V.; Baby, L. T.; Cluff, W. T.; Crisp, A. M.; Diffenderfer, E.; Green, B. W.; Hinners, T.; Hoffman, C. R.; Kemper, K. W.; Momotyuk, O.; Peplowski, P.; Pipidis, A.; Reynolds, R.; Roeder, B. T.; Mukhamedzhanov, A. M.; Goldberg, V. Z.; Brown, S.

    2006-11-10

    The reaction {sup 13}C({alpha},n) is considered to be the main source of neutrons for the s process in asymptotic giant branch stars. At low energies, the cross section is dominated by the 1/2{sup +} 6.356 MeV subthreshold resonance in {sup 17}O whose contribution at stellar temperatures is uncertain by a factor of 10. In this work, we performed the most precise determination of the low-energy astrophysical S factor using the indirect asymptotic normalization (ANC) technique. The {alpha}-particle ANC for the subthreshold state has been measured using the sub-Coulomb {alpha}-transfer reaction ({sup 6}Li,d). Using the determined ANC, we calculated S(0), which turns out to be an order of magnitude smaller than in the nuclear astrophysics compilation of reaction rates.

  17. 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.

  18. Spitzer SAGE-Spec: Near infrared spectroscopy, dust shells, and cool envelopes in extreme Large Magellanic Cloud asymptotic giant branch stars

    SciTech Connect

    Blum, R. D.; Srinivasan, S.; Kemper, F.; Ling, B.

    2014-11-01

    K-band spectra are presented for a sample of 39 Spitzer Infrared Spectrograph (IRS) SAGE-Spec sources in the Large Magellanic Cloud. The spectra exhibit characteristics in very good agreement with their positions in the near-infrared—Spitzer color-magnitude diagrams and their properties as deduced from the Spitzer IRS spectra. Specifically, the near-infrared spectra show strong atomic and molecular features representative of oxygen-rich and carbon-rich asymptotic giant branch stars, respectively. A small subset of stars was chosen from the luminous and red extreme ''tip'' of the color-magnitude diagram. These objects have properties consistent with dusty envelopes but also cool, carbon-rich ''stellar'' cores. Modest amounts of dust mass loss combine with the stellar spectral energy distribution to make these objects appear extreme in their near-infrared and mid-infrared colors. One object in our sample, HV 915, a known post-asymptotic giant branch star of the RV Tau type, exhibits CO 2.3 μm band head emission consistent with previous work that demonstrates that the object has a circumstellar disk.

  19. Spitzer SAGE-Spec: Near Infrared Spectroscopy, Dust Shells, and Cool Envelopes in Extreme Large Magellanic Cloud Asymptotic Giant Branch Stars

    NASA Astrophysics Data System (ADS)

    Blum, R. D.; Srinivasan, S.; Kemper, F.; Ling, B.; Volk, K.

    2014-11-01

    K-band spectra are presented for a sample of 39 Spitzer Infrared Spectrograph (IRS) SAGE-Spec sources in the Large Magellanic Cloud. The spectra exhibit characteristics in very good agreement with their positions in the near-infrared—Spitzer color-magnitude diagrams and their properties as deduced from the Spitzer IRS spectra. Specifically, the near-infrared spectra show strong atomic and molecular features representative of oxygen-rich and carbon-rich asymptotic giant branch stars, respectively. A small subset of stars was chosen from the luminous and red extreme ``tip" of the color-magnitude diagram. These objects have properties consistent with dusty envelopes but also cool, carbon-rich ``stellar" cores. Modest amounts of dust mass loss combine with the stellar spectral energy distribution to make these objects appear extreme in their near-infrared and mid-infrared colors. One object in our sample, HV 915, a known post-asymptotic giant branch star of the RV Tau type, exhibits CO 2.3 μm band head emission consistent with previous work that demonstrates that the object has a circumstellar disk. Based on observations obtained at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovação (MCTI) da República Federativa do Brasil, the U.S. National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU).

  20. Erratum: “Spitzer SAGE-Spec: Near Infrared Spectroscopy, Dust Shells, and Cool Envelopes in Extreme Large Magellanic Cloud Asymptotic Giant Branch Stars” (2014, AJ, 148, 86)

    NASA Astrophysics Data System (ADS)

    Blum, R. D.; Srinivasan, S.; Kemper, F.; Ling, B.; Volk, K.

    2015-02-01

    K-band spectra are presented for a sample of 39 Spitzer IRS SAGE-Spec sources in the Large Magellanic Cloud. The spectra exhibit characteristics in very good agreement with their positions in the near infrared - Spitzer color-magnitude diagrams and their properties as deduced from the Spitzer IRS spectra. Specifically, the near infrared spectra show strong atomic and molecular features representative of oxygen-rich and carbon-rich asymptotic giant branch stars, respectively. A small subset of stars were chosen from the luminous and red extreme "tip" of the color magnitude diagram. These objects have properties consistent with dusty envelopes but also cool, carbon-rich "stellar" cores. Modest amounts of dust mass loss combine with the stellar spectral energy distribution to make these objects appear extreme in their near infrared and mid infrared colors. One object in our sample, HV 915, a known post asymptotic giant branch star of the RV Tau type exhibits CO 2.3 micron band head emission consistent with previous work that demonstrates the object has a circumstellar disk.

  1. 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 carried out a search for optically visible post-asymptotic giant branch (post-AGB) candidates in the Small Magellanic Cloud (SMC). First, we used mid-IR observations from the Spitzer Space Telescope to select optically visible candidates with excess mid-IR flux and then we obtained low-resolution optical spectra for 801 of the candidates. After removing poor-quality spectra and contaminants, such as M-stars, C-stars, planetary nebulae, quasi-stellar objects and background galaxies, we ended up with a final sample of 63 high-probability post-AGB/RGB candidates of A-F spectral type. From the spectral observations, we estimated the stellar parameters: effective temperature (Teff), surface gravity (log g) and metallicity ([Fe/H]). We also estimated the reddening and deduced the luminosity using the stellar parameters combined with photometry. For the post-AGB/RGB candidates, we found that the metallicity distribution peaks at [Fe/H] ≈ -1.00 dex. Based on a luminosity criterion, 42 of these 63 sources were classified as post-red giant branch (post-RGB) candidates and the remaining 21 as post-AGB candidates. From the spectral energy distributions, we were able to infer that 6 of the 63 post-AGB/RGB candidates have a surrounding circumstellar shell suggesting that they are single stars, while 27 of the post-AGB/RGB candidates have a surrounding disc, suggesting that they lie in binary systems. For the remaining 30 post-AGB/RGB candidates the nature of the circumstellar environment was unclear. Variability is displayed by 38 of the 63 post-AGB/RGB candidates with the most common variability types being the Population II Cepheids (including RV-Tauri stars) and semiregular variables. This study has also revealed a new RV Tauri star in the SMC, J005107.19-734133.3, which shows signs of s-process enrichment. From the numbers of post-AGB/RGB stars in the SMC, we were able to estimate evolutionary rates. We find that the number of post-AGB and post-RGB candidates that

  2. Molecular processes from the AGB to the PN stage

    NASA Astrophysics Data System (ADS)

    García-Hernández, D. Anibal

    2012-08-01

    Many complex organic molecules and inorganic solid-state compounds have been observed in the circumstellar shell of stars (both C-rich and O-rich) in the transition phase between Asymptotic Giant Branch (AGB) stars and Planetary Nebulae (PNe). This short (~102-104 years) phase of stellar evolution represents a wonderful laboratory for astrochemistry and provides severe constraints on any model of gas-phase and solid-state chemistry. One of the major challenges of present day astrophysics and astrochemistry is to understand the formation pathways of these complex organic molecules and inorganic solid-state compounds (e.g., polycyclic aromatic hydrocarbons, fullerenes, and graphene in the case of a C-rich chemistry and oxides and crystalline silicates in O-rich environments) in space. In this review, I present an observational review of the molecular processes in the late stages of stellar evolution with a special emphasis on the first detections of fullerenes and graphene in 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. 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.

  5. 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.

  6. Nucleosynthesis in helium-enriched asymptotic giant branch models: Implications for Heavy Element Enrichment in ω Centauri

    NASA Astrophysics Data System (ADS)

    Karakas, Amanda; Shingles, Luke; Doherty, Carolyn Louise; Lattanzio, John; Fabiola Marino, Anna; Nataf, David

    2015-08-01

    Globular clusters are now known to harbour helium-rich stellar populations. While the stars we see today are all low mass, there were once stars of all mass ranges born in clusters with helium mass fractions up to Y ≈ 0.40. However, the effect of helium enrichment on the stellar evolution and nucleosynthesis of evolved intermediate-mass stars is still relatively unexplored. We calculate evolutionary sequences of intermediate-mass stars of low metallicity (M=1.7 to 6M⊙, Z = 0.0006 or [Fe/H] = -1.4) at primordial helium abundance (Y = 0.24) and with helium-enhanced compositions (Y = 0.30, 0.35, 0.40).We find the following: 1) The lifetime of helium-enriched stars is reduced by up to 50% compared to their helium normal counterparts, allowing for low-mass AGB stars to contribute to the chemical evolution of globular clusters; 2) The stellar yields of carbon, and heavy-elements typicallyproduced by low-mass AGB stars (e.g., Ba, La) decrease by ~50% in helium enriched models. 3) The initial mass required for carbon burning (and the transition to super AGB stars with ONe cores) at this metallicity is reduced from Mup > 6M⊙ at Y = 0.24 to Mup = 4.5 ± 0.5M⊙ at Y = 0.40. This will reduce the minimum mass for core collapse supernovae and increase the number of neutron stars. 4) The stellar yields of the helium-rich intermediate-mass stars with proton capture nucleosynthesis at the base of the envelope also decreases, with the most massive 6M⊙ model with Y = 0.40 experiencing almost no third dredge-up. The one exception is the 3M⊙ models, which produce more Ba, La, Ce, and Pb at Y = 0.40 than at Y = 0.24 due to the doubling of the number of thermal pulses.In this talk we present some highlights of our results along with a discussion of the implications for the formation of massive globular clusters.

  7. 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.

  8. A TEMPORAL STUDY OF THE OXYGEN-RICH PULSATING VARIABLE ASYMPTOTIC GIANT BRANCH STAR, T Cep: INVESTIGATION ON DUST FORMATION AND DUST PROPERTIES

    SciTech Connect

    Guha Niyogi, Suklima; Speck, Angela K.; Onaka, Takashi

    2011-06-01

    Pulsation is believed to be the leading cause of dusty mass loss from asymptotic giant branch stars. We present a temporal study of T Cep, a long-period Mira variable, using seven Infrared Space Observatory Short Wavelength Spectrometer spectra, covering a 16 month period over a single pulsation cycle. The observed spectral dust features change over the pulsation cycle of this Mira. In general, the overall apparent changes in spectral features can be attributed to changes in the dust temperature, resulting from the intrinsic pulsation cycle of the central star. However, not all feature changes are so easily explained. Based on direct comparison with laboratory spectra of several potential minerals, the dust is best explained by crystalline iron-rich silicates. These findings contradict the currently favored dust formation hypotheses.

  9. 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

  10. 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.

  11. Is the 21-micron Feature Observed in Some Post-AGB Stars Caused by the Interaction Between Ti Atoms and Fullerenes?

    NASA Technical Reports Server (NTRS)

    Kimura, Yuki; Nuth, Joseph A. III; Ferguson, Frank T.

    2005-01-01

    Recent measurements of fullerenes and Ti atoms recorded in our laboratory have demonstrated the presence of an infrared feature near 21 pm. The feature observed has nearly the same shape and position as is observed for one of the most enigmatic features in post-asymptotic giant blanch (AGB) stars. In our experimental system large cage carbon particles, such as large fullerenes, were produced from CO gas by the Boudouard reaction. Large-cage carbon particles intermixed with Ti atoms were produced by the evaporation of a Ti metal wrapped carbon electrode in CO gas. The infrared spectra of large fullerenes interacting with Ti atoms show a characteristic feature at 20.3 micron that closely corresponds to the 20.1 micron feature observed in post-AGB stars. Both the lab- oratory and stellar spectra also show a small but significant peak at 19.0 micron, which is attributed to fullerenes. Here, we propose that the interaction between fullerenes and Ti atoms may be a plausible explanation for the 21-micron feature seen in some post-AGB stars.

  12. 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

  13. 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

  14. EFFECT OF HIGH-ENERGY RESONANCES ON THE {sup 18}O(p, {alpha}){sup 15}N REACTION RATE AT AGB AND POST-AGB RELEVANT TEMPERATURES

    SciTech Connect

    La Cognata, M.; Spitaleri, C.; Mukhamedzhanov, A. M.

    2010-11-10

    The {sup 18}O(p, {alpha}){sup 15}N reaction is of great importance in several astrophysical scenarios, as it influences the production of key isotopes such as {sup 19}F, {sup 18}O, and {sup 15}N. Fluorine is synthesized in the intershell region of asymptotic giant branch (AGB) stars, together with s-elements, by {alpha} radiative capture on {sup 15}N, which in turn is produced in the {sup 18}O proton-induced destruction. Peculiar {sup 18}O abundances are observed in R-Coronae Borealis stars, having {sup 16}O/{sup 18}O {approx}< 1, hundreds of times smaller than the galactic value. Finally, there is no definite explanation of the {sup 14}N/{sup 15}N ratio in pre-solar grains formed in the outer layers of AGB stars. Again, such an isotopic ratio is influenced by the {sup 18}O(p, {alpha}){sup 15}N reaction. In this work, a high accuracy {sup 18}O(p, {alpha}){sup 15}N reaction rate is proposed, based on the simultaneous fit of direct measurements and of the results of a new Trojan Horse experiment. Indeed, current determinations are uncertain because of the poor knowledge of the resonance parameters of key levels of {sup 19}F. In particular, we have focused on the study of the broad 660 keV 1/2{sup +} resonance corresponding to the 8.65 MeV level of {sup 19}F. Since {Gamma} {approx} 100-300 keV, it determines the low-energy tail of the resonant contribution to the cross section and dominates the cross section at higher energies. Here, we provide a reaction rate that is a factor of two larger above T {approx} 0.5 10{sup 9} K based on our new improved determination of its resonance parameters, which could strongly influence present-day astrophysical model predictions.

  15. 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.

  16. 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.

  17. Modelling a set of C-rich AGB stars: the cases of RU Vir and R Lep

    NASA Astrophysics Data System (ADS)

    Rau, G.; Paladini, C.; Hron, J.; Aringer, B.; Groenewegen, M. A. T.; Nowotny, W.

    We study the atmospheres of a set of carbon-rich asymptotic giant branch AGB stars to improve our understanding of the dynamic processes happening there. We compare in a systematic way spectrometric, photometric and mid-infrared (VLTI/MIDI) interferometric measurements with different types of model atmospheres: (1) hydrostatic models + MOD-dusty models added a posteriori; (2) self-consistent dynamic model atmospheres. These allow us to interpret in a coherent way the dynamic behavior of gas and dust. The results underline that the joint use of different kinds of observations, as photometry, spectroscopy and interferometry, is essential for understanding the atmospheres of pulsating C-rich AGB stars. For our first target, the carbon-rich Mira star RU Vir, the dynamic model atmospheres fit well the ISO/SWS spectrum in the wavelength range lambda = [2.9, 13.0] mu m. However, the object turned out to be somehow ''peculiar''. The other target we present is R Lep. Here the agreement between models and observations is much better although the MIDI data at 11.4 mu m cannot be properly modelled.

  18. A Photometric and Spectroscopic Survey of AGB Stars in M31

    NASA Astrophysics Data System (ADS)

    Brewer, James P.

    1996-04-01

    Asymptotic giant-branch (AGB) stars are identified and classified in five 7' X 7' fields spaced along M31's SW semi-major axis using a four band photometric system. An investigation of the AGB luminosity functions and red giant-branch widths reveals significant differences between the star forming histories of the five fields. The distance modulus of M31 is derived using carbon stars (C-stars) and found to be consistent with both a value obtained from Cepheids and with values in the literature. The ratio of AGB C- to M-stars (C/M ratio) in the five fields is found to increase with galactocentric distance and it is shown that photometric incompleteness is not responsible for this effect. This is the first clear demonstration of a varying C/M ratio in an external galaxy. The C/M ratios appear to be insensitive to star-forming history differences but sensitive to metallicity differences between the fields. Previous observations are used to define a relationship between the C/M ratio and metallicity, and this is used to obtain estimates of the field metallicities. These estimates are found to be consistent with a previous measurement of M31's metallicity gradient. The C/M ratios measured in M31 indicate that the composition of M31's interstellar medium may be position dependent, and evidence is cited in favour of this. Follow up spectroscopy was obtained in two of the five fields, and is used to show that the photometric system did an excellent job of discriminating between M-, S- and C-stars. Of the 48 C-stars for which spectra were obtained, 7 have strongly enhanced 13C bands (J-stars), 2 have strong H-alpha emission, while 3 are found to exhibit enhanced Li absorption (Li-stars). Both the J- and Li-stars are fainter than predicted by current theoretical models, while the colours of the H-alpha stars suggest they may be in the terminal phases of their evolution. The C_2 and CN bandstrengths of the C-stars are measured, and no correlation between these bandstrengths

  19. A Photometric and Spectroscopic Survey of AGB Stars in M31

    NASA Astrophysics Data System (ADS)

    Brewer, James Philip

    1996-01-01

    Asymptotic giant-branch (AGB) stars are identified and classified in five 7^'times7 ^' fields spaced along M31's SW semi-major axis using a four band photometric system. An investigation of the AGB luminosity functions and red giant -branch widths reveals significant differences between the star forming histories of the five fields. The distance modulus of M31 is derived using carbon stars (C-stars) and found to be consistent with both a value obtained from Cepheids and with values in the literature. The ratio of AGB C- to M-stars (C/M ratio) in the five fields is found to increase with galactocentric distance and it is shown that photometric incompleteness is not responsible for this effect. This is the first clear demonstration of a varying C/M ratio in an external galaxy. The C/M ratios appear to be insensitive to star -forming history differences but sensitive to metallicity differences between the fields. Previous observations are used to define a relationship between the C/M ratio and metallicity, and this is used to obtain estimates of the field metallicities. These estimates are found to be consistent with a previous measurement of M31's metallicity gradient. The C/M ratios measured in M31 indicate that the composition of M31's interstellar medium may be position dependent, and evidence is cited in favour of this. Follow up spectroscopy was obtained in two of the five fields, and is used to show that the photometric system did an excellent job of discriminating between M -, S- and C-stars. Of the 48 C-stars for which spectra were obtained, 7 have strongly enhanced ^ {13}C bands (J-stars), 2 have strong H alpha emission, while 3 are found to exhibit enhanced Li absorption (Li-stars). Both the J- and Li-stars are fainter than predicted by current theoretical models, while the colours of the Hα stars suggest they may be in the terminal phase of their evolution. The C_2 and CN bandstrengths of the C-stars are measured, and no correlation between these

  20. 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).

  1. Sublimating comets as the source of nucleation seeds for grain condensation in the gas outflow from AGB stars

    NASA Technical Reports Server (NTRS)

    Whitmire, D. P.; Matese, John J.; Reynolds, R. T.

    1989-01-01

    A growing amount of observational and theoretical evidence suggests that most main sequence stars are surrounded by disks of cometary material. The dust production by comets in such disks is investigated when the central stars evolve up the red giant and asymptotic giant branch (AGB). Once released, the dust is ablated and accelerated by the gas outflow and the fragments become the seeds necessary for condensation of the gas. The origin of the requisite seeds has presented a well known problem for classical nucleation theory. This model is consistent with the dust production observed in M giants and supergiants (which have increasing luminosities) and the fact that earlier supergiants and most WR stars (whose luminosities are unchanging) do not have significant dust clouds even though they have significant stellar winds. Another consequence of the model is that the spatial distribution of the dust does not, in general, coincide with that of the gas outflow, in contrast to the conventional condensation model. A further prediction is that the condensation radius is greater that that predicted by conventional theory which is in agreement with IR interferometry measurements of alpha-Ori.

  2. 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, originating from asymptotic giant branch (AGB) stars, 32 had high enough Ba contents for isotopic analysis. For 26 of them, CsHx interferences were either negligible or could be corrected with confidence. They exhibit typical s-process Ba isotopic patterns with slightly higher than solar 134Ba/136Ba and lower than solar 135,137,138Ba/136Ba ratios. Results are generally well explained in the context of neutron capture nucleosynthesis in low mass (1-3 M⊙) AGB stars and provide constraints on AGB models, by reducing the needed 13C spread from factor of ˜20 down to 2. Out of the 19 supernova X grains, three had sufficient concentrations for isotopic analysis. They tend to exhibit higher than solar 134Ba/136Ba and 138Ba/136Ba ratios, close to solar 137Ba/136Ba, and 135Ba/136Ba lower than solar but higher than in mainstream grains. This signature could indicate a mixture of n-burst type Ba with either "normal Ba" more s-process-rich than solar, or normal Ba plus weak s-process Ba. In the n-burst component Cs may have to be separated from Ba at ˜10 years after the SN explosion. Depending on predictions for its composition, another possibility is early separation (at ˜1 year) coupled with addition of some unfractionated n-burst matter. Abundances of trace elements (Sr, Zr, Cs, La, and Ce) analyzed along with Ba signify that implantation may have been an important process for their introduction.

  3. New Determination of the 13C(α, n)16O Reaction Rate and its Influence on the s-process Nucleosynthesis in AGB Stars

    NASA Astrophysics Data System (ADS)

    Guo, B.; Li, Z. H.; Lugaro, M.; Buntain, J.; Pang, D. Y.; Li, Y. J.; Su, J.; Yan, S. Q.; Bai, X. X.; Chen, Y. S.; Fan, Q. W.; Jin, S. J.; Karakas, A. I.; Li, E. T.; Li, Z. C.; Lian, G.; Liu, J. C.; Liu, X.; Shi, J. R.; Shu, N. C.; Wang, B. X.; Wang, Y. B.; Zeng, S.; Liu, W. P.

    2012-09-01

    We present a new measurement of the α-spectroscopic factor (S α) and the asymptotic normalization coefficient for the 6.356 MeV 1/2+ subthreshold state of 17O through the 13C(11B, 7Li)17O transfer reaction and we determine the α-width of this state. This is believed to have a strong effect on the rate of the 13C(α, n)16O reaction, the main neutron source for slow neutron captures (the s-process) in asymptotic giant branch (AGB) stars. Based on the new width we derive the astrophysical S-factor and the stellar rate of the 13C(α, n)16O reaction. At a temperature of 100 MK, our rate is roughly two times larger than that by Caughlan & Fowler and two times smaller than that recommended by the NACRE compilation. We use the new rate and different rates available in the literature as input in simulations of AGB stars to study their influence on the abundances of selected s-process elements and isotopic ratios. There are no changes in the final results using the different rates for the 13C(α, n)16O reaction when the 13C burns completely in radiative conditions. When the 13C burns in convective conditions, as in stars of initial mass lower than ~2 M ⊙ and in post-AGB stars, some changes are to be expected, e.g., of up to 25% for Pb in our models. These variations will have to be carefully analyzed when more accurate stellar mixing models and more precise observational constraints are available.

  4. On the Giant Horizontal and Asymptotic Branches of Galactic Globular Clusters - Part Five - CCD Photometry of NGC1261

    NASA Astrophysics Data System (ADS)

    Ferraro, F. R.; Clementini, G.; Fusi-Pecci, F.; Vitiello, E.; Buonanno, R.

    1993-09-01

    BV CCD photometry is presented for 3352 stars (18 variables) in the globular cluster NGC 126 t. The main conclusions drawn from the structure of the colour-magnitude diagram (CMD) are as follows. (i) The location and structure of the main branches agree with those found in previous studies, confirming the existence of a well-defined blue horizontal branch (1113) tail in addition to the large number of red 1113 stars. (ii) The mean metallicity derived from CMD indicators calibrated with the Zinn & West scale is [Fe/H] = -1.4±0.2, and the very small intrinsic width of the various branches yields very low upper limits (Δ[Fe/H]≤0.06, Δ[CNO]≤-0.2) for any chemical abundance spread. (iii) The `RGB bump' is detected at V= 16.70±0.05 as a clump of stars in the luminosity function of the red giant branch. (iv) VHB=16.70±0.04 and VTO=20.t4±0.10 yield ΔVTOHB=3.44±0.12. A detailed comparison with the main CMD loci of NGC 288 (a cluster that has similar metallicity but a totally blue 1113) throws doubt on the hypothesis that a clear difference in age (NGC 288 being older) is the `second parameter' necessary to explain the observed differences. (v) Some evidence is found for differences in the spatial distribution of the red and blue 1113 stars that is worthy of further analysis.

  5. The dust disk and companion of the nearby AGB star L2 Puppis. SPHERE/ZIMPOL polarimetric imaging at visible wavelengths

    NASA Astrophysics Data System (ADS)

    Kervella, P.; Montargès, M.; Lagadec, E.; Ridgway, S. T.; Haubois, X.; Girard, J. H.; Ohnaka, K.; Perrin, G.; Gallenne, A.

    2015-06-01

    The bright southern star L2 Pup is a particularly prominent asymptotic giant branch (AGB) star, located at a distance of only 64 pc. We report new adaptive optics observations of L2 Pup at visible wavelengths with the SPHERE/ZIMPOL instrument of the VLT that confirm the presence of the circumstellar dust disk discovered recently. This disk is seen almost almost edge-on at an inclination of 82◦. The signature of its three-dimensional structure is clearly observed in the map of the degree of linear polarization pL. We identify the inner rim of the disk through its polarimetric signature at a radius of 6 AU from the AGB star. The ZIMPOL intensity images in the V and R bands also reveal a close-in secondary source at a projected separation of 2 AU from the primary. Identification of the spectral type of this companion is uncertain due to the strong reddening from the disk, but its photometry suggests that it is a late K giant with comparable mass to the AGB star. We present refined physical parameters for the dust disk derived using the RADMC-3D radiative transfer code. We also interpret the pL map using a simple polarization model to infer the three-dimensional structure of the envelope. Interactions between the inner binary system and the disk apparently form spiral structures that propagate along the orthogonal axis to the disk to form streamers. Two dust plumes propagating orthogonally to the disk are also detected. They originate in the inner stellar system and are possibly related to the interaction of the wind of the two stars with the material in the disk. Based on the morphology of the envelope of L2 Pup, we propose that this star is at an early stage in the formation of a bipolar planetary nebula. Based on observations made with ESO telescopes at Paranal Observatory, under ESO Science Verification program 60.A-9367(A).

  6. 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

  7. Near-infrared and Brγ observations of post-AGB stars

    NASA Astrophysics Data System (ADS)

    Van de Steene, G. C.; van Hoof, P. A. M.; Wood, P. R.

    2000-10-01

    Brgamma emission originates in the post-Asymptotic Giant Branch (post-AGB) wind, and that the central star is not yet hot enough to ionize the AGB shell. We measured the J H K L magnitudes of the objects and present their infrared spectral energy distributions. They are typical for post-AGB stars according to the scheme of van der Veen et al. (\\cite{vdVeen89}). We also constructed various color-color diagrams using the near-infrared and IRAS magnitudes. No distinction can be made between the objects showing Brgamma in emission, absorption, or a flat spectrum in the near and far-infrared color-color diagrams. The near-infrared color-color diagrams show evidence for a very large range of extinction, which in part is of circumstellar origin. Near-infrared versus far-infrared color-color diagrams show trends that are consistent with the expected evolution of the circumstellar shell. This sample of post-AGB stars show a larger range in color and are generally redder and closer to the galactic plane than the ones known so far. The properties of most of these objects are fully consistent with the assumption that they are post-AGB stars that have not evolved far enough yet to ionize a significant fraction of their circumstellar material. Based on observations made at the European Southern Observatory, La Silla, Chile; the Australia Telescope Compact Array, which is funded by the Commonwealth of Australia for operations as a National Facility managed by CSIRO; Siding Spring Observatory.

  8. A Study of the λ10830 He I Line Among Red Giants in Messier 13

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    Two properties of Messier 13 are pertinent to the study of mass loss among metal-poor stars and the chemical evolution of globular clusters: (1) an extended blue horizontal branch, which seems to demand mass loss from red giant progenitor stars and possibly an enhanced helium abundance, and (2) the presence of internal abundance inhomogeneities of elements in the mass range from C to Al. A popular explanation for this second phenomenon is that M13 was self-enriched by intermediate-mass asymptotic giant branch (IM-AGB) stars of a type that may also have been able to instigate helium enrichment. Spectra of the λ10830 absorption feature produced by He I have been obtained by using the NIRSPEC spectrometer on the Keck 2 telescope for seven red giants in M13 chosen to have a range in λ3883 CN band strengths, oxygen, and sodium abundances. Whereas these spectra do reveal the presence of fast winds among some M13 red giants, they provide little support for helium abundance differences of the type that might have been generated by a burst of IM-AGB star activity within the M13 protocluster. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

  9. 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.

  10. CHEMICAL ABUNDANCES IN FIELD RED GIANTS FROM HIGH-RESOLUTION H-BAND SPECTRA USING THE APOGEE SPECTRAL LINELIST

    SciTech Connect

    Smith, Verne V.; Cunha, Katia; Shetrone, Matthew D.; Meszaros, Szabolcs; Allende Prieto, Carlos; Bizyaev, Dmitry; Garcia Perez, Ana; Majewski, Steven R.; Schiavon, Ricardo; Holtzman, Jon; Johnson, Jennifer A.

    2013-03-01

    High-resolution H-band spectra of five bright field K, M, and MS giants, obtained from the archives of the Kitt Peak National Observatory Fourier transform spectrometer, are analyzed to determine chemical abundances of 16 elements. The abundances were derived via spectrum synthesis using the detailed linelist prepared for the Sloan Digital Sky Survey III Apache Point Galactic Evolution Experiment (APOGEE), which is a high-resolution near-infrared spectroscopic survey to derive detailed chemical abundance distributions and precise radial velocities for 100,000 red giants sampling all Galactic stellar populations. The red giant sample studied here was chosen to probe which chemical elements can be derived reliably from the H-band APOGEE spectral region. These red giants consist of two K-giants ({alpha} Boo and {mu} Leo), two M-giants ({beta} And and {delta} Oph), and one thermally pulsing asymptotic giant branch (TP-AGB) star of spectral type MS (HD 199799). Measured chemical abundances include the cosmochemically important isotopes {sup 12}C, {sup 13}C, {sup 14}N, and {sup 16}O, along with Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu. The K and M giants exhibit the abundance signature of the first dredge-up of CN-cycle material, while the TP-AGB star shows clear evidence of the addition of {sup 12}C synthesized during {sup 4}He-burning thermal pulses and subsequent third dredge-up. A comparison of the abundances derived here with published values for these stars reveals consistent results to {approx}0.1 dex. The APOGEE spectral region and linelist is thus well suited for probing both Galactic chemical evolution, as well as internal nucleosynthesis and mixing in populations of red giants via high-resolution spectroscopy.

  11. EFFECT OF METALLICITY ON THE EVOLUTION OF THE HABITABLE ZONE FROM THE PRE-MAIN SEQUENCE TO THE ASYMPTOTIC GIANT BRANCH AND THE SEARCH FOR LIFE

    SciTech Connect

    Danchi, William C.; Lopez, Bruno E-mail: bruno.lopez@oca.eu

    2013-05-20

    During the course of stellar evolution, the location and width of the habitable zone changes as the luminosity and radius of the star evolves. The duration of habitability for a planet located at a given distance from a star is greatly affected by the characteristics of the host star. A quantification of these effects can be used observationally in the search for life around nearby stars. The longer the duration of habitability, the more likely it is that life has evolved. The preparation of observational techniques aimed at detecting life would benefit from the scientific requirements deduced from the evolution of the habitable zone. We present a study of the evolution of the habitable zone around stars of 1.0, 1.5, and 2.0 M{sub Sun} for metallicities ranging from Z = 0.0001 to Z = 0.070. We also consider the evolution of the habitable zone from the pre-main sequence until the asymptotic giant branch is reached. We find that metallicity strongly affects the duration of the habitable zone for a planet as well as the distance from the host star where the duration is maximized. For a 1.0 M{sub Sun} star with near solar metallicity, Z = 0.017, the duration of the habitable zone is >10 Gyr at distances 1.2-2.0 AU from the star, whereas the duration is >20 Gyr for high-metallicity stars (Z = 0.070) at distances of 0.7-1.8 AU, and {approx}4 Gyr at distances of 1.8-3.3 AU for low-metallicity stars (Z = 0.0001). Corresponding results have been obtained for stars of 1.5 and 2.0 solar masses.

  12. 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.

  13. 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

  14. Polynomial Asymptotes

    ERIC Educational Resources Information Center

    Dobbs, David E.

    2010-01-01

    This note develops and implements the theory of polynomial asymptotes to (graphs of) rational functions, as a generalization of the classical topics of horizontal asymptotes and oblique/slant asymptotes. Applications are given to hyperbolic asymptotes. Prerequisites include the division algorithm for polynomials with coefficients in the field of…

  15. 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

  16. 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.

  17. 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).

  18. 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.

  19. Oxygen- and carbon-rich variable red giant populations in the Magellanic Clouds from EROS, OGLE, MACHO, and 2MASS photometry

    NASA Astrophysics Data System (ADS)

    Wiśniewski, M.; Marquette, J. B.; Beaulieu, J. P.; Schwarzenberg-Czerny, A.; Tisserand, P.; Lesquoy, É.

    2011-06-01

    Context. The carbon-to-oxygen (C/O) ratio of asymptotic giant branch (AGB) stars constitutes an important index of evolutionary and environment/metallicity factor. Aims: We develop a method for mass C/O classification of AGBs in photometric surveys without using periods. Methods: For this purpose we rely on the slopes in the tracks of individual stars in the colour-magnitude diagram. Results: We demonstrate that our method enables the separation of C-rich and O-rich AGB stars with little confusion. For the Magellanic Clouds we demonstrate that this method works for several photometric surveys and filter combinations. As we rely on no period identification, our results are relatively insensitive to the phase coverage, aliasing, and time-sampling problems that plague period analyses. For a subsample of our stars, we verify our C/O classification against published C/O catalogues. With our method we are able to produce C/O maps of the entire Magellanic Clouds. Conclusions: Our purely photometric method for classification of C- and O-rich AGBs constitutes a method of choice for large, near-infrared photometric surveys. Because our method depends on the slope of colour-magnitude variation but not on magnitude zero point, it remains applicable to objects with unknown distances.

  20. A Comparative Study of Two 47 Tuc Giant Stars with Different s-process Enrichment

    NASA Astrophysics Data System (ADS)

    Cordero, M. J.; Hansen, C. J.; Johnson, C. I.; Pilachowski, C. A.

    2015-07-01

    Here we aim to understand the origin of 47 Tuc’s La-rich star Lee 4710. We report abundances for O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Co, Ni, Zn, Y, Zr, Ba, La, Ce, Pr, Nd, and Eu and present a detailed abundance analysis of two 47 Tuc stars with similar stellar parameters but different slow neutron-capture (s-)process enrichment. Star Lee 4710 has the highest known La abundance ratio in this cluster ([La/Fe] = 1.14), and star Lee 4626 is known to have normal s-process abundances (e.g., [Ba/Eu] < 0). The nucleosynthetic pattern of elements with Z ≳ 56 for star Lee 4710 agrees with the predicted yields of a 1.3{M}⊙ asymptotic giant branch (AGB) star. Therefore, Lee 4710 may have been enriched by mass transfer from a more massive AGB companion, which is compatible with its location far away from the center of this relatively metal-rich ([Fe/H] ˜ -0.7) globular cluster. A further analysis comparing the abundance pattern of Lee 4710 with data available in the literature reveals that nine out of the ˜200 47 Tuc stars previously studied show strong s-process enhancements that point toward later enrichment by more massive AGB stars.

  1. Magnetic fields in single late-type giants in the Solar vicinity: How common is magnetic activity on the giant branches?

    NASA Astrophysics Data System (ADS)

    Konstantinova-Antova, Renada; Aurière, Michel; Charbonnel, Corinne; Drake, Natalia; Wade, Gregg; Tsvetkova, Svetla; Petit, Pascal; Schröder, Klaus-Peter; Lèbre, Agnes

    2014-08-01

    We present our first results on a new sample containing all single G, K and M giants down to V = 4 mag in the Solar vicinity, suitable for spectropolarimetric (Stokes V) observations with Narval at TBL, France. For detection and measurement of the magnetic field (MF), the Least Squares Deconvolution (LSD) method was applied (Donati et al. 1997) that in the present case enables detection of large-scale MFs even weaker than the solar one (the typical precision of our longitudinal MF measurements is 0.1-0.2 G). The evolutionary status of the stars is determined on the basis of the evolutionary models with rotation (Lagarde et al. 2012; Charbonnel et al., in prep.) and fundamental parameters given by Massarotti et al. (1998). The stars appear to be in the mass range 1-4 M ⊙, situated at different evolutionary stages after the Main Sequence (MS), up to the Asymptotic Giant Branch (AGB). The sample contains 45 stars. Up to now, 29 stars are observed (that is about 64% of the sample), each observed at least twice. For 2 stars in the Hertzsprung gap, one is definitely Zeeman detected. Only 5 G and K giants, situated mainly at the base of the Red Giant Branch (RGB) and in the He-burning phase are detected. Surprisingly, a lot of stars ascending towards the RGB tip and in early AGB phase are detected (8 of 13 observed stars). For all Zeeman detected stars v sin i is redetermined and appears in the interval 2-3 km/s, but few giants with MF possess larger v sin i.

  2. Application of a Theory and Simulation-based Convective Boundary Mixing Model for AGB Star Evolution and Nucleosynthesis

    NASA Astrophysics Data System (ADS)

    Battino, U.; Pignatari, M.; Ritter, C.; Herwig, F.; Denisenkov, P.; Den Hartogh, J. W.; Trappitsch, R.; Hirschi, R.; Freytag, B.; Thielemann, F.; Paxton, B.

    2016-08-01

    The s-process nucleosynthesis in Asymptotic giant branch (AGB) stars depends on the modeling of convective boundaries. We present models and s-process simulations that adopt a treatment of convective boundaries based on the results of hydrodynamic simulations and on the theory of mixing due to gravity waves in the vicinity of convective boundaries. Hydrodynamics simulations suggest the presence of convective boundary mixing (CBM) at the bottom of the thermal pulse-driven convective zone. Similarly, convection-induced mixing processes are proposed for the mixing below the convective envelope during third dredge-up (TDU), where the {}13{{C}} pocket for the s process in AGB stars forms. In this work, we apply a CBM model motivated by simulations and theory to models with initial mass M = 2 and M=3 {M}ȯ , and with initial metal content Z = 0.01 and Z = 0.02. As reported previously, the He-intershell abundances of {}12{{C}} and {}16{{O}} are increased by CBM at the bottom of the pulse-driven convection zone. This mixing is affecting the {}22{Ne}(α, n){}25{Mg} activation and the s-process efficiency in the {}13{{C}}-pocket. In our model, CBM at the bottom of the convective envelope during the TDU represents gravity wave mixing. Furthermore, we take into account the fact that hydrodynamic simulations indicate a declining mixing efficiency that is already about a pressure scale height from the convective boundaries, compared to mixing-length theory. We obtain the formation of the {}13{{C}}-pocket with a mass of ≈ {10}-4 {M}ȯ . The final s-process abundances are characterized by 0.36\\lt [{{s}}/{Fe}]\\lt 0.78 and the heavy-to-light s-process ratio is -0.23\\lt [{hs}/{ls}]\\lt 0.45. Finally, we compare our results with stellar observations, presolar grain measurements and previous work.

  3. The Keck Aperture Masking Experiment: Dust Enshrouded Red Giants

    NASA Technical Reports Server (NTRS)

    Blasius, T. D.; Monnier, J. D.; Tuthill, P. G.; Danchi, W. C.; Anderson, M.

    2012-01-01

    While the importance of dusty asymptotic giant branch (AGB) stars to galactic chemical enrichment is widely recognised, a sophisticated understanding of the dust formation and wind-driving mechanisms has proven elusive due in part to the difficulty in spatially-resolving the dust formation regions themselves. We have observed twenty dust-enshrouded AGB stars as part of the Keck Aperture Masking Experiment, resolving all of them in multiple near-infrared bands between 1.5 m and 3.1 m. We find 45% of the targets to show measurable elongations that, when correcting for the greater distances of the targets, would correspond to significantly asymmetric dust shells on par with the well-known cases of IRC +10216 or CIT 6. Using radiative transfer models, we find the sublimation temperature of Tsub(silicates) = 1130 90K and Tsub(amorphous carbon) = 1170 60 K, both somewhat lower than expected from laboratory measurements and vastly below temperatures inferred from the inner edge of YSO disks. The fact that O-rich and C-rich dust types showed the same sublimation temperature was surprising as well. For the most optically-thick shells ( 2.2 m > 2), the temperature profile of the inner dust shell is observed to change substantially, an effect we suggest could arise when individual dust clumps become optically-thick at the highest mass-loss rates.

  4. Detailed homogeneous abundance studies of 14 Galactic s-process enriched post-AGB stars: In search of lead (Pb)

    NASA Astrophysics Data System (ADS)

    De Smedt, K.; Van Winckel, H.; Kamath, D.; Siess, L.; Goriely, S.; Karakas, A. I.; Manick, R.

    2016-03-01

    Context. This paper is part of a larger project in which we systematically study the chemical abundances of Galactic and extragalactic post-asymptotic giant branch (post-AGB) stars. The goal at large is to provide improved observational constraints to the models of the complex interplay between the AGB s-process nucleosynthesis and the associated mixing processes. Aims: Lead (Pb) is the final product of the s-process nucleosynthesis and is predicted to have large overabundances with respect to other s-process elements in AGB stars of low metallicities. However, Pb abundance studies of s-process enriched post-AGB stars in the Magellanic Clouds show a discrepancy between observed and predicted Pb abundances. The determined upper limits based on spectral studies are much lower than what is predicted. In this paper, we focus specifically on the Pb abundance of 14 Galactic s-process enhanced post-AGB stars to check whether the same discrepancy is present in the Galaxy as well. Among these 14 objects, two were not yet subject to a detailed abundance study in the literature. We apply the same method to obtain accurate abundances for the 12 others. Our homogeneous abundance results provide the input of detailed spectral synthesis computations in the spectral regions where Pb lines are located. Methods: We used high-resolution UVES and HERMES spectra for detailed spectral abundance studies of our sample of Galactic post-AGB stars. None of the sample stars display clear Pb lines, and we only deduced upper limits of the Pb abundance by using spectrum synthesis in the spectral ranges of the strongest Pb lines. Results: We do not find any clear evidence of Pb overabundances in our sample. The derived upper limits are strongly correlated with the effective temperature of the stars with increasing upper limits for increasing effective temperatures. We obtain stronger Pb constraints on the cooler objects. Moreover, we confirm the s-process enrichment and carbon enhancement of two

  5. Detailed homogeneous abundance studies of 14 Galactic s-process enriched post-AGB stars: In search of lead (Pb)

    NASA Astrophysics Data System (ADS)

    De Smedt, K.; Van Winckel, H.; Kamath, D.; Siess, L.; Goriely, S.; Karakas, A. I.; Manick, R.

    2016-03-01

    Context. This paper is part of a larger project in which we systematically study the chemical abundances of Galactic and extragalactic post-asymptotic giant branch (post-AGB) stars. The goal at large is to provide improved observational constraints to the models of the complex interplay between the AGB s-process nucleosynthesis and the associated mixing processes. Aims: Lead (Pb) is the final product of the s-process nucleosynthesis and is predicted to have large overabundances with respect to other s-process elements in AGB stars of low metallicities. However, Pb abundance studies of s-process enriched post-AGB stars in the Magellanic Clouds show a discrepancy between observed and predicted Pb abundances. The determined upper limits based on spectral studies are much lower than what is predicted. In this paper, we focus specifically on the Pb abundance of 14 Galactic s-process enhanced post-AGB stars to check whether the same discrepancy is present in the Galaxy as well. Among these 14 objects, two were not yet subject to a detailed abundance study in the literature. We apply the same method to obtain accurate abundances for the 12 others. Our homogeneous abundance results provide the input of detailed spectral synthesis computations in the spectral regions where Pb lines are located. Methods: We used high-resolution UVES and HERMES spectra for detailed spectral abundance studies of our sample of Galactic post-AGB stars. None of the sample stars display clear Pb lines, and we only deduced upper limits of the Pb abundance by using spectrum synthesis in the spectral ranges of the strongest Pb lines. Results: We do not find any clear evidence of Pb overabundances in our sample. The derived upper limits are strongly correlated with the effective temperature of the stars with increasing upper limits for increasing effective temperatures. We obtain stronger Pb constraints on the cooler objects. Moreover, we confirm the s-process enrichment and carbon enhancement of two

  6. A newly discovered stellar type: dusty post-red giant branch stars in the Magellanic Clouds

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    Context. We present a newly discovered class of low-luminosity, dusty, evolved objects in the Magellanic Clouds. These objects have dust excesses, stellar parameters, and spectral energy distributions similar to those of dusty post-asymptotic giant branch (post-AGB) stars. However, they have lower luminosities and hence lower masses. We suggest that they have evolved off the red giant branch (RGB) instead of the AGB as a result of binary interaction. Aims: In this study we aim to place these objects in an evolutionary context and establish an evolutionary connection between RGB binaries (such as the sequence E variables) and our new sample of objects. Methods: We compared the theoretically predicted birthrates of the progeny of RGB binaries to the observational birthrates of the new sample of objects. Results: We find that there is order-of-magnitude agreement between the observed and predicted birthrates of post-RGB stars. The sources of uncertainty in the birthrates are discussed; the most important sources are probably the observational incompleteness factor and the post-RGB evolution rates. We also note that mergers are relatively common low on the RGB and that stars low on the RGB with mid-IR excesses may recently have undergone a merger. Conclusions: Our sample of dusty post-RGB stars most likely provides the first observational evidence for a newly discovered phase in binary evolution: post-RGB binaries with circumstellar dust.

  7. The pathways of C: from AGB stars, to the Interstellar Medium, and finally into the protoplanetary disk

    NASA Astrophysics Data System (ADS)

    Trigo-Rodriguez, J. M.; Garcia-Hernandez, D. A.

    2011-05-01

    The origin, and role of C in the formation of first solar system aggregates is described. Stellar grains evidence demonstrates that Asymptotic Giant Branch (AGB) stars were nearby to the solar nebula at the time of solar system formation. Such stars continue to burn H and He in shells that surround the C-O core. During their evolution, flashes occur in the He shell and the C, and O produced are eventually dredged up into the star's envelop and then to the stellar surface, and finally masively ejected to the interstellar medium (IM). Once in a molecular cloud, the electrophilicity of C makes this element reactable with the surrounding gas to produce different molecular species. Primitive meteorites, particularly these known as chondrites, preserved primeval materials of the disk. The abundances of short-lived radionuclides (SLN), inferred to have been present in the early solar system (ESS), are a constraint on the birth and early evolution of the solar system as their relatively short half lives do not allow the observed abundances to be explained by galactic chemical evolution processes. We present a model of a 6.5 solar masses star of solar metallicity that simultaneously match the abundances of SLNs inferred to have been present in the ESS by using a dilution factor of 1 part of AGB material per 300 parts of original solar nebula material, and taking into account a time interval between injection of SLNs and consolidation of chondrites equal to 0.53 Myr [2]. Such a polluting source does not overproduce 53Mn, as supernova models do, and only marginally affects isotopic ratios of stable elements. The AGB stars released O- and C-rich gas with important oxidizing implications to first solar system materials as recently detected in circumstellar environments [3]. REF: [1] Lada C.J. and Lada E.A. 2003. Ann. Rev. A&A. 41: 57; [2] Trigo-Rodriguez J.M. et al. 2009. MAPS 44: 627; [3] Decin L. et al. 2010. Nature 467: 64.

  8. 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

  9. 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.

  10. Post-AGB Stars in Nearby Galaxies as Calibrators for HST

    NASA Technical Reports Server (NTRS)

    Bond, Howard E.

    2003-01-01

    This report summarizes activities carried out with support from the NASA Ultraviolet, Visible, and Gravitational Astrophysics Research and Analysis Program under Grant NAG 5-6821. The Principal Investigator is Howard E. Bond (Space Telescope Science Institute). STScI Postdoctoral Associates Laura K. Fullton (1998), David Alves (1998-2001), and Michael Siegel (2001) were partially supported by this grant. 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 argument is that, in old populations, the stars that are evolving through the PAGB region of the HR diagram arise from only a single main-sequence turnoff mass. In addition, 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, PAGB stars of these spectral types are very easily identified. because of their large Balmer jumps, which are due to their very low surface gravities. Our approach is first to identify PAGB stars in Milky Way globular clusters and in other Local Group galaxies, which are at known distances, and thus to measure accurate absolute magnitudes for the PAGB stars. With this Milky Way and Local Group luminosity calibration, we will then be in a position to find PAGB stars in more distant galaxies from the ground, and ultimately from the Hubble Space Telescope. and thus derive distances. These PAGB stars are, as noted above, the visually brightest members of Population II, and hence will allow distance measurements to galaxies that do not contain Cepheids, such as

  11. Constraining {sup 13}C amounts in AGB stars through isotopic analysis of trace elements in presolar SiC.

    SciTech Connect

    Barzyk, J. G.; Savina, M. R.; Davis, A. M.; Gallino, R.; Gyngard, F.; Amari, S.; Zinner, E.; Pelliln, M. J.; Lewis, R. S.; Clayton, R. N.; Materials Science Division; Univ. Chicago; Chicago Ctr Cosmochem.; Universita di Torino; Washington Univ.

    2007-07-01

    Analyses of the isotopic compositions of multiple elements (Mo, Zr, and Ba) in individual mainstream presolar SiC grains were done by resonant ionization mass spectrometry (RIMS). While most heavy element compositions were consistent with model predictions for the slow neutron capture process (s-process) in low-mass (1.5-3 M{sub {circle_dot}}) asymptotic giant branch stars of solar metallicity when viewed on single-element three-isotope plots, grains with compositions deviating from model predictions were identified on multi-element plots. These grains have compositions that cannot result from any neutron capture process but can be explained by contamination in some elements with solar system material. Previous work in which only one heavy element per grain was examined has been unable to identify contaminated grains. The multi-element analyses of this study detected contaminated grains which were subsequently eliminated from consideration. The uncontaminated grains form a data set with a greatly reduced spread on the three-isotope plots of each element measured, corresponding to a smaller range of {sup 13}C pocket efficiencies in parent AGB stars. Furthermore, due to this reduced spread, the nature of the stellar starting material, previously interpreted as having solar isotopic composition, is uncertain. The constraint on {sup 13}C pocket efficiencies in parent stars of these grains may help uncover the mechanism responsible for formation of {sup 13}C, the primary neutron source for s-process nucleosynthesis in low-mass stars.

  12. The Circumstellar Shell of the Post-Asymptotic Giant Branch Star HD 56126: The 12CN/13CN Isotope Ratio and Fractionation

    NASA Astrophysics Data System (ADS)

    Bakker, Eric J.; Lambert, David L.

    1998-07-01

    We have detected circumstellar absorption lines of the 12CN and 13CN violet and red system in the spectrum of the post-AGB star HD 56126. From a synthetic spectrum analysis, we derive a Doppler broadening parameter of b = 0.51 +/- 0.04 km s-1, 12CN/13CN = 38 +/- 2, and a lower limit of 2000 on 12CN/14CN and 12C14N/12C15N. A simple chemical model has been computed of the circumstellar shell surrounding HD 56126 that takes into account the gas-phase ion-molecule reaction between CN and C+. From this we infer that this reaction leads to isotopic fractionation of CN. Taking into account the isotopic exchange reaction and the observed 12CN/13CN, we find 12C/13C ~ 67 (for Tkin = 25 K). Our analysis suggests that 12CN has a somewhat higher rotational temperature than 13CN: Trot = 11.5 +/- 0.6 and 8.0 +/- 0.6 K, respectively. We identify possible causes for this difference in excitation temperature, among which is the N" dependence of the isotopic exchange reaction.

  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. The AGB star nucleosynthesis in the light of the recent {sup 17}O(p,α){sup 14}N and {sup 18}O(p,α){sup 15}N reaction rate determinations

    SciTech Connect

    Palmerini, S.; Sergi, M. L.; La Cognata, M.; Pizzone, R. G.; Lamia, L.; Spitaleri, C.

    2015-02-24

    Presolar grains form in the cold and dusty envelopes of Asymptotic Giant Branch (AGB) stars. These solides, once that have been ejected by stellar winds, come to us as inclusions in meteorites providing invaluable benchmarks and constraints for our knowledge of low temeperature H-burning in stars. The Trojan Horse Method (THM) has been used to investigate the low-energy cross sections of the {sup 17}O(p,α){sup 14}N and {sup 18}O(p,α){sup 15}N reactions. Moreover, the strength of the 65 keV resonance in the {sup 17}O(p,α){sup 14}N reaction, measured by means of the THM, has been used to renormalize the corresponding resonance strength in the {sup 17}O+p radiative capture channel. The new estimates of the reaction rates have been introduced into calculations of AGB star nucleosynthesis and the results have been compared with geochemical analysis of 'presolar' grains to determine their impact on astrophysical environments.

  15. The effect of the recent 17O(p,α)14N and 18O(p,α)15N fusion cross section measurements in the nucleosynthesis of AGB stars

    NASA Astrophysics Data System (ADS)

    Palmerini, S.; Sergi, M. L.; La Cognata, M.; Lamia, L.; Pizzone, R. G.; Spitaleri, C.

    2015-01-01

    The Trojan Horse Method (THM) has been used to investigate the low-energy cross sections of the 17O(p,α)14N and 18O(p,α)15N fusion reactions and to extract the strengths of the resonances that more contribute to the reaction rates at astrophysical energies. Moreover, the strength of the 65 keV resonance in the 17O(p,α)14N reaction, measured by means of the THM, has been used to renormalize the corresponding resonance strength in the 17O + p radiative capture channel. Since, proton-induced fusion reactions on 17O and 18O belong to the CNO cycle network for H-burning in stars, the new estimates of the cross sections have been introduced into calculations of Asymptotic giant branch (AGB) star nucleosynthesis to determine their impact on astrophysical environments. Results of nucleosynthesis calculations have been compared with geochemical analysis of "presolar" grains. These solids form in the cold and dusty envelopes that surround AGB stars and once that have been ejected by stellar winds, come to us as inclusions in meteorites providing invaluable benchmarks and constraints for our knowledge of fusion reactions in astrophysical environments.

  16. A Luminous Yellow Post-AGB Star in the Galactic Globular Cluster M79

    NASA Astrophysics Data System (ADS)

    Bond, Howard E.; Ciardullo, Robin; Siegel, Michael H.

    2016-02-01

    We report the discovery of a luminous F-type post-asymptotic-giant-branch (PAGB) star in the Galactic globular cluster (GC) M79 (NGC 1904). At visual apparent and absolute magnitudes of V=12.20 and {M}V=-3.46, this “yellow” PAGB star is by a small margin the visually brightest star known in any GC. It was identified using CCD observations in the uBVI photometric system, which is optimized to detect stars with large Balmer discontinuities, indicative of very low surface gravities. Follow-up observations with the SMARTS 1.3 and 1.5 m telescopes show that the star is not variable in light or radial velocity, and that its velocity is consistent with cluster membership. Near- and mid-infrared observations with 2MASS and WISE show no evidence for circumstellar dust. We argue that a sharp upper limit to the luminosity function exists for yellow PAGB stars in old populations, making them excellent candidates for Population II standard candles, which are four magnitudes brighter than RR Lyrae variables. Their luminosities are consistent with the stars being in a PAGB evolutionary phase, with core masses of ˜ 0.53 {M}⊙ . We also detected four very hot stars lying above the horizontal branch (“AGB-manqué” stars); along with the PAGB star, they are the brightest objects in M79 in the near-ultraviolet. In the Appendix, we give periods and light curves for five variables in M79: three RR Lyrae stars, a Type II Cepheid, and a semiregular variable. Based in part on observations with the 1.3 and 1.5 m telescopes operated by the SMARTS Consortium at Cerro Tololo Interamerican Observatory.

  17. Asymptotic Eigenstructures

    NASA Technical Reports Server (NTRS)

    Thompson, P. M.; Stein, G.

    1980-01-01

    The behavior of the closed loop eigenstructure of a linear system with output feedback is analyzed as a single parameter multiplying the feedback gain is varied. An algorithm is presented that computes the asymptotically infinite eigenstructure, and it is shown how a system with high gain, feedback decouples into single input, single output systems. Then a synthesis algorithm is presented which uses full state feedback to achieve a desired asymptotic eigenstructure.

  18. 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

  19. 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

    Context. Asymptotic giant branch (AGB) stars are one of the major sources of dust in the universe. The formation of molecules and dust grains and their subsequent expulsion into the interstellar medium via strong stellar winds is under intense investigation. This is in particular true for oxygen-rich stars, for which the path of dust formation has remained unclear. Aims: We conducted spatially and spectrally resolved mid-infrared multi-epoch interferometric observations to investigate the dust formation process in the extended atmospheres of oxygen-rich AGB stars. Methods: We observed the Mira variable AGB stars S Ori, GX Mon, and R Cnc between February 2006 and March 2009 with the MIDI instrument at the VLT interferometer. We compared the data to radiative transfer models of the dust shells, where the central stellar intensity profiles were described by dust-free dynamic model atmospheres. We used Al2O3 and warm silicate grains, following earlier studies in the literature. Results: Our S Ori and R Cnc data could be well described by an Al2O3 dust shell alone, and our GX Mon data by a mix of an Al2O3 and a silicate shell. The best-fit parameters for S Ori and R Cnc included photospheric angular diameters ΘPhot of 9.7 ± 1.0 mas and 12.3 ± 1.0 mas, optical depths τV(Al2O3) of 1.5 ± 0.5 and 1.35 ± 0.2, and inner radii Rin of 1.9 ± 0.3 RPhot and 2.2 ± 0.3 RPhot, respectively. Best-fit parameters for GX Mon were ΘPhot = 8.7 ± 1.3 mas, τV(Al2O3) = 1.9 ± 0.6, Rin(Al2O3) = 2.1 ± 0.3 RPhot, τV(silicate)= 3.2 ± 0.5, and Rin(silicate)= 4.6 ± 0.2 RPhot. Our data did not show evidence of intra-cycle and cycle-to-cycle variability or of asymmetries within the error-bars and within the limits of our baseline and phase coverage. Conclusions: Our model fits constrain the chemical composition and the inner boundary radii of the dust shells, as well as the photospheric angular diameters. Our interferometric results are consistent with Al2O3 grains condensing close to

  20. 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.

  1. s-processing in AGB stars revisited. I. Does the main component constrain the neutron source in the {sup 13}C pocket?

    SciTech Connect

    Trippella, O.; Busso, M.; Maiorca, E.; Käppeler, F.; Palmerini, S. E-mail: maurizio.busso@fisica.unipg.it

    2014-05-20

    Slow neutron captures at A ≳ 85 are mainly guaranteed by the reaction {sup 13}C(α,n){sup 16}O in asymptotic giant branch (AGB) stars, requiring proton injections from the envelope. These were so far assumed to involve a small mass (≲ 10{sup –3} M {sub ☉}), but models with rotation suggest that in such tiny layers excessive {sup 14}N hampers s-processing. Furthermore, s-element abundances in galaxies require {sup 13}C-rich layers substantially extended in mass (≳ 4 × 10{sup –3} M {sub ☉}). We therefore present new calculations aimed at clarifying those issues and at understanding whether the solar composition helps to constrain the {sup 13}C 'pocket' extension. We show that: (1) mixing 'from bottom to top' (as in magnetic buoyancy or other forced mechanisms) can form a {sup 13}C reservoir substantially larger than assumed so far, covering most of the He-rich layers; (2) on the basis of this idea, stellar models at a fixed metallicity reproduce the main s-component as accurately as before; and (3) they make nuclear contributions from unknown nucleosynthesis processes (LEPP) unnecessary, against common assumptions. These models also avoid problems of mixing at the envelope border and fulfil requirements from C-star luminosities. They yield a large production of nuclei below A = 100, so that {sup 86,} {sup 87}Sr may be fully synthesized by AGB stars, while {sup 88}Sr, {sup 89}Y, and {sup 94}Zr are contributed more efficiently than before. Finally, we suggest tests suitable for providing a final answer regarding the extension of the {sup 13}C pocket.

  2. 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.

  3. Tsunami asymptotics

    NASA Astrophysics Data System (ADS)

    Berry, M. V.

    2005-01-01

    By applying the technique of uniform asymptotic approximation to the oscillatory integrals representing tsunami wave profiles, the form of the travelling wave far from the source is calculated for arbitrary initial disturbances. The approximations reproduce the entire profiles very accurately, from the front to the tail, and their numerical computation is much faster than that of the oscillatory integrals. For one-dimensional propagation, the uniform asymptotics involve Airy functions and their derivatives; for two-dimensional propagation, the uniform asymptotics involve products of these functions. Separate analyses are required when the initial disturbance is specified as surface elevation or surface velocity as functions of position, and when these functions are even or odd. 'There was an awful rainbow once in heaven' (John Keats, 1820)

  4. 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.

  5. 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.

  6. 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.

  7. s-Processing in AGB Stars Revisited. II. Enhanced 13C Production through MHD-induced Mixing

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    Slow neutron captures are responsible for the production of about 50% of elements heavier than iron, mainly occurring during the asymptotic giant branch phase of low-mass stars (1 ≲ M/M⊙ ≲ 3), where the main neutron source is the 13C(α, n)16O reaction. This last reaction is activated from locally produced 13C, formed by partial mixing of hydrogen into the He-rich layers. We present here the first attempt to describe a physical mechanism for the formation of the 13C reservoir, studying the mass circulation induced by magnetic buoyancy without adding new free parameters to those already involved in stellar modeling. Our approach represents the application to the stellar layers relevant for s-processing of recent exact analytical 2D and 3D models for magneto-hydrodynamic processes at the base of convective envelopes in evolved stars in order to promote downflows of envelope material for mass conservation during the occurrence of a dredge-up phenomenon. We find that the proton penetration is characterized by small concentrations, but is extended over a large fractional mass of the He-layers, thus producing 13C reservoirs of several 10-3 M⊙. The ensuing 13C-enriched zone has an almost flat profile, while only a limited production of 14N occurs. In order to verify the effects of our new findings we show how the abundances of the main s-component nuclei can be accounted for in solar proportions and how our large 13C-reservoir allows us to solve a few so far unexplained features in the abundance distribution of post-AGB objects.

  8. Nucleosynthesis in AGB stars: Observation of Mg-25 and Mg-26 in IRC+10216 and possible detection of Al-26

    NASA Technical Reports Server (NTRS)

    Guelin, M.; Forestini, M.; Valiron, P.; Ziurys, L. M.; Anderson, M. A.; Cernicharo, J.; Kahane, C.

    1995-01-01

    We report the detection in the circumstellar envelope IRC+10216 of millimeter lines of the rare isotopomers (25)MgNC and (26)MgNC, as well as of a line at 234433 MHz, which could be the J= 7-6 transition of (26)AlF (an alternate, although less likely identified would be the J= 9-8 transition of NaF). The derived Mg-24:Mg-25:Mg-26 isotopic abundance ratios (78 : 11+/- 1 : 11 +/-1) are consistent with the solar system values (79.0:10.0:11.0), following Anders & Grevesse 1989). According to new calculations of evolutionary models of 3 solar mass and 5 solar mass asymptotic giant branch (AGB) stars, these ratios and the previously measured N, O and Si isotopic ratios imply that the central star had an initial mass 3 solar mass (less than or equal to M(sub *, ini) less than 5 solar mass and has already experienced many 3rd dredge-up events. From this, it can be predicted that the Al-26/Al-27 isotopics ratio lies between 0.01 and 0.08; in fact, the value derived in the case that U234433 arises from (26)AlF is Al-26/Al-27 = 0.04. The identification of the (25)MgNC and (26)MgNC lines was made possible by ab-initio quantum mechanical calculations of the molecule geometrical structure. It was confirmed through millimeter-wave laboratory measurements. The quantum mechanical calculations are briefly described and the laboratory results presented in some detail. The rotation constants B, D, H and the spin-rotation constant gamma of (25)MgNC and (26)MgNC are determined from a fit of laboratory and astronomical data.

  9. Synthetic photometry for carbon-rich giants. II. The effects of pulsation and circumstellar dust

    NASA Astrophysics Data System (ADS)

    Nowotny, W.; Aringer, B.; Höfner, S.; Lederer, M. T.

    2011-05-01

    Context. Red giant stars approaching the end of the evolutionary phase of the asymptotic giant branch (AGB) are, inter alia, characterised by (i) pulsations of the stellar interiors; and (ii) the development of dusty stellar winds. Therefore, such very evolved objects cannot be adequately described with hydrostatic dust-free model atmospheres. Aims: By using self-consistent dynamic model atmospheres which simulate pulsation-enhanced dust-driven winds we studied in detail the influence of the above mentioned two effects on the spectral appearance of long period variables with carbon-rich atmospheric chemistry. While the pulsations lead to large-amplitude photometric variability, the dusty envelopes (resulting from the outflows which contain dust particles composed of amorphous carbon) cause pronounced circumstellar reddening. Methods: Based on one selected dynamical model which is representative of C-type Mira variables with intermediate mass loss rates, we calculated synthetic spectra and photometry for standard broad-band filters (Johnson-Cousins-Glass system) from the visual to the near-infrared. The synthetic photometry was subsequently compared with observational results. Results: Our modelling allows to investigate in detail the substantial effect of circumstellar dust on the resultant photometry. The pronounced absorption of amorphous carbon dust grains (increasing towards shorter wavelengths; Qabs/a ∝ λ - β with β ≈ 1), leads to colour indices which are significantly redder than the corresponding ones based on hydrostatic dust-free models. Only if we account for this circumstellar reddening we get synthetic colours that are comparable to observations of evolved AGB stars. The photometric variations of the dynamical model were compared to observed lightcurves of the C-type Mira RU Vir which appears to be quite similar to the model (although the model is not a dedicated fit). We found good agreement concerning the principal behaviour of the BVRIJHKL

  10. 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.

  11. 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…

  12. 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…

  13. 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…

  14. 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…

  15. 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…

  16. 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:…

  17. Study of the inner dust envelope and stellar photosphere of the AGB star R Doradus using SPHERE/ZIMPOL

    NASA Astrophysics Data System (ADS)

    Khouri, T.; Maercker, M.; Waters, L. B. F. M.; Vlemmings, W. H. T.; Kervella, P.; de Koter, A.; Ginski, C.; De Beck, E.; Decin, L.; Min, M.; Dominik, C.; O'Gorman, E.; Schmid, H.-M.; Lombaert, R.; Lagadec, E.

    2016-06-01

    Context. On the asymptotic giant branch (AGB) low- and intermediate-mass stars eject a large fraction of their envelope, but the mechanism driving these outflows is still poorly understood. For oxygen-rich AGB stars, the wind is thought to be driven by radiation pressure caused by scattering of radiation off dust grains. Aims: We study the photosphere, the warm molecular layer, and the inner wind of the close-by oxygen-rich AGB star R Doradus. We focus on investigating the spatial distribution of the dust grains that scatter light and whether these grains can be responsible for driving the outflow of this star. Methods: We use high-angular-resolution images obtained with SPHERE/ZIMPOL to study R Dor and its inner envelope in a novel way. We present observations in filters V, cntHα, and cnt820 and investigate the surface brightness distribution of the star and of the polarised light produced in the inner envelope. Thanks to second-epoch observations in cntHα, we are able to see variability on the stellar photosphere. We study the polarised-light data using a continuum-radiative-transfer code that accounts for direction-dependent scattering of photons off dust grains. Results: We find that in the first epoch the surface brightness of R Dor is asymmetric in V and cntHα, the filters where molecular opacity is stronger, while in cnt820 the surface brightness is closer to being axisymmetric. The second-epoch observations in cntHα show that the morphology of R Dor has changed completely in a timespan of 48 days to a more axisymmetric and compact configuration. This variable morphology is probably linked to changes in the opacity provided by TiO molecules in the extended atmosphere. The observations show polarised light coming from a region around the central star. The inner radius of the region from where polarised light is seen varies only by a small amount with azimuth. The value of the polarised intensity, however, varies by between a factor of 2.3 and 3.7 with

  18. 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

  19. THE CH(G) INDEX AS A NEW CRITERION FOR SELECTING RED GIANT STARS

    SciTech Connect

    Chen, Y. Q.; Zhao, G.; Carrell, K.; Zhao, J. K.; Tan, K. F.

    2013-03-10

    We have measured the CH G band (CH(G)) index for evolved stars in the globular cluster M3 based on the Sloan Digital Sky Survey (SDSS) spectroscopic survey. It is found that there is a useful way to select red giant branch (RGB) stars from the contamination of other evolved stars such as asymptotic giant branch (AGB) and red horizontal branch (RHB) stars by using the CH(G) index versus (g - r){sub 0} diagram if the metallicity is known from the spectra. When this diagram is applied to field giant stars with similar metallicity, we establish a calibration of CH(G) = 1.625(g - r){sub 0} - 1.174(g - r){sup 2}{sub 0} - 0.934. This method is confirmed by stars with [Fe/H] {approx} -2.3 where spectra of member stars in globular clusters M15 and M92 are available in the SDSS database. We thus extend this kind of calibration to every individual metallicity bin ranging from [Fe/H] {approx} -3.0 to [Fe/H] {approx} 0.0 by using field red giant stars with 0.4 {<=} (g - r){sub 0} {<=} 1.0. The metallicity-dependent calibrations give CH(G) = 1.625(g - r){sub 0} - 1.174(g - r){sup 2}{sub 0} + 0.060[Fe/H] - 0.830 for -3.0 < [Fe/H] {<=} -1.2 and CH(G) = 0.953(g - r){sub 0} - 0.655(g - r){sup 2}{sub 0} + 0.060[Fe/H] - 0.650 for -1.2 < [Fe/H] < 0.0. The calibrations are valid for the SDSS spectroscopic data set, and they cannot be applied blindly to other data sets. With the two calibrations, a significant number of the contaminating stars (AGB and RHB stars) were excluded and thus a clear sample of red giant stars is obtained by selecting stars within {+-}0.05 mag of the calibration. The sample is published online and it is expected that this large and clean sample of RGB stars will provide new information on the formation and evolution of the Galaxy.

  20. 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

  1. Giant Magnons Meet Giant Gravitons

    SciTech Connect

    Hofman, Diego M.

    2008-07-28

    We study the worldsheet reflection matrix of a string attached to a D-brane in AdS{sub 5}xS{sup 5}. The D-brane corresponds to a maximal giant graviton that wraps an S{sup 3} inside S{sup 5}. In the gauge theory, the open string is described by a spin chain with boundaries. We focus on open strings with a large SO(6) charge and define an asymptotic boundary reflection matrix. Using the symmetries of the problem, we review the computation of the boundary reflection matrix, up to a phase. We also discuss weak and strong coupling computations where we obtain the overall phase factor and test our exact results.

  2. Chemical abundance study of two strongly s-process enriched post-AGB stars in the LMC: J051213.81-693537.1 and J051848.86-700246.9

    NASA Astrophysics Data System (ADS)

    De Smedt, K.; Van Winckel, H.; Kamath, D.; Wood, P. R.

    2015-11-01

    Context. This paper is part of a larger project in which we systematically study the chemical abundances of extra-galactic post-asymptotic giant branch (post-AGB) stars. The aim of our programme is to derive chemical abundances of stars covering a large range in luminosity and metallicity with the ultimate goal of testing, constraining, and improving our knowledge of the poorly understood AGB phase, especially the third dredge-up mixing processes and associated s-process nucleosynthesis. Aims: Post-AGB photospheres are dominated by atomic lines and indicate the effects of internal chemical enrichment processes over the entire stellar lifetime. In this paper, we study two carefully selected post-AGB stars: J051213.81-693537.1 and J051848.86-700246.9 in the Large Magellanic Cloud (LMC). Both objects show signs of s-process enhancement. The combination of favourable atmospheric parameters for detailed abundance studies and their known distances (and hence luminosities and initial masses) make these objects ideal probes of the AGB third dredge-up and s-process nucleosynthesis in that they provide observational constraints for theoretical AGB models. Methods: We use high-resolution optical UVES spectra to determine accurate stellar parameters and subsequently perform detailed elemental abundance studies of post-AGB stars. Additionally, we use available photometric data covering optical and IR bands to construct spectral energy distributions for reddening and luminosity determinations. We then estimate initial masses from theoretical post-AGB tracks. Results: We obtained accurate atmospheric parameters for J051213.81-693537.1 (Teff = 5875 ± 125 K, log g = 1.00 ± 0.25 dex, [Fe/H] = -0.56 ± 0.16 dex) and J051848.86-700246.9 (Teff = 6000 ± 125 K, log g = 0.50 ± 0.25 dex, [Fe/H] = -1.06 ± 0.17 dex). Both stars show extreme s-process enrichment associated with relatively low C/O ratios of 1.26 ± 0.40 and 1.29 ± 0.30 for J051213-693537.1 and J051848

  3. The Carbon-13 Pockets in AGB Stars and Their Fingerprints in Mainstream SiC Grains

    NASA Astrophysics Data System (ADS)

    Liu, N.; Davis, A. M.; Gallino, R.; Savina, M. R.; Bisterzo, S.; Gyngard, F.; Dauphas, N.; Pellin, M. J.

    2014-09-01

    Strontium, Zr, and Ba isotopic compositions of mainstream presolar SiC grains are used to constrain the concentration and distribution of carbon-13, the main neutron source for the s-process, in the intershell region of asymptotic giant branch stars.

  4. 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.

  5. Cool Giant Atlases in the CRIRES-POP Library

    NASA Astrophysics Data System (ADS)

    Nicholls, C.; Lebzelter, T.; Crires-Pop Team

    2015-08-01

    The CRIRES-POP project will provide a public database of high resolution, high signal/noise near-infrared spectra of stars spanning the HR diagram. A relevant part of this library for the AGB community will be high quality reference spectra of several cool evolved giants.

  6. Investigation of Faint Galactic Carbon Stars from the First Byurakan Spectral sky Survey. Optical Variability. I. N-Type AGB Carbon Stars. K-band Absolute Magnitudes and Distances

    NASA Astrophysics Data System (ADS)

    Gigoyan, K. S.; Sarkissian, A.; Russeil, D.; Mauron, N.; Kostandyan, G.; Vartanian, R.; Abrahamyan, H. V.; Paronyan, G. M.

    2014-12-01

    The goal of this paper is to present an optical variability study of the comparatively faint carbon (C) stars which have been discovered by searching the First Byurakan Survey (FBS) low-resolution (lr) spectral plates at high Galactic latitudes using recent wide-area variability databases. The light curves from the Catalina Sky Survey (CSS) and Northern Sky Variability Survey (NSVS) databases were exploited to study theit variability nature. In this paper, first in this series, the variability classes are presented for 54 N-type Asymptotic Giant Branch (AGB) C stars. One finds that 9 stars belongs to the group of Mira-type, 43 are Semi-Regular (SR), and 2 stars are Irregular (Irr)-type variables. The variability types of 27 objects has been established for the first time. K-band absolute magnitudes, distances, and height from the Galactic plane were estimated for all of them. We aim to better understand the nature of the selected C stars through spectroscopy, 2MASS photometric colors, and variability data. Most of the tools used in this study are developed within the framework of the Astronomical Virtual Observatory.

  7. 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

  8. 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…

  9. THE RGB AND AGB STAR NUCLEOSYNTHESIS IN LIGHT OF THE RECENT {sup 17}O(p, {alpha}){sup 14}N AND {sup 18}O(p, {alpha}){sup 15}N REACTION-RATE DETERMINATIONS

    SciTech Connect

    Palmerini, S.; Sergi, M. L.; La Cognata, M.; Pizzone, R. G.; Spitaleri, C.; Lamia, L.

    2013-02-20

    In recent years, the Trojan Horse Method (THM) has been used to investigate the low-energy cross sections of proton-induced reactions on A = 17 and A = 18 oxygen isotopes, overcoming extrapolation procedures and enhancement effects due to electron screening. In particular, the strengths of the 20 keV and 65 keV resonances in the {sup 18}O(p, {alpha}){sup 15}N and {sup 17}O(p, {alpha}){sup 14}N reactions, respectively, have been extracted, as well as the contribution of the tail of the broad 656 keV resonance in the {sup 18}O(p, {alpha}){sup 15}N reaction inside the Gamow window. The strength of the 65 keV resonance in the {sup 17}O(p, {alpha}){sup 14}N reaction, measured by means of the THM, has been used to renormalize the corresponding resonance strength in the {sup 17}O + p radiative capture channel. As a result, more accurate reaction rates for the {sup 18}O(p, {alpha}){sup 15}N, {sup 17}O(p, {alpha}){sup 14}N, and {sup 17}O(p, {gamma}){sup 18}F processes have been deduced, devoid of systematic errors due to extrapolation or the electron screening effect. Such rates have been introduced into state-of-the-art red giant branch and asymptotic giant branch (AGB) models for proton-capture nucleosynthesis coupled with extra-mixing episodes. The predicted abundances have been compared with isotopic compositions provided by geochemical analysis of presolar grains. As a result, an improved agreement is found between the models and the isotopic mix of oxide grains of AGB origins, whose composition is the signature of low-temperature proton-capture nucleosynthesis. The low {sup 14}N/{sup 15}N found in SiC grains cannot be explained by the revised nuclear reaction rates and remains a serious problem that has not been satisfactorily addressed.

  10. On Potassium and Other Abundance Anomalies of Red Giants in NGC 2419

    NASA Astrophysics Data System (ADS)

    Iliadis, C.; Karakas, A. I.; Prantzos, N.; Lattanzio, J. C.; Doherty, C. L.

    2016-02-01

    Globular clusters are of paramount importance for testing theories of stellar evolution and early galaxy formation. Strong evidence for multiple populations of stars in globular clusters derives from observed abundance anomalies. A puzzling example is the recently detected Mg-K anticorrelation in NGC 2419. We perform Monte Carlo nuclear reaction network calculations to constrain the temperature-density conditions that gave rise to the elemental abundances observed in this elusive cluster. We find a correlation between stellar temperature and density values that provide a satisfactory match between simulated and observed abundances in NGC 2419 for all relevant elements (Mg, Si, K, Ca, Sc, Ti, and V). Except at the highest densities (ρ ≳ 108 g cm-3), the acceptable conditions range from ≈100 MK at ≈108 g cm-3 to ≈200 MK at ≈10-4 g cm-3. This result accounts for uncertainties in nuclear reaction rates and variations in the assumed initial composition. We review hydrogen-burning sites and find that low-mass stars, asymptotic giant branch (AGB) stars, massive stars, or supermassive stars cannot account for the observed abundance anomalies in NGC 2419. Super-AGB stars could be viable candidates for the polluter stars if stellar model parameters can be fine-tuned to produce higher temperatures. Novae, involving either CO or ONe white dwarfs, could be interesting polluter candidates, but a current lack of low-metallicity nova models precludes firmer conclusions. We also discuss whether additional constraints for the first-generation polluters can be obtained by future measurements of oxygen, or by evolving models of second-generation low-mass stars with a non-canonical initial composition.

  11. 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

  12. 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.

  13. 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.

  14. Asymptotes in Polar Coordinates.

    ERIC Educational Resources Information Center

    Fay, Temple H.

    1986-01-01

    An old way to determine asymptotes for curves described in polar coordinates is presented. Practice in solving trigonometric equations, in differentiation, and in calculating limits is involved. (MNS)

  15. The distance to the giant elliptical galaxy NGC 5128

    NASA Astrophysics Data System (ADS)

    Rejkuba, M.

    2004-01-01

    The distance to NGC 5128, the central galaxy of the Centaurus group and the nearest giant elliptical to us, has been determined using two independent distance indicators: the Mira period-luminosity (PL) relation and the luminosity of the tip of the red giant branch (RGB). The data were taken at two different locations in the halo of NGC 5128 with the ISAAC near-IR array on ESO VLT. From more than 20 hours of observations with ISAAC a very deep Ks-band luminosity function was constructed. The tip of the RGB is detected at Ks=21.24 ± 0.05 mag. Using an empirical calibration of the K-band RGB tip magnitude, and assuming a mean metallicity of [M/ H]=-0.4 dex and reddening of E(B-V)=0.11, a distance modulus of NGC 5128 of (m-M)0=27.87 ± 0.16 was derived. The comparison of the H-band RGB tip magnitude in NGC 5128 and the Galactic Bulge implies a distance modulus of NGC 5128 of (m-M)0=27.9 ± 0.2 in good agreement with the K-band RGB tip measurement. The inner halo field has larger photometric errors, brighter completeness limits and a larger number of blends. Thus the RGB tip feature is not as sharp as in the outer halo field. The population of stars above the tip of the RGB amounts to 2176 stars in the outer halo field (Field 1) and 6072 stars in the inner halo field (Field 2). The large majority of these sources belong to the asymptotic giant branch (AGB) population in NGC 5128 with numerous long period variables. Mira variables were used to determine the distance of NGC 5128 from a period-luminosity relation calibrated using the Hipparcos parallaxes and LMC Mira period-luminosity relation in the K-band. This is the first Mira period-luminosity relation outside the Local Group. A distance modulus of 27.96 ± 0.11 was derived, adopting the LMC distance modulus of 18.50 ± 0.04. The mean of the two methods yields a distance modulus to NGC 5128 of 27.92 ± 0.19 corresponding to D=3.84 ± 0.35 Mpc. Based on observations collected at the European Southern Observatory

  16. 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.

  17. The Circumstellar Shell of the Post-Asymptotic Giant Branch Star HD 56126: 12C12C/12C13C Isotope Ratio and 12C16O Column Density

    NASA Astrophysics Data System (ADS)

    Bakker, Eric J.; Lambert, David L.

    1998-11-01

    We have made the first detection of circumstellar absorption lines of the 12C13C A 1Πu-X 1Σ+g (Phillips) system 1-0 band and the 12C16O X 1Σ+ first-overtone 2-0 band in the spectrum of the post-AGB star HD 56126 (IRAS 07134+1005). All current detections of circumstellar molecular absorption lines toward HD 56126 (12C2, 12C13C, 12C14N, 13C14N, and 12C16O) yield the same heliocentric velocity of VCSE = 77.6 +/- 0.4 km s-1. The 12C2, 12C13C, and 12C16O lines give rotational temperatures and integrated column densities of Trot = 328 +/- 37 K, log Nint = 15.34 +/- 0.10 cm-2, Trot = 256 +/- 30 K, log Nint = 13.79 +/- 0.12 cm-2, and Trot = 51 +/- 37 K, log Nint = 18.12 +/- 0.13 cm-2, respectively. The rotational temperatures are lower for molecules with a higher permanent dipole moment. Derived relative column densities ratios are 12C2/12C13C = 36 +/- 13 and 12C16O/(12C2 + 12C13C) = 606 +/- 230. Combined with data from a previous paper, we find relative column densities of 12C16O/(12C14N + 13C14N) = 475 +/- 175 and 12C14N/13C14N = 38 +/- 2. Under chemical equilibrium conditions, 12C13C is formed twice as easily as 12C2. The isotopic exchange reaction for 12C2 is too slow to significantly alter the 12C2/12C13C ratio, and the 12C2 to 12C13C ratio is a good measure of half the carbon isotope ratio: 12C/13C = 2 × 12C2/12C13C = 72 +/- 26. This is in agreement with our prediction that the isotopic exchange reaction for 12C14N is efficient and our observation in Paper III of 12C14N/13C14N = 38 +/- 2. A fit of the C2 excitation model of van Dishoeck & Black to the relative population distribution of C2 yields nc σ/I = 3.3 +/- 1.0 × 10-14. At r ~= 1016 cm, this translates into nc = 1.7 × 107 cm-3 and Ṁ~=2.5×10-4 M⊙ yr-1.

  18. Characteristics of convection and overshooting in RGB and AGB stars

    NASA Astrophysics Data System (ADS)

    Lai, Xiang-Jun; Li, Yan

    2011-10-01

    Based on the turbulent convection model (TCM) of Li & Yang, we have studied the characteristics of turbulent convection in the envelopes of 2 and 5Modot stars at the red giant branch and asymptotic giant branch phases. The TCM has been successfully applied over the entire convective envelopes, including the convective unstable zone and the overshooting regions. We find that the convective motions become progressively stronger when the stellar models are located farther up along the Hayashi line. In the convective unstable zone, we find that the turbulent correlations are proportional to functions of a common factor (∇ - ∇ad)T¯, which explains similar distributions in those correlations. For the TCM we find that if the obtained stellar temperature structure is close to that of the mixing length theory (MLT), the convective motion will have a much larger velocity and thus be more violent. However, if the turbulent velocity is adjusted to be close to that of the MLT, the superadiabatic convection zone would be much more extended inward, which would lead to a lower effective temperature of the stellar model. For the overshooting distance, we find that the e-folding lengths of the turbulent kinetic energy k in both the top and bottom overshooting regions decrease as the stellar model is progressively located farther up along the Hayashi line, but both the extents of the decrease are not obvious. The overshooting distances of the turbulent correlation are almost the same for the different stellar models with the same set of TCM parameters. For the decay modes of the kinetic energy k, we find that they are very similar for different stellar models based on the same set of TCM parameters, and there is a nearly linear relationship between lg k and ln P for different stellar models. When Cs or α increases while the other parameters are fixed, the obtained linearly decaying distance will become longer.

  19. Asymptotic entropy bounds

    NASA Astrophysics Data System (ADS)

    Bousso, Raphael

    2016-07-01

    We show that known entropy bounds constrain the information carried off by radiation to null infinity. We consider distant, planar null hypersurfaces in asymptotically flat spacetime. Their focusing and area loss can be computed perturbatively on a Minkowski background, yielding entropy bounds in terms of the energy flux of the outgoing radiation. In the asymptotic limit, we obtain boundary versions of the quantum null energy condition, of the generalized Second Law, and of the quantum Bousso bound.

  20. Synthetic photometry for carbon-rich giants. IV. An extensive grid of dynamic atmosphere and wind models

    NASA Astrophysics Data System (ADS)

    Eriksson, K.; Nowotny, W.; Höfner, S.; Aringer, B.; Wachter, A.

    2014-06-01

    Context. The evolution and spectral properties of stars on the asymptotic giant branch (AGB) are significantly affected by mass loss through dusty stellar winds. Dynamic atmosphere and wind models are an essential tool for studying these evolved stars, both individually and as members of stellar populations, to understand their contribution to the integrated light and chemical evolution of galaxies. Aims: This paper is part of a series with the purpose of testing state-of-the-art atmosphere and wind models of C-type AGB stars against observations, and making them available to the community for use in various theoretical and observational studies. Methods: We have computed low-resolution spectra and photometry (in the wavelength range 0.35-25 μm) for a grid of 540 dynamic models with stellar parameters typical of solar-metallicity C-rich AGB stars and with a range of pulsation amplitudes. The models cover the dynamic atmosphere and dusty outflow (if present), assuming spherical symmetry, and taking opacities of gas-phase species and dust grains consistently into account. To characterize the time-dependent dynamic and photometric behaviour of the models in a concise way we defined a number of classes for models with and without winds. Results: Comparisons with observed data in general show a quite satisfactory agreement for example regarding mass-loss rates vs. (J - K) colours or K magnitudes vs. (J - K) colours. Some exceptions from the good overall agreement, however, are found and attributed to the range of input parameters (e.g. relatively high carbon excesses) or intrinsic model assumptions (e.g. small particle limit for grain opacities). Conclusions: While current results indicate that some changes in model assumptions and parameter ranges should be made in the future to bring certain synthetic observables into better agreement with observations, it seems unlikely that these pending improvements will significantly affect the mass-loss rates of the models

  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. 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.

  3. 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.

  4. 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.

  5. 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).

  6. 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…

  7. 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.

  8. Dust clouds around red giant stars - Evidence of sublimating comet disks?

    NASA Astrophysics Data System (ADS)

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

    1989-09-01

    The dust production by disk comets around intermediate mass stars evolving into red giants is studied, focusing on AGB supergiants. The model of Iben and Renzini (1983) is used to study the observed dust mass loss for AGB stars. An expression is obtained for the comet disk net dust production rate and values of the radius and black body temperature corresponding to peak sublimation are calculated for a range of stellar masses. Also, the fractional amount of dust released from a cometesimal disk during a classical nova outburst is estimated.

  9. Asymptotics for spherical needlets

    NASA Astrophysics Data System (ADS)

    Baldi, P.; Kerkyacharian, G.; Marinucci, D.; Picard, D.

    We investigate invariant random fields on the sphere using a new type of spherical wavelets, called needlets. These are compactly supported in frequency and enjoy excellent localization properties in real space, with quasi-exponentially decaying tails. We show that, for random fields on the sphere, the needlet coefficients are asymptotically uncorrelated for any fixed angular distance. This property is used to derive CLT and functional CLT convergence results for polynomial functionals of the needlet coefficients: here the asymptotic theory is considered in the high-frequency sense. Our proposals emerge from strong empirical motivations, especially in connection with the analysis of cosmological data sets.

  10. Asymptotically safe Higgs inflation

    SciTech Connect

    Xianyu, Zhong-Zhi; He, Hong-Jian E-mail: hjhe@tsinghua.edu.cn

    2014-10-01

    We construct a new inflation model in which the standard model Higgs boson couples minimally to gravity and acts as the inflaton. Our construction of Higgs inflation incorporates the standard model with Einstein gravity which exhibits asymptotic safety in the ultraviolet region. The slow roll condition is satisfied at large field value due to the asymptotically safe behavior of Higgs self-coupling at high energies. We find that this minimal construction is highly predictive, and is consistent with both cosmological observations and collider experiments.

  11. On the interior properties of red giants

    NASA Astrophysics Data System (ADS)

    Iben, I., Jr.

    The interior evolution of red giants is focused on, the major emphasis being on the evolution of stars during the double shell-burning stage. The evolutionary course during the first and second ascent up the red giant branch of the H-R diagram are discussed for stars that vary with respect to certain critical masses, and the thermal pulse phase is also treated. Core, envelope, and surface phenomena are explained along with the process of development into white dwarfs or supernovas. The interplay of internal forces caused by various fuel-burning processes, electron-degeneracy pressure, and gravity are detailed, and phenomena such as core dredge-up, relaxed oscillations, and AGB stars are explained. Numbers are given for the properties of H-burning and convective shells, and detailed comparisons with observations are made.

  12. An asymptotical machine

    NASA Astrophysics Data System (ADS)

    Cristallini, Achille

    2016-07-01

    A new and intriguing machine may be obtained replacing the moving pulley of a gun tackle with a fixed point in the rope. Its most important feature is the asymptotic efficiency. Here we obtain a satisfactory description of this machine by means of vector calculus and elementary trigonometry. The mathematical model has been compared with experimental data and briefly discussed.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. Asymptotic symmetries from finite boxes

    NASA Astrophysics Data System (ADS)

    Andrade, Tomás; Marolf, Donald

    2016-01-01

    It is natural to regulate an infinite-sized system by imposing a boundary condition at finite distance, placing the system in a 'box.' This breaks symmetries, though the breaking is small when the box is large. One should thus be able to obtain the asymptotic symmetries of the infinite system by studying regulated systems. We provide concrete examples in the context of Einstein-Hilbert gravity (with negative or zero cosmological constant) by showing in 4 or more dimensions how the anti-de Sitter and Poincaré asymptotic symmetries can be extracted from gravity in a spherical box with Dirichlet boundary conditions. In 2 + 1 dimensions we obtain the full double-Virasoro algebra of asymptotic symmetries for AdS3 and, correspondingly, the full Bondi-Metzner-Sachs (BMS) algebra for asymptotically flat space. In higher dimensions, a related approach may continue to be useful for constructing a good asymptotically flat phase space with BMS asymptotic symmetries.

  20. The astrosphere of the asymptotic giant branch star CIT 6

    SciTech Connect

    Sahai, Raghvendra; Mack-Crane, Galen P.

    2014-10-01

    We have discovered two extended half-ring structures in a far-ultraviolet image taken with the GALEX satellite of the well-known mass-losing carbon star CIT 6 (RW LMi). The northern (southern) ring is brighter (fainter) with a diameter of ∼15' (∼18'). These structures most likely represent the astrosphere resulting from the shock interaction of CIT 6's molecular wind with the warm interstellar medium (ISM), as it moves through the latter. These data provide a direct estimate of the size of CIT 6's circumstellar envelope that is a factor ∼20 larger than previous estimates based on CO millimeter-wave line data. We find that CIT 6 has been undergoing heavy mass-loss for at least 93,000 yr and the total envelope mass is 0.29 M {sub ☉} or larger, assuming a constant mass-loss rate of 3.2 × 10{sup –6} M {sub ☉} yr{sup –1}. Assuming that the shock front has reached a steady state and CIT 6's motion relative to the ISM is in the sky plane, we measure the termination-shock standoff distance directly from the image and find that CIT 6 is moving at a speed of about ≳39 (0.17 cm{sup –3}/n {sub ISM}){sup 1/2} km s{sup –1} through the ISM around it. However, comparisons with published numerical simulations and analytical modeling shows that CIT 6's forward shock (the northern ring) departs from the parabolic shape expected in steady state. We discuss several possible explanations for this departureþ.

  1. 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.

  2. 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.

  3. 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…

  4. The dynamic atmospheres of red giant stars. Spectral synthesis in high resolution

    NASA Astrophysics Data System (ADS)

    Nowotny, W.

    2005-11-01

    Light is the only source of information we have to study distant stars. Our knowledge about the state of the matter inside stars has been gathered by analysing star light (photometry, spectroscopy, interferometry, polarimetry, etc.). Of central importance in this context are stellar atmospheres, which are the transition regions from the optically thick stellar interiors where the electromagnetic radiation is generated to the optically thin outer layers from where the photons can leave the star. However, the atmosphere of a star is not only the region where most of the observable radiation is emitted or in other words the layers which are "visible from outside". The atmosphere also leaves an imprint on the stellar spectrum as the radiation passes through, most of the line spectrum is formed there. Thus, the light serves as a probe for the physical processes within stellar atmospheres, especially spectroscopy is one of the major tools in stellar astrophysics. Applying the underlying physical principles in numerical simulations (model atmospheres, synthetic spectra) is the second -- complementary and necessary -- step towards a deeper understanding of stellar atmospheres and for deriving stellar parameters (e.g. T_eff, L, log g, chemical composition) of observed objects. This thesis is dedicated to the outer layers of Asymptotic Giant Branch (AGB) stars, which have rather remarkable properties compared to atmospheres of most other types of stars. AGB stars represent low- to intermediate mass stars at a late stage of their evolution. Forming a sub-group among all red giants, they exhibit large extensions, low effective temperatures and high luminosities. The evolutionary phase of the AGB -- complex but decisive for stellar evolution -- is characterised by several important phenomena as for example nucleo-synthesis in explosively burning shells (thermal pulses), convective processes (dredge up), large-amplitude pulsations with long periods or a pronounced mass loss. Red

  5. Dynamics of Dollard asymptotic variables. Asymptotic fields in Coulomb scattering

    NASA Astrophysics Data System (ADS)

    Morchio, G.; Strocchi, F.

    2016-03-01

    Generalizing Dollard’s strategy, we investigate the structure of the scattering theory associated to any large time reference dynamics UD(t) allowing for the existence of Møller operators. We show that (for each scattering channel) UD(t) uniquely identifies, for t →±∞, asymptotic dynamics U±(t); they are unitary groups acting on the scattering spaces, satisfy the Møller interpolation formulas and are interpolated by the S-matrix. In view of the application to field theory models, we extend the result to the adiabatic procedure. In the Heisenberg picture, asymptotic variables are obtained as LSZ-like limits of Heisenberg variables; their time evolution is induced by U±(t), which replace the usual free asymptotic dynamics. On the asymptotic states, (for each channel) the Hamiltonian can by written in terms of the asymptotic variables as H = H±(qout/in,pout/in), H±(q,p) the generator of the asymptotic dynamics. As an application, we obtain the asymptotic fields ψout/in in repulsive Coulomb scattering by an LSZ modified formula; in this case, U±(t) = U0(t), so that ψout/in are free canonical fields and H = H0(ψout/in).

  6. A molecular line survey of a sample of AGB stars and planetary nebulae

    NASA Astrophysics Data System (ADS)

    Smith, C. L.; Zijlstra, A. A.; Fuller, G. A.

    2015-11-01

    A millimeter molecular line survey of three carbon-rich asymptotic giant branch stars and two oxygen-rich planetary nebulae has been carried out over the frequency range 80.5-115.5 GHz. 68 different transitions were detected in the data from 27 different molecular species. The hyperfine structure of C2H and C13CH has been fitted to constrain the optical depth of their transitions. All other transitions have been constrained on the basis of their line profile shapes. Rotation temperatures and column densities have been calculated for all possible species, with adaptations to the methods applied in order to account for the hyperfine structure of various transitions. From the column densities, carbon, silicon and sulphur isotopic ratios have been determined. The results corroborate IRAS 15194-5115 as a J-type star, whilst excluding IRAS 15082-4808 and IRAS 07454-7112 as such.

  7. An edge-on translucent dust disk around the nearest AGB star, L2 Puppis. VLT/NACO spectro-imaging from 1.04 to 4.05 μm and VLTI interferometry

    NASA Astrophysics Data System (ADS)

    Kervella, P.; Montargès, M.; Ridgway, S. T.; Perrin, G.; Chesneau, O.; Lacour, S.; Chiavassa, A.; Haubois, X.; Gallenne, A.

    2014-04-01

    As the nearest known AGB star (d = 64 pc) and one of the brightest (mK ≈ -2), L2 Pup is a particularly interesting benchmark object to monitor the final stages of stellar evolution. We report new serendipitous imaging observations of this star with the VLT/NACO adaptive optics system in twelve narrow-band filters covering the 1.0-4.0 μm wavelength range. These diffraction-limited images reveal an extended circumstellar dust lane in front of the star that exhibits a high opacity in the J band and becomes translucent in the H and K bands. In the L band, extended thermal emission from the dust is detected. We reproduced these observations using Monte Carlo radiative transfer modeling of a dust disk with the RADMC-3D code. We also present new interferometric observations with the VLTI/VINCI and MIDI instruments. We measured in the K band an upper limit to the limb-darkened angular diameter of θLD = 17.9 ± 1.6 mas, converting to a maximum linear radius of R = 123 ± 14 R⊙. Considering the geometry of the extended K band emission in the NACO images, this upper limit is probably close to the actual angular diameter of the star. The position of L2 Pup in the Hertzsprung-Russell diagram indicates that this star has a mass of about 2 M⊙ and is probably experiencing an early stage of the asymptotic giant branch. We did not detect any stellar companion of L2 Pup in our adaptive optics and interferometric observations, and we attribute its apparent astrometric wobble in the Hipparcos data to variable lighting effects on its circumstellar material. However, we do not exclude the presence of a binary companion, because the large loop structure extending to more than 10 AU to the northeast of the disk in our L-band images may be the result of interaction between the stellar wind of L2 Pup and a hidden secondary object. The geometric configuration that we propose, with a large dust disk seen almost edge-on, appears particularly favorable to test and develop our

  8. Asymptotic entropic uncertainty relations

    NASA Astrophysics Data System (ADS)

    Adamczak, Radosław; Latała, Rafał; Puchała, Zbigniew; Życzkowski, Karol

    2016-03-01

    We analyze entropic uncertainty relations for two orthogonal measurements on a N-dimensional Hilbert space, performed in two generic bases. It is assumed that the unitary matrix U relating both bases is distributed according to the Haar measure on the unitary group. We provide lower bounds on the average Shannon entropy of probability distributions related to both measurements. The bounds are stronger than those obtained with use of the entropic uncertainty relation by Maassen and Uffink, and they are optimal up to additive constants. We also analyze the case of a large number of measurements and obtain strong entropic uncertainty relations, which hold with high probability with respect to the random choice of bases. The lower bounds we obtain are optimal up to additive constants and allow us to prove a conjecture by Wehner and Winter on the asymptotic behavior of constants in entropic uncertainty relations as the dimension tends to infinity. As a tool we develop estimates on the maximum operator norm of a submatrix of a fixed size of a random unitary matrix distributed according to the Haar measure, which are of independent interest.

  9. Giant Axonal Neuropathy

    MedlinePlus

    ... Diversity Find People About NINDS NINDS Giant Axonal Neuropathy Information Page Table of Contents (click to jump ... done? Clinical Trials Organizations What is Giant Axonal Neuropathy? Giant axonal neuropathy (GAN) is a rare inherited ...

  10. Asymptotic Parachute Performance Sensitivity

    NASA Technical Reports Server (NTRS)

    Way, David W.; Powell, Richard W.; Chen, Allen; Steltzner, Adam D.

    2006-01-01

    In 2010, the Mars Science Laboratory mission will pioneer the next generation of robotic Entry, Descent, and Landing systems by delivering the largest and most capable rover to date to the surface of Mars. In addition to landing more mass than any other mission to Mars, Mars Science Laboratory will also provide scientists with unprecedented access to regions of Mars that have been previously unreachable. By providing an Entry, Descent, and Landing system capable of landing at altitudes as high as 2 km above the reference gravitational equipotential surface, or areoid, as defined by the Mars Orbiting Laser Altimeter program, Mars Science Laboratory will demonstrate sufficient performance to land on 83% of the planet s surface. By contrast, the highest altitude landing to date on Mars has been the Mars Exploration Rover at 1.3 km below the areoid. The coupling of this improved altitude performance with latitude limits as large as 60 degrees off of the equator and a precise delivery to within 10 km of a surface target, will allow the science community to select the Mars Science Laboratory landing site from thousands of scientifically interesting possibilities. In meeting these requirements, Mars Science Laboratory is extending the limits of the Entry, Descent, and Landing technologies qualified by the Mars Viking, Mars Pathfinder, and Mars Exploration Rover missions. Specifically, the drag deceleration provided by a Viking-heritage 16.15 m supersonic Disk-Gap-Band parachute in the thin atmosphere of Mars is insufficient, at the altitudes and ballistic coefficients under consideration by the Mars Science Laboratory project, to maintain necessary altitude performance and timeline margin. This paper defines and discusses the asymptotic parachute performance observed in Monte Carlo simulation and performance analysis and its effect on the Mars Science Laboratory Entry, Descent, and Landing architecture.

  11. Exponential tilting in Bayesian asymptotics

    PubMed Central

    Kharroubi, S. A.; Sweeting, T. J.

    2016-01-01

    We use exponential tilting to obtain versions of asymptotic formulae for Bayesian computation that do not involve conditional maxima of the likelihood function, yielding a more stable computational procedure and significantly reducing computational time. In particular we present an alternative version of the Laplace approximation for a marginal posterior density. Implementation of the asymptotic formulae and a modified signed root based importance sampler are illustrated with an example. PMID:27279661

  12. Asymptotic dynamics of monopole walls

    NASA Astrophysics Data System (ADS)

    Cross, R.

    2015-08-01

    We determine the asymptotic dynamics of the U(N) doubly periodic BPS monopole in Yang-Mills-Higgs theory, called a monopole wall, by exploring its Higgs curve using the Newton polytope and amoeba. In particular, we show that the monopole wall splits into subwalls when any of its moduli become large. The long-distance gauge and Higgs field interactions of these subwalls are Abelian, allowing us to derive an asymptotic metric for the monopole wall moduli space.

  13. Pulsation at the tip of the first giant branch?

    NASA Astrophysics Data System (ADS)

    Ita, Yoshifusa; Tanabé, Toshihiko; Matsunaga, Noriyuki; Nakajima, Yasushi; Nagashima, Chie; Nagayama, Takahiro; Kato, Daisuke; Kurita, Mikio; Nagata, Tetsuya; Sato, Shuji; Tamura, Motohide; Nakaya, Hidehiko; Nakada, Yoshikazu

    2002-12-01

    The first results of our ongoing near-infrared (NIR) survey of the variable red giants in the Large Magellanic Cloud, using the Infrared Survey Facility (IRSF) and the SIRIUS infrared camera, are presented. Many very red stars were detected and we found that most of them are variables. In the observed colour-magnitude diagram (J-K, K) and the stellar K magnitude distribution, the tip of the first giant branch (TRGB), where helium burning in the core starts, is clearly seen. Apart from the genuine AGB variables, we found many variable stars at luminosities around the TRGB. From this result, we infer that a substantial fraction of them are RGB variables.

  14. Phase-lag Distances of OH Masing AGB Stars

    NASA Astrophysics Data System (ADS)

    Engels, D.; Etoka, S.; Gérard, E.; Richards, A.

    2015-08-01

    Distances to AGB stars with optically thick circumstellar shells cannot be determined using optical parallaxes. However, for stars with OH 1612 MHz maser emission emanating from their circumstellar shells, distances can be determined by the phase-lag method. This method combines a linear diameter obtained from a phase-lag measurement with an angular diameter obtained from interferometry. The phase-lag of the variable emission from the back and front sides of the shells has been determined for 20 OH/IR stars in the galactic disk. These measurements are based on a monitoring program with the Nançay radio telescope ongoing for more than 6 years. The interferometric observations are continuing. We estimate that the uncertainties of the distance determination will be ˜20%.

  15. Chemical evolution of fluorine in the bulge. High-resolution K-band spectra of giants in three fields

    NASA Astrophysics Data System (ADS)

    Jönsson, H.; Ryde, N.; Harper, G. M.; Cunha, K.; Schultheis, M.; Eriksson, K.; Kobayashi, C.; Smith, V. V.; Zoccali, M.

    2014-04-01

    Context. Possible main formation sites of fluorine in the Universe include asymptotic giant branch (AGB) stars, the ν-process in Type II supernova, and/or Wolf-Rayet stars. The importance of the Wolf-Rayet stars has theoretically been questioned and they are probably not needed in modeling the chemical evolution of fluorine in the solar neighborhood. It has, however, been suggested that Wolf-Rayet stars are indeed needed to explain the chemical evolution of fluorine in the bulge. The molecular spectral data, needed to determine the fluorine abundance, of the often used HF-molecule has not been presented in a complete and consistent way and has recently been debated in the literature. Aims: We intend to determine the trend of the fluorine-oxygen abundance ratio as a function of a metallicity indicator in the bulge to investigate the possible contribution from Wolf-Rayet stars. Additionally, we present here a consistent HF line list for the K- and L-bands including the often used 23 358.33 Å line. Methods: High-resolution near-infrared spectra of eight K giants were recorded using the spectrograph CRIRES mounted at the VLT. A standard setting was used that covered the HF molecular line at 23 358.33 Å. The fluorine abundances were determined using spectral fitting. We also re-analyzed five previously published bulge giants observed with the Phoenix spectrograph on Gemini using our new HF molecular data. Results: We find that the fluorine-oxygen abundance in the bulge probably cannot be explained with chemical evolution models that only include AGB stars and the ν-process in supernovae Type II, that is a significant amount of fluorine production in Wolf-Rayet stars is most likely needed to explain the fluorine abundance in the bulge. For the HF line data, we find that a possible reason for the inconsistencies in the literature, where two different excitation energies were used, is two different definitions of the zero-point energy for the HF molecule and therefore

  16. Post-AGB Stars in the Halos of Nearby Galaxies

    NASA Astrophysics Data System (ADS)

    Bond, Howard E.

    1999-02-01

    The visually brightest members of Population II are post-AGB (PAGB) stars evolving through spectral types F and A. The aim of this proposal is to find such PAGB stars in the halos of three galaxies that lie just outside the Local Group: Sextans A, NGC 3109, and NGC 5237. The importance of PAGB stars is: (1) they can probe the structure of galactic halos, in the form of test particles much more numerous than planetary nebulae or globular clusters, with which we can look for features such as clumps or tidal streams; (2) the number counts will tell us the theoretically poorly known transition time from AGB to planetary nebula; and (3) we believe that PAGB stars will prove to be a superb new PRIMARY distance indicator, comparable to or better than Cepheids. PAGB stars of types F and A are easily recognized because of their large Balmer jumps. Our uBVI photometric system is optimal for revealing them in galactic halos, due to their unique u-B colors, and the method is extremely efficient in its telescope time requirements. Sextans A and NGC 3109 have Cepheid and TRGB distances, so they are excellent test beds for a confrontation with our proposed Pop II primary standard candles. NGC 5237 has an uncertain distance, which PAGB stars should considerably improve. The 0.9-m telescope will be used (1) to obtain uBVI calibrations of our fields, thus saving the 4-m BTC mosaic for the deep observations; and (2) to complete our survey of Milky Way globular clusters for PAGB stars to used as Galactic calibrators of their luminosities and metallicity dependence.

  17. Post-AGB Stars in the Halos of Nearby Galaxies

    NASA Astrophysics Data System (ADS)

    Bond, Howard E.

    1999-02-01

    The visually brightest members of Population II are post-AGB (PAGB) stars evolving through spectral types F and A. The aim of this proposal is to find such PAGB stars in the halos of Sextans A and B (two galaxies just outside the Local Group) and of NGC 4236 (a nearly edge-on spiral in the M81 Group). The importance of these stars is: (1) they will serve as probes of the structure of galactic halos, in the form of test particles much more numerous than planetary nebulae or globular clusters, with which we can look for features such as clumps or tidal streams; (2) the number counts will tell us the theoretically poorly known transition time from AGB to planetary nebula; and (3) we believe that PAGB stars will prove to be a superb new PRIMARY distance indicator, comparable to or better than Cepheids. PAGB stars of types F and A are easily recognized because of their large Balmer jumps. Our uBVI photometric system is optimal for revealing them in galactic halos, due to their unique u-B colors, and the method is extremely efficient in its telescope time requirements. In Sextans A and B PAGB stars will appear at V~eq22.3, and in NGC 4236 at V~eq24. Sextans A and B have Cepheid and TRGB distances, and NGC 4236 is a Tully-Fisher calibrator, so they are excellent test beds for a confrontation with our proposed Pop II primary standard candles. We will use the 0.9-m telescope for uBVI calibrations of our fields, saving the 4-m for the deep observations.

  18. Polynomial Asymptotes of the Second Kind

    ERIC Educational Resources Information Center

    Dobbs, David E.

    2011-01-01

    This note uses the analytic notion of asymptotic functions to study when a function is asymptotic to a polynomial function. Along with associated existence and uniqueness results, this kind of asymptotic behaviour is related to the type of asymptote that was recently defined in a more geometric way. Applications are given to rational functions and…

  19. 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.

  20. Asymptotic vacua with higher derivatives

    NASA Astrophysics Data System (ADS)

    Cotsakis, Spiros; Kadry, Seifedine; Kolionis, Georgios; Tsokaros, Antonios

    2016-04-01

    We study limits of vacuum, isotropic universes in the full, effective, four-dimensional theory with higher derivatives. We show that all flat vacua as well as general curved ones are globally attracted by the standard, square root scaling solution at early times. Open vacua asymptote to horizon-free, Milne states in both directions while closed universes exhibit more complex logarithmic singularities, starting from initial data sets of a possibly smaller dimension. We also discuss the relation of our results to the asymptotic stability of the passage through the singularity in ekpyrotic and cyclic cosmologies.

  1. Asymptotic Rayleigh instantaneous unit hydrograph

    USGS Publications Warehouse

    Troutman, B.M.; Karlinger, M.R.

    1988-01-01

    The instantaneous unit hydrograph for a channel network under general linear routing and conditioned on the network magnitude, N, tends asymptotically, as N grows large, to a Rayleigh probability density function. This behavior is identical to that of the width function of the network, and is proven under the assumption that the network link configuration is topologically random and the link hydraulic and geometric properties are independent and identically distributed random variables. The asymptotic distribution depends only on a scale factor, {Mathematical expression}, where ?? is a mean link wave travel time. ?? 1988 Springer-Verlag.

  2. Integrated Properties of AGB Stars in Resolved and Unresolved Stellar Populations: Simple Stellar Populations and Star Clusters

    NASA Astrophysics Data System (ADS)

    Lançon, A.

    2011-09-01

    The evolution of AGB stars is notoriously complex. The confrontation of AGB population models with observed stellar populations is a useful alternative to the detailed study of individual stars in efforts to converge towards a reliable evolution theory. I review here the impact of studies of star clusters on AGB models and AGB population synthesis, deliberately leaving out any more complex stellar populations. Over the last 10 years, despite much effort, the absolute uncertainties in the predictions of the light emitted by intermediate-age populations have not been reduced to a satisfactory level. Observational sample definitions, as well as the combination of the natural variance in AGB properties with small number statistics, are largely responsible for this situation. There is hope that the constraints may soon become strong enough, thanks to large unbiased surveys of star clusters, resolved colour-magnitude diagrams, and new analysis methods that can account for the stochastic nature of AGB populations in clusters.

  3. AKARI All-Sky Survey: Contribution from AGB Stars to the Far Infrared Flux of the Milky Way

    NASA Astrophysics Data System (ADS)

    Pollo, A.; Rybka, P.; Takeuchi, T. T.

    2011-09-01

    Using the data from the AKARI FIS All-Sky Survey, we estimate the contribution from AGB stars to the far-infrared (FIR) flux from the Milky Way. We check the positions of different types of AGB stars in FIR color-color diagrams. Our conclusion is a large contribution from AGB stars, and particularly post-AGB stars, to the FIR flux in the outer regions of the Milky Way, and possibly other similar galaxies. FIR colors of different types of AGB stars are similar, with a large scatter, but post-AGB stars seem to be significantly redder and, as a result, contribute more to the total Galaxy flux at longer FIR wavelengths.

  4. Asymptotic Statistics of Cycles in Surrogate-Spatial Permutations

    NASA Astrophysics Data System (ADS)

    Bogachev, Leonid V.; Zeindler, Dirk

    2015-02-01

    We propose an extension of the Ewens measure on permutations by choosing the cycle weights to be asymptotically proportional to the degree of the symmetric group. This model is primarily motivated by a natural approximation to the so-called spatial random permutations recently studied by Betz and Ueltschi (hence the name "surrogate-spatial"), but it is of substantial interest in its own right. We show that under the suitable (thermodynamic) limit both measures have the similar critical behaviour of the cycle statistics characterized by the emergence of infinitely long cycles. Moreover, using a greater analytic tractability of the surrogate-spatial model, we obtain a number of new results about the asymptotic distribution of the cycle lengths (both small and large) in the full range of subcritical, critical, and supercritical domains. In particular, in the supercritical regime there is a parametric "phase transition" from the Poisson-Dirichlet limiting distribution of ordered cycles to the occurrence of a single giant cycle. Our techniques are based on the asymptotic analysis of the corresponding generating functions using Pólya's Enumeration Theorem and complex variable methods.

  5. 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.

  6. Asymptotic Safety in quantum gravity

    NASA Astrophysics Data System (ADS)

    Nink, Andreas; Reuter, Martin; Saueressig, Frank

    2013-06-01

    Asymptotic Safety (sometimes also referred to as nonperturbative renormalizability) is a concept in quantum field theory which aims at finding a consistent and predictive quantum theory of the gravitational field. Its key ingredient is a nontrivial fixed point of the theory's renormalization group flow which controls the behavior of the coupling constants in the ultraviolet (UV) regime and renders physical quantities safe from divergences. Although originally proposed by Steven Weinberg to find a theory of quantum gravity the idea of a nontrivial fixed point providing a possible UV completion can be applied also to other field theories, in particular to perturbatively nonrenormalizable ones. The essence of Asymptotic Safety is the observation that nontrivial renormalization group fixed points can be used to generalize the procedure of perturbative renormalization. In an asymptotically safe theory the couplings do not need to be small or tend to zero in the high energy limit but rather tend to finite values: they approach a nontrivial UV fixed point. The running of the coupling constants, i.e. their scale dependence described by the renormalization group (RG), is thus special in its UV limit in the sense that all their dimensionless combinations remain finite. This suffices to avoid unphysical divergences, e.g. in scattering amplitudes. The requirement of a UV fixed point restricts the form of the bare action and the values of the bare coupling constants, which become predictions of the Asymptotic Safety program rather than inputs. As for gravity, the standard procedure of perturbative renormalization fails since Newton's constant, the relevant expansion parameter, has negative mass dimension rendering general relativity perturbatively nonrenormalizable. This has driven the search for nonperturbative frameworks describing quantum gravity, including Asymptotic Safety which -- in contrast to other approaches -- is characterized by its use of quantum field theory

  7. 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.

  8. 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.

  9. Giant Cell Arteritis

    MedlinePlus

    Giant cell arteritis is a disorder that causes inflammation of your arteries, usually in the scalp, neck, and arms. ... arteries, which keeps blood from flowing well. Giant cell arteritis often occurs with another disorder called polymyalgia ...

  10. 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).

  11. Silicate features in Galactic and extragalactic post-AGB discs

    NASA Astrophysics Data System (ADS)

    Gielen, C.; Bouwman, J.; van Winckel, H.; Lloyd Evans, T.; Woods, P. M.; Kemper, F.; Marengo, M.; Meixner, M.; Sloan, G. C.; Tielens, A. G. G. M.

    2011-09-01

    Aims: In this paper we study the Spitzer and TIMMI2 infrared spectra of post-AGB disc sources, both in the Galaxy and the LMC. Using the observed infrared spectra we determine the mineralogy and dust parameters of the discs, and look for possible differences between the Galactic and extragalactic sources. Methods: Modelling the full spectral range observed allows us to determine the dust species present in the disc and different physical parameters such as grain sizes, dust abundance ratios, and the dust and continuum temperatures. Results: We find that all the discs are dominated by emission features of crystalline and amorphous silicate dust. Only a few sample sources show features due to CO2 gas or carbonaceous molecules such as PAHs and C60 fullerenes. Our analysis shows that dust grain processing in these discs is strong, resulting in large average grain sizes and a very high crystallinity fraction. However, we do not find any correlations between the derived dust parameters and properties of the central source. There also does not seem to be a noticeable difference between the mineralogy of the Galactic and LMC sources. Even though the observed spectra are very similar to those of protoplanetary discs around young stars, showing similar mineralogy and strong grain processing, we do find evidence for differences in the physical and chemical processes of the dust processing. Based on observations obtained at the European Southern Observatory (ESO), La Silla, observing program 072.D-0263 and 077.D-0555, and on observations made with the Spitzer Space Telescope (program id 3274 and 50092), which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA.Appendix A is available in electronic form at http://www.aanda.org

  12. Giant impacts on giant planets

    NASA Astrophysics Data System (ADS)

    de Pater, Imke

    2012-10-01

    The 2009 impact on Jupiter caught the world by surprise and cast doubt on impactor flux estimates for the outer solar system. Enhanced amateur planetary imaging techniques yield both high spatial resolution {enabling the 2009 impact debris field detection} and rapid frame rates {enabling the 2010 impact flash detections and lightcurve measurements}.We propose a Target of Opportunity program to image future impacts on Jupiter and Saturn. To remove the possibility of impact cloud non-detections, the program will be triggered only if an existing impact debris field is seen, an object on a collision course with Jupiter or Saturn is discovered, or an impact light curve is measured with an estimated total energy large enough to generate an impact cloud in a giant planet atmosphere.HST provides the only way to image these events in the ultraviolet, providing information on aerosol altitudes and on smaller particles that are less visible to ground-based infrared observations. High-resolution imaging with proper timing {not achievable from the ground} is required to measure precisely both the velocity fields of impact sites and the optical spectrum of impact debris. HST observations of past impacts on Jupiter have also served both as cornerstones of science investigations at other wavelengths and as vehicles for effective public outreach.Large outer solar system impacts are governed by the same physics as in the terrestrial events that dominate the impact threat to humans. Studying the behavior of impactors of various sizes and compositions, as they enter the atmosphere at varying angles and speeds, will better quantify terrestrial impact hazards.

  13. Giant impacts on giant planets

    NASA Astrophysics Data System (ADS)

    de Pater, Imke

    2014-10-01

    The 2009 impact and recent superbolides on Jupiter caught the world by surprise and cast doubt on impactor flux estimates for the outer solar system. Enhanced amateur planetary imaging techniques yield both high spatial resolution (enabling the 2009 impact debris field detection) and rapid frame rates (enabling the 2010/2012 impact flash detections and lightcurve measurements).We propose a ToO program to image future impacts on Jupiter and Saturn. To remove the possibility of impact cloud non-detections, the program will be triggered only if an existing impact debris field is seen, an object on a collision course with Jupiter or Saturn is discovered, or an impact light curve is measured with an estimated total energy large enough to generate an impact cloud in a giant planet atmosphere (10^20 J).HST provides the only way to image these events in the ultraviolet, providing information on aerosol altitudes and on smaller particles that are less visible to ground-based infrared observations. High-resolution imaging with proper timing (not achievable from the ground) is required to measure precisely both the velocity fields of impact sites and the optical spectrum of impact debris. HST observations of past impacts on Jupiter have also served both as cornerstones of science investigations at other wavelengths and as vehicles for effective public outreach.Large outer solar system impacts are governed by the same physics as in the terrestrial events that dominate the impact threat to humans. Studying the behavior of impactors of various sizes and compositions, as they enter the atmosphere at varying angles and speeds, will better quantify terrestrial impact hazards.

  14. Giant impacts on giant planets

    NASA Astrophysics Data System (ADS)

    de Pater, Imke

    2013-10-01

    The 2009 impact and recent superbolides on Jupiter caught the world by surprise and cast doubt on impactor flux estimates for the outer solar system. Enhanced amateur planetary imaging techniques yield both high spatial resolution {enabling the 2009 impact debris field detection} and rapid frame rates {enabling the 2010/2012 impact flash detections and lightcurve measurements}.We propose a ToO program to image future impacts on Jupiter and Saturn. To remove the possibility of impact cloud non-detections, the program will be triggered only if an existing impact debris field is seen, an object on a collision course with Jupiter or Saturn is discovered, or an impact light curve is measured with an estimated total energy large enough to generate an impact cloud in a giant planet atmosphere {10^20 J}.HST provides the only way to image these events in the ultraviolet, providing information on aerosol altitudes and on smaller particles that are less visible to ground-based infrared observations. High-resolution imaging with proper timing {not achievable from the ground} is required to measure precisely both the velocity fields of impact sites and the optical spectrum of impact debris. HST observations of past impacts on Jupiter have also served both as cornerstones of science investigations at other wavelengths and as vehicles for effective public outreach.Large outer solar system impacts are governed by the same physics as in the terrestrial events that dominate the impact threat to humans. Studying the behavior of impactors of various sizes and compositions, as they enter the atmosphere at varying angles and speeds, will better quantify terrestrial impact hazards.

  15. Higher dimensional nonclassical eigenvalue asymptotics

    NASA Astrophysics Data System (ADS)

    Camus, Brice; Rautenberg, Nils

    2015-02-01

    In this article, we extend Simon's construction and results [B. Simon, J. Funct. Anal. 53(1), 84-98 (1983)] for leading order eigenvalue asymptotics to n-dimensional Schrödinger operators with non-confining potentials given by Hn α = - Δ + ∏ i = 1 n |x i| α i on ℝn (n > 2), α ≔ ( α 1 , … , α n ) ∈ ( R+ ∗ ) n . We apply the results to also derive the leading order spectral asymptotics in the case of the Dirichlet Laplacian -ΔD on domains Ωn α = { x ∈ R n : ∏ j = 1 n }x j| /α j α n < 1 } .

  16. Asymptotic safety goes on shell

    NASA Astrophysics Data System (ADS)

    Benedetti, Dario

    2012-01-01

    It is well known in quantum field theory that the off-shell effective action depends on the gauge choice and field parametrization used in calculating it. Nevertheless, the typical scheme in which the scenario of asymptotically safe gravity is investigated is an off-shell version of the functional renormalization group equation. Working with the Einstein-Hilbert truncation as a test bed, we develop a new scheme for the analysis of asymptotically safe gravity in which the on-shell part of the effective action is singled out and we show that the beta function for the essential coupling has no explicit gauge dependence. In order to reach our goal, we introduce several technical novelties, including a different decomposition of the metric fluctuations, a new implementation of the ghost sector and a new cut-off scheme. We find a nontrivial fixed point, with a value of the cosmological constant that is independent of the gauge-fixing parameters.

  17. Asymptotic safety: A simple example

    SciTech Connect

    Braun, Jens; Gies, Holger; Scherer, Daniel D.

    2011-04-15

    We use the Gross-Neveu model in 2asymptotic safety scenario: despite being perturbatively nonrenormalizable, the model defines an interacting quantum field theory being valid to arbitrarily high momentum scales owing to the existence of a non-Gaussian fixed point. Using the functional renormalization group, we study the uv behavior of the model in both the purely fermionic as well as a partially bosonized language. We show that asymptotic safety is realized at non-Gaussian fixed points in both formulations, the universal critical exponents of which we determine quantitatively. The partially bosonized formulation allows to make contact to the large-N{sub f} expansion where the model is known to be renormalizable to all orders. In this limit, the fixed-point action as well as all universal critical exponents can be computed analytically. As asymptotic safety has become an important scenario for quantizing gravity, our description of a well-understood model is meant to provide for an easily accessible and controllable example of modern nonperturbative quantum field theory.

  18. 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.

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

    NASA Technical Reports Server (NTRS)

    Ake, T.

    1995-01-01

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

  20. Supersymmetric asymptotic safety is not guaranteed

    NASA Astrophysics Data System (ADS)

    Intriligator, Kenneth; Sannino, Francesco

    2015-11-01

    It was recently shown that certain perturbatively accessible, non-supersymmetric gauge-Yukawa theories have UV asymptotic safety, without asymptotic freedom: the UV theory is an interacting RG fixed point, and the IR theory is free. We here investigate the possibility of asymptotic safety in supersymmetric theories, and use unitarity bounds, and the a-theorem, to rule it out in broad classes of theories. The arguments apply without assuming perturbation theory. Therefore, the UV completion of a non-asymptotically free susy theory must have additional, non-obvious degrees of freedom, such as those of an asymptotically free (perhaps magnetic dual) extension.

  1. VizieR Online Data Catalog: Torun catalog of post-AGB and related objects (Szczerba+, 2007)

    NASA Astrophysics Data System (ADS)

    Szczerba, R.; Siodmiak, N.; Stasinska, G.; Borkowski, J.

    2007-09-01

    With the ongoing AKARI infrared sky survey, of much greater sensitivity than IRAS, a wealth of post-AGB objects may be discovered. It is thus time to organize our present knowledge of known post-AGB stars in the galaxy with a view to using it to search for new post-AGB objects among AKARI sources. We searched the literature available on the NASA Astrophysics Data System up to 1 October 2006, and defined criteria for classifying sources into three categories: very likely, possible and disqualified post-AGB objects. The category of very likely post-AGB objects is made up of several classes. We have created an evolutionary, on-line catalogue of Galactic post-AGB objects, to be referred to as the Torun catalogue of Galactic post-AGB and related objects. The present version of the catalogue contains 326 very likely, 107 possible and 64 disqualified objects. For the very likely post-AGB objects, the catalogue gives the available optical and infrared photometry, infrared spectroscopy and spectral types, and links to finding charts and bibliography. (3 data files).

  2. 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.

  3. 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.

  4. 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).

  5. Chromospheric Models and the Oxygen Abundance in Giant Stars

    NASA Astrophysics Data System (ADS)

    Dupree, A. K.; Avrett, E. H.; Kurucz, R. L.

    2016-04-01

    Realistic stellar atmospheric models of two typical metal-poor giant stars in Omega Centauri, which include a chromosphere (CHR), influence the formation of optical lines of O i: the forbidden lines (λ6300, λ6363) and the infrared triplet (λλ7771‑7775). One-dimensional semi-empirical non-local thermodynamic equilibrium (LTE) models are constructed based on observed Balmer lines. A full non-LTE formulation is applied for evaluating the line strengths of O i, including photoionization by the Lyman continuum and photoexcitation by Lyα and Lyβ. Chromospheric models (CHR) yield forbidden oxygen transitions that are stronger than those in radiative/convective equilibrium (RCE) models. The triplet oxygen lines from high levels also appear stronger than those produced in an RCE model. The inferred oxygen abundance from realistic CHR models for these two stars is decreased by factors of ∼3 as compared to values derived from RCE models. A lower oxygen abundance suggests that intermediate-mass AGB stars contribute to the observed abundance pattern in globular clusters. A change in the oxygen abundance of metal-poor field giants could affect models of deep mixing episodes on the red giant branch. Changes in the oxygen abundance can impact other abundance determinations that are critical to astrophysics, including chemical tagging techniques and galactic chemical evolution.

  6. The Hobby-Eberly Telescope Chemical Abundances of Stars in the Halo (CASH) Project. I. The Lithium-, s-, and r-enhanced Metal-poor Giant HKII 17435-00532

    NASA Astrophysics Data System (ADS)

    Roederer, Ian U.; Frebel, Anna; Shetrone, Matthew D.; Allende Prieto, Carlos; Rhee, Jaehyon; Gallino, Roberto; Bisterzo, Sara; Sneden, Christopher; Beers, Timothy C.; Cowan, John J.

    2008-06-01

    We present the first detailed abundance analysis of the metal-poor giant HKII 17435-00532. This star was observed as part of the University of Texas long-term project Chemical Abundances of Stars in the Halo (CASH). A spectrum was obtained with the High Resolution Spectrograph (HRS) on the Hobby-Eberly Telescope with a resolving power of R ~ 15,000. Our analysis reveals that this star may be located on the red giant branch, red horizontal branch, or early asymptotic giant branch. We find that this metal-poor ([Fe/H] = - 2.2) star has an unusually high lithium abundance [log ɛ (Li) = + 2.1], mild carbon ([C/Fe] = + 0.7) and sodium ([Na/Fe] = + 0.6) enhancement, as well as enhancement of both s-process ([Ba/Fe] = + 0.8) and r-process ([Eu/Fe] = + 0.5) material. The high Li abundance can be explained by self-enrichment through extra mixing that connects the convective envelope with the outer regions of the H-burning shell. If so, HKII 17435-00532 is the most metal-poor star in which this short-lived phase of Li enrichment has been observed. The Na and n-capture enrichment can be explained by mass transfer from a companion that passed through the thermally pulsing AGB phase of evolution with only a small initial enrichment of r-process material present in the birth cloud. Despite the current nondetection of radial velocity variations (over ~180 days), it is possible that HKII 17435-00532 is in a long-period or highly inclined binary system, similar to other stars with similar n-capture enrichment patterns. Based on observations obtained with the Hobby-Eberly Telescope, which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen.

  7. FUV and Optical Spectroscopy of Hot Post-AGB Stars in Globular Clusters

    NASA Technical Reports Server (NTRS)

    Dixon, William V.

    2004-01-01

    The goal of this program was to determine the atmospheric parameters (effective temperature and surface gravity) and abundances of the hot, post-AGB (PAGB) stars in globular clusters observed with the Hopkins Ultraviolet Telescope (HUT) on the Astro-l and 2 missions.

  8. AKARI All-Sky Far-Infrared Survey: Where to Look for AGB Stars?

    NASA Astrophysics Data System (ADS)

    Rybka, P.; Pollo, A.; Takeuchi, T. T.

    2011-09-01

    We selected a sample of 5,176 far-infrared sources from the FIS AKARI All-Sky Survey. Searching public databases, we identified their counterparts observed at other wavelengths and derived a method to separate stars from galaxies. The sample of stars is dominated by AGB-related objects.

  9. AGB Statement on Board Responsibility for the Oversight of Educational Quality

    ERIC Educational Resources Information Center

    Association of Governing Boards of Universities and Colleges, 2011

    2011-01-01

    This "Statement on Board Responsibility for the Oversight of Educational Quality," approved by the Board of Directors of the Association of Governing Boards (AGB) in March 2011, urges institutional administrators and governing boards to engage fully in this area of board responsibility. The seven principles in this statement offer suggestions to…

  10. The LF of TP-AGB stars in the LMC/SMC

    NASA Technical Reports Server (NTRS)

    Bruzual, Gustavo; Charlot, Stephane; GonzalezLopezlira, Rosa; Srinivasan, Sundar; Boyer, Martha L.

    2013-01-01

    We show that Monte Carlo simulations of the TP-AGB stellar population in the LMC and SMC galaxies using the CB. models produce LF and color distributions that are in closer agreement with observations than those obtained with the BC03 and CB07 models. This is a progress report of work that will be published elsewhere.

  11. The maximum drag reduction asymptote

    NASA Astrophysics Data System (ADS)

    Choueiri, George H.; Hof, Bjorn

    2015-11-01

    Addition of long chain polymers is one of the most efficient ways to reduce the drag of turbulent flows. Already very low concentration of polymers can lead to a substantial drag and upon further increase of the concentration the drag reduces until it reaches an empirically found limit, the so called maximum drag reduction (MDR) asymptote, which is independent of the type of polymer used. We here carry out a detailed experimental study of the approach to this asymptote for pipe flow. Particular attention is paid to the recently observed state of elasto-inertial turbulence (EIT) which has been reported to occur in polymer solutions at sufficiently high shear. Our results show that upon the approach to MDR Newtonian turbulence becomes marginalized (hibernation) and eventually completely disappears and is replaced by EIT. In particular, spectra of high Reynolds number MDR flows are compared to flows at high shear rates in small diameter tubes where EIT is found at Re < 100. The research leading to these results has received funding from the People Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme (FP7/2007-2013) under REA grant agreement n° [291734].

  12. Asymptotically Free Gauge Theories. I

    DOE R&D Accomplishments Database

    Wilczek, Frank; Gross, David J.

    1973-07-01

    Asymptotically free gauge theories of the strong interactions are constructed and analyzed. The reasons for doing this are recounted, including a review of renormalization group techniques and their application to scaling phenomena. The renormalization group equations are derived for Yang-Mills theories. The parameters that enter into the equations are calculated to lowest order and it is shown that these theories are asymptotically free. More specifically the effective coupling constant, which determines the ultraviolet behavior of the theory, vanishes for large space-like momenta. Fermions are incorporated and the construction of realistic models is discussed. We propose that the strong interactions be mediated by a "color" gauge group which commutes with SU(3)xSU(3). The problem of symmetry breaking is discussed. It appears likely that this would have a dynamical origin. It is suggested that the gauge symmetry might not be broken, and that the severe infrared singularities prevent the occurrence of non-color singlet physical states. The deep inelastic structure functions, as well as the electron position total annihilation cross section are analyzed. Scaling obtains up to calculable logarithmic corrections, and the naive lightcone or parton model results follow. The problems of incorporating scalar mesons and breaking the symmetry by the Higgs mechanism are explained in detail.

  13. Numerical Asymptotic Solutions Of Differential Equations

    NASA Technical Reports Server (NTRS)

    Thurston, Gaylen A.

    1992-01-01

    Numerical algorithms derived and compared with classical analytical methods. In method, expansions replaced with integrals evaluated numerically. Resulting numerical solutions retain linear independence, main advantage of asymptotic solutions.

  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. Induction and characterization of suppressor T cells and soluble factors with modified timothy grass pollen AgB.

    PubMed

    Malley, A; Deppe, L B; Brandt, C J

    1981-01-01

    Previous studies demonstrated that antigen B (AgB), a major antigen of timothy grass pollen, modified by photooxidation (Ox-AgB) does not react with rabbit, human, or mouse antibodies directed against AgB and does not induce antibodies reactive with either native or modified AgB. However, immunization of mice with Ox-AgB in alum induces significant T helper cell activity. In this review, we describe the conditions and kinetics for Ox-AgB induction of T suppressor cells, the secretion of AgB-specific T suppressor factor (TSF), and the partial purification of AgB-specific TSF. PMID:6453098

  16. VizieR Online Data Catalog: Galactic and MC O-AGBs and RSGs stars (Jones+, 2012)

    NASA Astrophysics Data System (ADS)

    Jones, O. C.; Kemper, F.; Sargent, B. A.; McDonald, I.; Gielen, C.; Woods, P. M.; Sloan, G. C.; Boyer, M. L.; Zijlstra, A. A.; Clayton, G. C.; Kraemer, K. E.; Srinivasan, S.; Ruffle, P. M. E.

    2015-11-01

    Our sample contains 69 oxygen-rich AGB stars (O-AGB) and 76 RSG stars in the Magellanic Clouds which were observed spectroscopically with Spitzer, and 131 Galactic field O-AGBs and RSGs observed with either Spitzer or ISO. The Spitzer spectra cover a wavelength range of 5.2-37.2um, while ISO spectra cover the 2.38-45.2um part of the spectrum. We combine this sample with 39 spectra from 14 GGCs to extend the low end of the metallicity range. (5 data files).

  17. Asymptotically optimal topological quantum compiling.

    PubMed

    Kliuchnikov, Vadym; Bocharov, Alex; Svore, Krysta M

    2014-04-11

    We address the problem of compiling quantum operations into braid representations for non-Abelian quasiparticles described by the Fibonacci anyon model. We classify the single-qubit unitaries that can be represented exactly by Fibonacci anyon braids and use the classification to develop a probabilistically polynomial algorithm that approximates any given single-qubit unitary to a desired precision by an asymptotically depth-optimal braid pattern. We extend our algorithm in two directions: to produce braids that allow only single-strand movement, called weaves, and to produce depth-optimal approximations of two-qubit gates. Our compiled braid patterns have depths that are 20 to 1000 times shorter than those output by prior state-of-the-art methods, for precisions ranging between 10(-10) and 10(-30). PMID:24765934

  18. Plane Wave and Coulomb Asymptotics

    NASA Astrophysics Data System (ADS)

    Mulligan, P. G.; Crothers, D. S. F.

    2004-01-01

    A simple plane wave solution of the Schrödinger Helmholtz equation is a quantum eigenfunction obeying both energy and linear momentum correspondence principles. Inclusion of the outgoing wave with scattering amplitude f obeys unitarity and the optical theorem. By closely considering the standard asymptotic development of the plane wave, we show that there is a problem with angular momentum when we consider forward scattering at the point of closest approach and at large impact parameter given semiclassically by (l + 1/2)/k where l is the azimuthal quantum number and may be large (J Leech et al, Phys. Rev. Lett. 88 257901 (2002)). The problem is resolved via non-uniform, non-standard analysis involving the Heaviside step function, unifying classical, semiclassical and quantum mechanics, and the treatment is extended to the case of pure Coulomb scattering.

  19. Period spacings in red giants. II. Automated measurement

    NASA Astrophysics Data System (ADS)

    Vrard, M.; Mosser, B.; Samadi, R.

    2016-04-01

    Context. The space missions CoRoT and Kepler have provided photometric data of unprecedented quality for asteroseismology. A very rich oscillation pattern has been discovered for red giants, including mixed modes that are used to decipher the red giants' interiors. They carry information on the radiative core of red giant stars and bring strong constraints on stellar evolution. Aims: Since more than 15 000 red giant light curves have been observed by Kepler, we have developed a simple and efficient method for automatically characterizing the mixed-mode pattern and measuring the asymptotic period spacing. Methods: With the asymptotic expansion of the mixed modes, we have revealed the regularity of the gravity-mode pattern. The stretched periods were used to study the evenly space periods with a Fourier analysis and to measure the gravity period spacing, even when rotation severely complicates the oscillation spectra. Results: We automatically measured gravity period spacing for more than 6100 Kepler red giants. The results confirm and extend previous measurements made by semi-automated methods. We also unveil the mass and metallicity dependence of the relation between the frequency spacings and the period spacings for stars on the red giant branch. Conclusions: The delivery of thousands of period spacings combined with all other seismic and non-seismic information provides a new basis for detailed ensemble asteroseismology. Full Table 2 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/588/A87

  20. Binary Systems of Core-collapse Supernovae Polluting a Giant Companion

    NASA Astrophysics Data System (ADS)

    Sabach, Efrat; Soker, Noam

    2015-06-01

    We examine binary systems where when the more massive star, the primary, explodes as a core-collapse supernova (SN), the secondary star is already a giant that intercepts a large fraction of the ejecta. The ejecta might pollute the secondary star with newly synthesized elements such as calcium. We use Modules for Experiments in Stellar Astrophysics to calculate the evolution of such SN-polluted giant (SNPG) binaries. We estimate that on average at any given time tens of SNPGs are present in the Galaxy, and ≈ 10 SNPG objects are present in the Magellanic Clouds. We speculate that the high calcium abundance of the recently discovered evolved star HV 2112 in the Small Magellanic Cloud might be the result of an SNPG with a super-AGB stellar secondary of mass ≈ 9 {{M}⊙ }. This rare SNPG scenario is an alternative explanation to HV 2112 being a Thorne-Żytkow object.

  1. Peripheral giant cell granuloma.

    PubMed

    Adlakha, V K; Chandna, P; Rehani, U; Rana, V; Malik, P

    2010-01-01

    Peripheral giant cell granuloma is a benign reactive lesion of gingiva. It manifests as a firm, soft, bright nodule or as a sessile or pedunculate mass. This article reports the management of peripheral giant cell granuloma in a 12-year-old boy by surgical excision. PMID:21273719

  2. 8. Asymptotically Flat and Regular Cauchy Data

    NASA Astrophysics Data System (ADS)

    Dain, Sergio

    I describe the construction of a large class of asymptotically flat initial data with non-vanishing mass and angular momentum for which the metric and the extrinsic curvature have asymptotic expansions at space-like infinity in terms of powers of a radial coordinate. I emphasize the motivations and the main ideas behind the proofs.

  3. Einstein-Yang-Mills theory: Asymptotic symmetries

    NASA Astrophysics Data System (ADS)

    Barnich, Glenn; Lambert, Pierre-Henry

    2013-11-01

    Asymptotic symmetries of the Einstein-Yang-Mills system with or without cosmological constant are explicitly worked out in a unified manner. In agreement with a recent conjecture, one finds a Virasoro-Kac-Moody type algebra not only in three dimensions but also in the four-dimensional asymptotically flat case.

  4. An asymptotic model of the F layer

    NASA Astrophysics Data System (ADS)

    Oliver, W. L.

    2012-01-01

    A model of the F layer of the ionosphere is presented that consists of a bottomside asymptote that ignores transport and a topside asymptote that ignores chemistry. The asymptotes connect at the balance height dividing the chemistry and transport regimes. A combination of these two asymptotes produces a good approximation to the true F layer. Analogously, a model of F layer response to an applied vertical drift is presented that consists of two asymptotic responses, one that ignores transport and one that ignores chemistry. The combination of these asymptotic responses produces a good approximation to the response of the true F layer. This latter response is identical to the “servo” response of Rishbeth et al. (1978), derived from the continuity equation. The asymptotic approach bypasses the continuity equation in favor of “force balance” arguments and so replaces a differential equation with simpler algebraic equations. This new approach provides a convenient and intuitive mean for first-order estimates of the change in F layer peak height and density in terms of changes in neutral density, composition, temperature, winds, and electric fields. It is applicable at midlatitudes and at magnetically quiet times at high latitudes. Forensic inverse relations are possible but are not unique. The validity of the asymptotic relations is shown through numerical simulation.

  5. A chemical route to the formation of water in circumstellar envelopes around carbon-rich asymptotic branch stars: Fischer-Tropsch catalysis

    NASA Technical Reports Server (NTRS)

    Willacy, K.

    2004-01-01

    Fischer-Tropsch catalysis has been suggested as a means of driving hydrocarbon chemistry in oxygen rich regions such as the protosolar nebula. In addition to producing hydrocarbons, Fischer-Tropsch catalysis also produces water, and it is therefore possible that such processes could account for the recent observations of water in the circumstellar envelope of asymptotic giant branch star IRC +10216.

  6. 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.

  7. The Impact of FUSE on our Understanding of Stellar Post-AGB Evolution

    SciTech Connect

    Rauch, T.; Werner, K.; Ziegler, M.; Koesterke, L.; Kruk, J. W.; Oliveira, C. M.

    2009-05-24

    State-of-the-art non-LTE spectral analysis requires high-resolution and high-S/N observations of strategic metal lines in order to achieve reliable photospheric parameters like, e.g., effective temperature, surface gravity, and element abundances.Hot stars with effective temperatures higher than about 40 000 K exhibit their metal-line spectrum arising from highly ionized species predominantly in the (far) ultraviolet wavelength range.FUSE observations of hot, compact stars provided the necessary data. With these, it has been, e.g., possible to identify fluorine for the first time in observations of post-AGB stars. The evaluation of ionization equilibria of highly ionized neon, phosphorus, sulfur, and argon provides a new sensitive tool to determine effective temperatures of the hottest stars precisely. Moreover, abundance determinations have put constraints on stellar evolutionary models which, in turn, have improved greatly our picture of post-AGB evolution.

  8. 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.

  9. Detecting communities using asymptotical surprise

    NASA Astrophysics Data System (ADS)

    Traag, V. A.; Aldecoa, R.; Delvenne, J.-C.

    2015-08-01

    Nodes in real-world networks are repeatedly observed to form dense clusters, often referred to as communities. Methods to detect these groups of nodes usually maximize an objective function, which implicitly contains the definition of a community. We here analyze a recently proposed measure called surprise, which assesses the quality of the partition of a network into communities. In its current form, the formulation of surprise is rather difficult to analyze. We here therefore develop an accurate asymptotic approximation. This allows for the development of an efficient algorithm for optimizing surprise. Incidentally, this leads to a straightforward extension of surprise to weighted graphs. Additionally, the approximation makes it possible to analyze surprise more closely and compare it to other methods, especially modularity. We show that surprise is (nearly) unaffected by the well-known resolution limit, a particular problem for modularity. However, surprise may tend to overestimate the number of communities, whereas they may be underestimated by modularity. In short, surprise works well in the limit of many small communities, whereas modularity works better in the limit of few large communities. In this sense, surprise is more discriminative than modularity and may find communities where modularity fails to discern any structure.

  10. A Pilot Deep Survey for X-Ray Emission from fuvAGB Stars

    NASA Astrophysics Data System (ADS)

    Sahai, R.; Sanz-Forcada, J.; Sánchez Contreras, C.; Stute, M.

    2015-09-01

    We report the results of a pilot survey for X-ray emission from a newly discovered class of AGB stars with far-ultraviolet excesses (fuvAGB stars) using XMM-Newton and Chandra. We detected X-ray emission in three of six fuvAGB stars observed—the X-ray fluxes are found to vary in a stochastic or quasi-periodic manner on roughly hour-long timescales, and simultaneous UV observations using the Optical Monitor on XMM for these sources show similar variations in the UV flux. These data, together with previous studies, show that X-ray emission is found only in fuvAGB stars. From modeling the spectra, we find that the observed X-ray luminosities are ˜(0.002-0.2) L⊙ and the X-ray-emitting plasma temperatures are ˜(35-160) × 106 K. The high X-ray temperatures argue against the emission arising in stellar coronae, or directly in an accretion shock, unless it occurs on a WD companion. However, none of the detected objects is a known WD-symbiotic star, suggesting that if WD companions are present, they are relatively cool (<20,000 K). In addition, the high X-ray luminosities specifically argue against emission originating in the coronae of main-sequence companions. 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 companion star, with confinement by strong magnetic fields associated with the companion and/or an accretion disk around it.

  11. Lithium and zirconium abundances in massive Galactic O-rich AGB stars

    NASA Astrophysics Data System (ADS)

    García-Hernández, D. A.; García-Lario, P.; Plez, B.; Manchado, A.; D'Antona, F.; Lub, J.; Habing, H.

    2007-02-01

    Lithium and zirconium abundances (the latter taken as representative of s-process enrichment) are determined for a large sample of massive Galactic O-rich AGB stars, for which high-resolution optical spectroscopy has been obtained (R˜ 40 000{-}50 000). This was done by computing synthetic spectra based on classical hydrostatic model atmospheres for cool stars and using extensive line lists. The results are discussed in the framework of "hot bottom burning" (HBB) and nucleosynthesis models. The complete sample is studied for various observational properties such as the position of the stars in the IRAS two-colour diagram ([ 12] - [25] vs. [ 25] - [60] ), Galactic distribution, expansion velocity (derived from the OH maser emission), and period of variability (when available). We conclude that a considerable fraction of these sources are actually massive AGB stars (M>3{-}4 M⊙) experiencing HBB, as deduced from the strong Li overabundances we found. A comparison of our results with similar studies carried out in the past for the Magellanic Clouds (MCs) reveals that, in contrast to MC AGB stars, our Galactic sample does not show any indication of s-process element enrichment. The differences observed are explained as a consequence of metallicity effects. Finally, we discuss the results obtained in the framework of stellar evolution by comparing our results with the data available in the literature for Galactic post-AGB stars and PNe. Based on observations at the 4.2 m William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de Los Muchachos of the Instituto de Astrofisica de Canarias. Also based on observations with the ESO 3.6 m telescope at La Silla Observatory (Chile). Tables [see full text]-[see full text] are only available in electronic form at http://www.aanda.org

  12. 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.

  13. 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.

  14. Unstable giant gravitons

    SciTech Connect

    Mello Koch, Robert de; Ives, Norman; Smolic, Jelena; Smolic, Milena

    2006-03-15

    We find giant graviton solutions in Frolov's three parameter generalization of the Lunin-Maldacena background. The background we study has {gamma}-tilde{sub 1}=0 and {gamma}-tilde{sub 2}={gamma}-tilde{sub 3}={gamma}-tilde. This class of backgrounds provides a nonsupersymmetric example of the gauge theory/gravity correspondence that can be tested quantitatively, as recently shown by Frolov, Roiban, and Tseytlin. The giant graviton solutions we find have a greater energy than the point gravitons, making them unstable states. Despite this, we find striking quantitative agreement between the gauge theory and gravity descriptions of open strings attached to the giant.

  15. 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.

  16. 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.

  17. VLT/NACO Imaging of the Nearest AGB Star, L2 Puppis

    NASA Astrophysics Data System (ADS)

    Montargès, M.; Kervella, P.; Ridgway, S. T.; Perrin, G.; Chesneau, O.

    2015-08-01

    AGB stars are the most important contributors to the chemical enrichment of the Galaxy. During their later evolutionary stages they experience intense pulsations and eject most of their layers as they become planetary nebulae (PNe). The process leading to the formation of bipolar PNe remains poorly understood. It is assumed that the circumstellar disk of an AGB star could collimate the stellar wind to form a bipolar PN, yet very few of these disks have been observed. Using the adaptive-optics system of the VLT/NACO instrument at the Paranal Observatory and a "lucky imaging" technique, our team obtained near-infrared diffraction-limited images of the nearest AGB star, L2 Puppis. The deconvolved images reveal a dark structure in front of the star whose morphology and photometry match a dusty edge-on disk of olivine and pyroxene modeled with a Monte-Carlo radiative transfer code. The L band images also show a loop structure, possibly the signature of an interacting hidden companion.

  18. Giant distal humeral geode.

    PubMed

    Maher, M M; Kennedy, J; Hynes, D; Murray, J G; O'Connell, D

    2000-03-01

    We describe the imaging features of a giant geode of the distal humerus in a patient with rheumatoid arthritis, which presented initially as a pathological fracture. The value of magnetic resonance imaging in establishing this diagnosis is emphasized. PMID:10794554

  19. Giant Subclavian Artery Aneurysm.

    PubMed

    Counts, Sarah; Zeeshan, Ahmad; Elefteriades, John

    2016-06-01

    We report the case of a 37-year-old construction executive presenting with chest pain, shortness of breath, and dizziness on exertion secondary to a giant left subclavian artery aneurysm and aortic valvular disease. PMID:27231430

  20. The Next Giant Step

    NASA Video Gallery

    Artist Robert McCall painted "The Next Giant Step" in 1979 to commemorate the heroism and courage of spaceflight pioneers. Located in the lobby of Johnson's building 2, the mural depicts America's ...

  1. The Giant Cell.

    ERIC Educational Resources Information Center

    Stockdale, Dennis

    1998-01-01

    Provides directions for the construction of giant plastic cells, including details for building and installing the organelles. Also contains instructions for preparing the ribosomes, nucleolus, nucleus, and mitochondria. (DDR)

  2. Explosive Percolation with Multiple Giant Components

    NASA Astrophysics Data System (ADS)

    Chen, Wei; D'Souza, Raissa M.

    2011-03-01

    We generalize the random graph evolution process of Bohman, Frieze, and Wormald [T. Bohman, A. Frieze, and N. C. Wormald, Random Struct. AlgorithmsRSALFD1042-983210.1002/rsa.20038, 25, 432 (2004)]. Potential edges, sampled uniformly at random from the complete graph, are considered one at a time and either added to the graph or rejected provided that the fraction of accepted edges is never smaller than a decreasing function asymptotically approaching the value α=1/2. We show that multiple giant components appear simultaneously in a strongly discontinuous percolation transition and remain distinct. Furthermore, tuning the value of α determines the number of such components with smaller α leading to an increasingly delayed and more explosive transition. The location of the critical point and strongly discontinuous nature are not affected if only edges which span components are sampled.

  3. 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).

  4. EMC effect: asymptotic freedom with nuclear targets

    SciTech Connect

    West, G.B.

    1984-01-01

    General features of the EMC effect are discussed within the framework of quantum chromodynamics as expressed via the operator product expansion and asymptotic freedom. These techniques are reviewed with emphasis on the target dependence. 22 references.

  5. Hermite polynomials and quasi-classical asymptotics

    SciTech Connect

    Ali, S. Twareque; Engliš, Miroslav

    2014-04-15

    We study an unorthodox variant of the Berezin-Toeplitz type of quantization scheme, on a reproducing kernel Hilbert space generated by the real Hermite polynomials and work out the associated quasi-classical asymptotics.

  6. Low-mass companions to Bright Giants

    NASA Astrophysics Data System (ADS)

    Niedzielski, A.; Wolszczan, A.; Nowak, G.; Adamów, M.; Deka, B.; Górecka, M.; Kowalik, K.

    2014-04-01

    Asymmetric Planetary Nebulae (APN) are formed by bipolar outflows through various mechanism like fast rotation (Blackman et al. 2001), magnetic field (Regos & Tout 1995) or binarity (Harpaz & Soker 1994; Soker 1996; Livio & Soker 2002). The binary scenario seems currently to be best supported by observations as the most efficient in producing the observed APN (De Marco et al. 2004; Soker 2006). Detailed studies of disk formation in binaries leading to APN were presented for instance in Reyes-Ruiz & Lopez (1999), Blackman et al. (2001) and Nordhaus & Blackman (2006). To estimate relative efficiently of the various channels of APN production properties of the population of stars to become AGB stars have to be known. Here our RV search for planets around evolved stars the Penn State-Torun Centre for Astronomy Planet Search (PTPS), whose primary, long-term goal is to improve our understanding of the evolution of planetary systems around aging stars (Niedzielski et al. 2007; Niedzielski & Wolszczan 2008) may be of some help. 1036 stars are monitored within PTPS with the Hobby-Eberly Telescope (HET, Ramsey et al. 1998) and its High Resolution Spectrograph (HRS, Tull et al. 1998) for RV variations using the high precision iodine-cell technique since 2004. The sample is mainly composed of evolved low- and intermediate- mass single or SB1 stars: 449 giants (including 343 clump giants) and 297 subgiants but it also contains 151 slightly evolved dwarfs. All SB1 and SB2 stellar-mass binaries have been identified in the sample. Detailed spectroscopic analysis of 348 stars, mostly giants has been completed by Zieliński et al. (2012). Similar analyses for 403 giants and subgiants (Niedzielski et. al. in prep.) and 146 dwarf (Deka et al. in prep.) are in preparation. In addition to stellar atmospheric parameters the spectroscopic studies deliver masses and luminosities (through fits to evolutionary tracks) as well as ages required for further considerations on planetary

  7. Charting the Giants

    NASA Astrophysics Data System (ADS)

    2004-06-01

    zero expansion asymptotically after an infinite time and has a flat geometry). All three observational tests by means of supernovae (green), the cosmic microwave background (blue) and galaxy clusters converge at a Universe around Ωm ~ 0.3 and ΩΛ ~ 0.7. The dark red region for the galaxy cluster determination corresponds to 95% certainty (2-sigma statistical deviation) when assuming good knowledge of all other cosmological parameters, and the light red region assumes a minimum knowledge. For the supernovae and WMAP results, the inner and outer regions corespond to 68% (1-sigma) and 95% certainty, respectively. References: Schuecker et al. 2003, A&A, 398, 867 (REFLEX); Tonry et al. 2003, ApJ, 594, 1 (supernovae); Riess et al. 2004, ApJ, 607, 665 (supernovae) Galaxy clusters are far from being evenly distributed in the Universe. Instead, they tend to conglomerate into even larger structures, "super-clusters". Thus, from stars which gather in galaxies, galaxies which congregate in clusters and clusters tying together in super-clusters, the Universe shows structuring on all scales, from the smallest to the largest ones. This is a relict of the very early (formation) epoch of the Universe, the so-called "inflationary" period. At that time, only a minuscule fraction of one second after the Big Bang, the tiny density fluctuations were amplified and over the eons, they gave birth to the much larger structures. Because of the link between the first fluctuations and the giant structures now observed, the unique REFLEX catalogue - the largest of its kind - allows astronomers to put considerable constraints on the content of the Universe, and in particular on the amount of dark matter that is believed to pervade it. Rather interestingly, these constraints are totally independent from all other methods so far used to assert the existence of dark matter, such as the study of very distant supernovae (see e.g. ESO PR 21/98) or the analysis of the Cosmic Microwave background (e

  8. First detection of surface magnetic fields in post-AGB stars: the cases of U Monocerotis and R Scuti

    NASA Astrophysics Data System (ADS)

    Sabin, L.; Wade, G. A.; Lèbre, A.

    2015-01-01

    While several observational investigations have revealed the presence of magnetic fields in the circumstellar envelopes, jets and outflows of post-asymptotic giant branch stars (PAGBs) and planetary nebulae, none has clearly demonstrated their presence at the stellar surface. The lack of information on the strength of the surface magnetic fields prevents us from performing any thorough assessment of their dynamic capability (i.e. material mixing, envelope shaping, etc). We present new high-resolution spectropolarimetric (Stokes V) observations of a sample of PAGB stars, realized with the instruments ESPaDOnS and Narval, where we searched for the presence of photospheric magnetic fields. Out of the seven targets investigated, the RV Tauri stars U Mon and R Sct display a clear Zeeman signature and return a definite detection after performing a least squares deconvolution analysis. The remaining five PAGBs show no significant detection. We derived longitudinal magnetic fields of 10.2 ± 1.7 G for U Mon and 0.6 ± 0.6 G for R Sct. In both cases, the Stokes profiles point towards an interaction of the magnetic field with the atmosphere dynamics. This first discovery of weak magnetic fields (e.g. ˜10 G level) at the stellar surface of PAGB stars opens the door to a better understanding of magnetism in evolved stars.

  9. H2O maser emission in circumstellar envelopes around AGB stars: Physical conditions in gas-dust clouds

    NASA Astrophysics Data System (ADS)

    Nesterenok, A. V.

    2013-10-01

    The pumping of 22.2-GHz H2O masers in the circumstellar envelopes of asymptotic giant branch stars has been simulated numerically. The physical parameters adopted in the calculations correspond to those of the circumstellar envelope around IK Tau. The one-dimensional plane-parallel structure of the gas-dust cloud is considered. The statistical equilibrium equations for the H2O level populations and the thermal balance equations for the gas-dust cloud are solved self-consistently. The calculations take into account 410 rotational levels belonging to the five lowest vibrational levels of H2O. The stellar radiation field is shown to play an important role in the thermal balance of the gas-dust cloud due to the absorption of emission in rotational-vibrational H2O lines. The dependence of the gain in the 22.2-GHz maser line on the gas density and H2O number density in the gas-dust cloud is investigated. Gas densities close to the mean density of the stellar wind, 107-108 cm-3, and a high relative H2O abundance, more than 10-4, have been found to be the most likely physical conditions in maser sources.

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

    NASA Technical Reports Server (NTRS)

    Ake, T.

    1995-01-01

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

  11. Compact reflection nebulae, a transit phase of evolution from post-AGB to planetary nebulae

    NASA Technical Reports Server (NTRS)

    Hu, J. Y.; Slijkhuis, S.

    1989-01-01

    In a search of the optical counter-part of candidates of protoplanetary nebulae on the plates of UK Schmidt, ESO Schmidt, and POSS, five compact reflection nebulae associated with post-AGB stars were found. A simplified model (dust shell is spherical symmetric, expansion velocity of dust shell is constant, Q(sub sca)(lambda) is isotropic, and the dust grain properties are uniform) is used to estimate the visible condition of the dust shell due to the scattering of the core star's light. Under certain conditions the compact reflection nebulae can be seen of the POSS or ESO/SRC survey plates.

  12. 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.

  13. Giant perigenital seborrheic keratosis

    PubMed Central

    Bandyopadhyay, Debabrata; Saha, Abanti; Mishra, Vivek

    2015-01-01

    Seborrheic keratosis (SK) is a very common benign epidermal proliferation that is prevalent in all races. Most commonly occurring on the trunk, face, scalp, and the extremities, they can occur anywhere on the body except the palms and soles. The most common appearance is that of a very superficial verrucous plaque which appears to be stuck on the surface. Giant lesions are very rare, and their location on the genital area is rarer still. We report here a case of multiple giant SK lesions in a 59-year-old man. PMID:25657917

  14. An Innocent Giant

    PubMed Central

    Solanki, Lakhan Singh; Dhingra, Mandeep; Raghubanshi, Gunjan; Thami, Gurvinder Pal

    2014-01-01

    A cutaneous horn (cornu cutaneum) is a protrusion from the skin composed of a cornified material. It may be associated with a benign, premalignant, or malignant lesion at the base, masking numerous dermatoses. In a 24-year-old female, a giant cutaneous horn arising from a seborrheic keratosis located on the leg is presented. This case has been reported to emphasize that a giant cutaneous horn may also occur in young patients, even in photoprotected areas, and are not always associated with malignancy. PMID:25484426

  15. Giant perigenital seborrheic keratosis.

    PubMed

    Bandyopadhyay, Debabrata; Saha, Abanti; Mishra, Vivek

    2015-01-01

    Seborrheic keratosis (SK) is a very common benign epidermal proliferation that is prevalent in all races. Most commonly occurring on the trunk, face, scalp, and the extremities, they can occur anywhere on the body except the palms and soles. The most common appearance is that of a very superficial verrucous plaque which appears to be stuck on the surface. Giant lesions are very rare, and their location on the genital area is rarer still. We report here a case of multiple giant SK lesions in a 59-year-old man. PMID:25657917

  16. Maximal hypersurfaces in asymptotically stationary spacetimes

    NASA Astrophysics Data System (ADS)

    Chrusciel, Piotr T.; Wald, Robert M.

    1992-12-01

    The purpose of the work is to extend the results on the existence of maximal hypersurfaces to encompass some situations considered by other authors. The existence of maximal hypersurface in asymptotically stationary spacetimes is proven. Existence of maximal surface and of foliations by maximal hypersurfaces is proven in two classes of asymptotically flat spacetimes which possess a one parameter group of isometries whose orbits are timelike 'near infinity'. The first class consists of strongly causal asymptotically flat spacetimes which contain no 'blackhole or white hole' (but may contain 'ergoregions' where the Killing orbits fail to be timelike). The second class of space times possess a black hole and a white hole, with the black and white hole horizon intersecting in a compact 2-surface S.

  17. Dispersive shock wave interactions and asymptotics.

    PubMed

    Ablowitz, Mark J; Baldwin, Douglas E

    2013-02-01

    Dispersive shock waves (DSWs) are physically important phenomena that occur in systems dominated by weak dispersion and weak nonlinearity. The Korteweg-de Vries (KdV) equation is the universal model for systems with weak dispersion and weak, quadratic nonlinearity. Here we show that the long-time-asymptotic solution of the KdV equation for general, steplike data is a single-phase DSW; this DSW is the "largest" possible DSW based on the boundary data. We find this asymptotic solution using the inverse scattering transform and matched-asymptotic expansions. So while multistep data evolve to have multiphase dynamics at intermediate times, these interacting DSWs eventually merge to form a single-phase DSW at large time. PMID:23496590

  18. Asymptotic structure of hydromagnetically driven relativistic winds

    NASA Technical Reports Server (NTRS)

    Chiueh, Tzihong; Li, Zhi-Yun; Begelman, Mitchell C.

    1991-01-01

    A fully relativistic analysis has been performed of the asymptotic structure of stationary axisymmetric hydromagnetic winds. If a flow fills the region containing the rotation axis, then the flux surfaces in the flow must collimate to a set of current-carrying cylindrical surface extending to infinite transverse radius, collimate to a set of cylindrical surfaces extending to a finite radius, or collimate to a current-free paraboloidal field configuration which fills up the entire space. If an asymptotically cylindrical flow carries a finite current at radii well beyond the light cylinder, then the Lorentz factor of the terminal flow speed on a given flux surface is proportional to the total current enclosed within this flux surface. If a flow is of type II paraboloidal, then its asymptotic energy flux is carried entirely by the gas motion rather than the electromagnetic fields.

  19. Hydrodynamic simulations of the interaction between giant stars and planets

    NASA Astrophysics Data System (ADS)

    Staff, Jan E.; De Marco, Orsola; Wood, Peter; Galaviz, Pablo; Passy, Jean-Claude

    2016-05-01

    We present the results of hydrodynamic simulations of the interaction between a 10 Jupiter mass planet and a red or asymptotic giant branch stars, both with a zero-age main sequence mass of 3.5 M⊙. Dynamic in-spiral time-scales are of the order of few years and a few decades for the red and asymptotic giant branch stars, respectively. The planets will eventually be destroyed at a separation from the core of the giants smaller than the resolution of our simulations, either through evaporation or tidal disruption. As the planets in-spiral, the giant stars' envelopes are somewhat puffed up. Based on relatively long time-scales and even considering the fact that further in-spiral should take place before the planets are destroyed, we predict that the merger would be difficult to observe, with only a relatively small, slow brightening. Very little mass is unbound in the process. These conclusions may change if the planet's orbit enhances the star's main pulsation modes. Based on the angular momentum transfer, we also suspect that this star-planet interaction may be unable to lead to large-scale outflows via the rotation-mediated dynamo effect of Nordhaus and Blackman. Detectable pollution from the destroyed planets would only result for the lightest, lowest metallicity stars. We furthermore find that in both simulations the planets move through the outer stellar envelopes at Mach-3 to Mach-5, reaching Mach-1 towards the end of the simulations. The gravitational drag force decreases and the in-spiral slows down at the sonic transition, as predicted analytically.

  20. Asymptotics of a horizontal liquid bridge

    NASA Astrophysics Data System (ADS)

    Haynes, M.; O'Brien, S. B. G.; Benilov, E. S.

    2016-04-01

    This paper uses asymptotic techniques to find the shape of a two dimensional liquid bridge suspended between two vertical walls. We model the equilibrium bridge shape using the Laplace-Young equation. We use the Bond number as a small parameter to deduce an asymptotic solution which is then compared with numerical solutions. The perturbation approach demonstrates that equilibrium is only possible if the contact angle lies within a hysteresis interval and the analysis relates the width of this interval to the Bond number. This result is verified by comparison with a global force balance. In addition, we examine the quasi-static evolution of such a two dimensional bridge.

  1. Asymptotic behavior of degenerate logistic equations

    NASA Astrophysics Data System (ADS)

    Arrieta, José M.; Pardo, Rosa; Rodríguez-Bernal, Aníbal

    2015-12-01

    We analyze the asymptotic behavior of positive solutions of parabolic equations with a class of degenerate logistic nonlinearities of the type λu - n (x)uρ. An important characteristic of this work is that the region where the logistic term n (ṡ) vanishes, that is K0 = { x : n (x) = 0 }, may be non-smooth. We analyze conditions on λ, ρ, n (ṡ) and K0 guaranteeing that the solution starting at a positive initial condition remains bounded or blows up as time goes to infinity. The asymptotic behavior may not be the same in different parts of K0.

  2. Electroluminescence of Giant Stretchability.

    PubMed

    Yang, Can Hui; Chen, Baohong; Zhou, Jinxiong; Chen, Yong Mei; Suo, Zhigang

    2016-06-01

    A new type of electroluminescent device achieves giant stretchability by integrating electronic and ionic components. The device uses phosphor powders as electroluminescent materials, and hydrogels as stretchable and transparent ionic conductors. Subject to cyclic voltage, the phosphor powders luminesce, but the ionic conductors do not electrolyze. The device produces constant luminance when stretched up to an area strain of 1500%. PMID:26610277

  3. A giant ureteric calculus

    PubMed Central

    Rathod, Rajiv; Bansal, Prashant; Gutta, Srinivas

    2013-01-01

    Ureteric stones are usually small and symptomatic. We present a case of a 35-year old female who presented with minimally symptomatic right distal ureteric calculus with proximal hydroureteronephrosis. Laparoscopic right ureterolithotomy was performed and a giant ureteric calculus measuring 11 cm Χ 1.5 cm, weighing 40 g was retrieved. PMID:24082453

  4. Giant urethral calculus

    PubMed Central

    Kotkar, Kunal; Thakkar, Ravi; Songra, MC

    2011-01-01

    Primary urethral calculus is rarely seen and is usually encountered in men with urethral stricture or diverticulum. We present a case of giant urethral calculus secondary to a urethral stricture in a man. The patient was treated with calculus extraction with end to end urethroplasty. PMID:24950400

  5. Juvenile giant fibroadenoma

    PubMed Central

    Yagnik, Vipul D.

    2011-01-01

    Fibroadenomas are benign solid tumor associated with aberration of normal lobular development. Juvenile giant fibroadenoma is usually single and >5 cm in size /or >500 gms in weight. Important differential diagnoses are: phyllodes tumor and juvenile gigantomastia. Simple excision is the treatment of choice. PMID:24765310

  6. A giant ureteric calculus.

    PubMed

    Rathod, Rajiv; Bansal, Prashant; Gutta, Srinivas

    2013-07-01

    Ureteric stones are usually small and symptomatic. We present a case of a 35-year old female who presented with minimally symptomatic right distal ureteric calculus with proximal hydroureteronephrosis. Laparoscopic right ureterolithotomy was performed and a giant ureteric calculus measuring 11 cm Χ 1.5 cm, weighing 40 g was retrieved. PMID:24082453

  7. METAL-POOR LITHIUM-RICH GIANTS IN THE RADIAL VELOCITY EXPERIMENT SURVEY

    SciTech Connect

    Ruchti, Gregory R.; Fulbright, Jon P.; Wyse, Rosemary F. G.; Gilmore, Gerard F.; Grebel, Eva K.; Bienayme, Olivier; Siebert, Arnaud; Bland-Hawthorn, Joss; Freeman, Ken C.; Gibson, Brad K.; Munari, Ulisse; Navarro, Julio F.; Parker, Quentin A.; Watson, Fred G.; Reid, Warren; Seabroke, George M.; Siviero, Alessandro; Steinmetz, Matthias; Williams, Mary; Zwitter, Tomaz

    2011-12-20

    We report the discovery of eight lithium-rich field giants found in a high-resolution spectroscopic sample of over 700 metal-poor stars ([Fe/H] < -0.5) selected from the Radial Velocity Experiment survey. The majority of the Li-rich giants in our sample are very metal-poor ([Fe/H] {approx}< -1.9), and have a Li abundance (in the form of {sup 7}Li), A(Li) = log (n(Li)/n(H)) + 12, between 2.30 and 3.63, well above the typical upper red giant branch (RGB) limit, A(Li) < 0.5, while two stars, with A(Li) {approx} 1.7-1.8, show similar lithium abundances to normal giants at the same gravity. We further included two metal-poor, Li-rich globular cluster giants in our sample, namely the previously discovered M3-IV101 and newly discovered (in this work) M68-A96. This comprises the largest sample of metal-poor Li-rich giants to date. We performed a detailed abundance analysis of all stars, finding that the majority of our sample stars have elemental abundances similar to that of Li-normal halo giants. Although the evolutionary phase of each Li-rich giant cannot be definitively determined, the Li-rich phase is likely connected to extra mixing at the RGB bump or early asymptotic giant branch that triggers cool bottom processing in which the bottom of the outer convective envelope is connected to the H-burning shell in the star. The surface of a star becomes Li-enhanced as {sup 7}Be (which burns to {sup 7}Li) is transported to the stellar surface via the Cameron-Fowler mechanism. We discuss and discriminate among several models for the extra mixing that can cause Li production, given the detailed abundances of the Li-rich giants in our sample.

  8. 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.

  9. Pulsational variability in proto-planetary nebulae and other post-AGB objects

    NASA Astrophysics Data System (ADS)

    Hrivnak, Bruce J.

    2016-07-01

    Light and velocity curves of several classes of pulsating stars have been successfully modeled to determine physical properties of the stars. In this observational study, we review briefly the pulsational variability of the main classes of post-AGB stars. Our attention is focused in particular on proto-planetary nebulae (PPNe), those in the short-lived phase from AGB stars to the planetary nebulae. New light curves and period analyses have been used to determine the following general properties of the PPNe variability: (a) periods range from 35 to 160 days for those of F—G spectral types, with much shorter periods (< 1 day) found for those of early-B spectral type; (b) there is a correlation between the pulsation period, maximum amplitude, and temperature of the star, with cooler stars pulsating with longer periods and larger amplitudes; (c) similar correlations are found for carbon-rich, oxygen-rich, and lower-metalicity PPNe; and (d) multiple periods are found for all of them, with P2/P1 = 1.0±0.1. New models are needed to exploit these results.

  10. Asymptotic behaviour of backward elastic scattering

    NASA Astrophysics Data System (ADS)

    Germond, J. F.; Lombard, R. J.

    1988-05-01

    We discuss a compact formula proposed by Dias de Deus and Pimenta for the asymptotic value of the elastic scattering amplitude at backward angles. Improvements and generalization are obtained by means of the saddle-point method which corroborate old calculations by Serber.

  11. Exponential asymptotics of the Voigt functions

    NASA Astrophysics Data System (ADS)

    Paris, R. B.

    2015-06-01

    We obtain the asymptotic expansion of the Voigt functionss K( x, y) and L( x, y) for large (real) values of the variables x and y, paying particular attention to the exponentially small contributions. A Stokes phenomenon is encountered as with x > 0 fixed. Numerical examples are presented to demonstrate the accuracy of these new expansions.

  12. Lectures on renormalization and asymptotic safety

    SciTech Connect

    Nagy, Sandor

    2014-11-15

    A short introduction is given on the functional renormalization group method, putting emphasis on its nonperturbative aspects. The method enables to find nontrivial fixed points in quantum field theoretic models which make them free from divergences and leads to the concept of asymptotic safety. It can be considered as a generalization of the asymptotic freedom which plays a key role in the perturbative renormalization. We summarize and give a short discussion of some important models, which are asymptotically safe such as the Gross–Neveu model, the nonlinear σ model, the sine–Gordon model, and we consider the model of quantum Einstein gravity which seems to show asymptotic safety, too. We also give a detailed analysis of infrared behavior of such scalar models where a spontaneous symmetry breaking takes place. The deep infrared behavior of the broken phase cannot be treated within the framework of perturbative calculations. We demonstrate that there exists an infrared fixed point in the broken phase which creates a new scaling regime there, however its structure is hidden by the singularity of the renormalization group equations. The theory spaces of these models show several similar properties, namely the models have the same phase and fixed point structure. The quantum Einstein gravity also exhibits similarities when considering the global aspects of its theory space since the appearing two phases there show analogies with the symmetric and the broken phases of the scalar models. These results be nicely uncovered by the functional renormalization group method.

  13. Asymptotic theory of relativistic, magnetized jets

    SciTech Connect

    Lyubarsky, Yuri

    2011-01-15

    The structure of a relativistically hot, strongly magnetized jet is investigated at large distances from the source. Asymptotic equations are derived describing collimation and acceleration of the externally confined jet. Conditions are found for the transformation of the thermal energy into the fluid kinetic energy or into the Poynting flux. Simple scalings are presented for the jet collimation angle and Lorentz factors.

  14. Layer tracking, asymptotics, and domain decomposition

    NASA Technical Reports Server (NTRS)

    Brown, D. L.; Chin, R. C. Y.; Hedstrom, G. W.; Manteuffel, T. A.

    1991-01-01

    A preliminary report is presented on the work on the tracking of internal layers in a singularly-perturbed convection-diffusion equation. It is shown why such tracking may be desirable, and it is also shown how to do it using domain decomposition based on asymptotic analysis.

  15. Eigenvalue asymptotics for Dirac-Bessel operators

    NASA Astrophysics Data System (ADS)

    Hryniv, Rostyslav O.; Mykytyuk, Yaroslav V.

    2016-06-01

    In this paper, we establish the eigenvalue asymptotics for non-self-adjoint Dirac-Bessel operators on (0, 1) with arbitrary real angular momenta and square integrable potentials, which gives the first step for solution of the related inverse problem. The approach is based on a careful examination of the corresponding characteristic functions and their zero distribution.

  16. Uncertainties on near-core mixing in red-clump stars: effects on the period spacing and on the luminosity of the AGB bump

    NASA Astrophysics Data System (ADS)

    Bossini, Diego; Miglio, Andrea; Salaris, Maurizio; Pietrinferni, Adriano; Montalbán, Josefina; Bressan, Alessandro; Noels, Arlette; Cassisi, Santi; Girardi, Léo; Marigo, Paola

    2015-11-01

    Low-mass stars in the He-core-burning (HeCB) phase play a major role in stellar, galactic, and extragalactic astrophysics. The ability to predict accurately the properties of these stars, however, depends on our understanding of convection, which remains one of the key open questions in stellar modelling. We argue that the combination of the luminosity of the AGB bump (AGBb) and the period spacing of gravity modes (ΔΠ1) during the HeCB phase provides us with a decisive test to discriminate between competing models of these stars. We use the Modules for Experiments in Stellar Astrophysics (MESA), a Bag of Stellar Tracks and Isochrones (BaSTI), and PAdova & TRieste Stellar Evolution Code (PARSEC) stellar evolution codes to model a typical giant star observed by Kepler. We explore how various near-core-mixing scenarios affect the predictions of the above-mentioned constraints, and we find that ΔΠ1 depends strongly on the prescription adopted. Moreover we show that the detailed behaviour of ΔΠ1 shows the signature of sharp variations in the Brunt-Väisälä frequency, which could potentially give additional information about near-core features. We find evidence for the AGBb among Kepler targets, and a first comparison with observations shows that, even if standard models are able to reproduce the luminosity distribution, no standard model can account for satisfactorily the period spacing of HeCB stars. Our analysis allows us to outline a candidate model to describe simultaneously the two observed distributions: a model with a moderate overshooting region characterized by an adiabatic thermal stratification. This prescription will be tested in the future on cluster stars, to limit possible observational biases.

  17. Massive Open Online Courses (MOOCs): A Primer for University and College Board Members. An AGB White Paper

    ERIC Educational Resources Information Center

    Voss, Brian D.

    2013-01-01

    The environment in which MOOCs and other forms of online education operate is changing virtually every day. Based upon a presentation given to the board of directors of AGB, this white paper is an effort to give board chairs, presidents, and others some context to help guide discussions on their own campuses. It provides a primer on MOOCs,…

  18. A G-Protein β Subunit, AGB1, Negatively Regulates the ABA Response and Drought Tolerance by Down-Regulating AtMPK6-Related Pathway in Arabidopsis

    PubMed Central

    Xu, Dong-bei; Chen, Ming; Ma, Ya-nan; Xu, Zhao-shi; Li, Lian-cheng; Chen, Yao-feng; Ma, You-zhi

    2015-01-01

    Heterotrimeric G-proteins are versatile regulators involved in diverse cellular processes in eukaryotes. In plants, the function of G-proteins is primarily associated with ABA signaling. However, the downstream effectors and the molecular mechanisms in the ABA pathway remain largely unknown. In this study, an AGB1 mutant (agb1-2) was found to show enhanced drought tolerance, indicating that AGB1 might negatively regulate drought tolerance in Arabidopsis. Data showed that AGB1 interacted with protein kinase AtMPK6 that was previously shown to phosphorylate AtVIP1, a transcription factor responding to ABA signaling. Our study found that transcript levels of three ABA responsive genes, AtMPK6, AtVIP1 and AtMYB44 (downstream gene of AtVIP1), were significantly up-regulated in agb1-2 lines after ABA or drought treatments. Other ABA-responsive and drought-inducible genes, such as RD29A (downstream gene of AtMYB44), were also up-regulated in agb1-2 lines. Furthermore, overexpression of AtVIP1 resulted in hypersensitivity to ABA at seed germination and seedling stages, and significantly enhanced drought tolerance in transgenic plants. These results suggest that AGB1 was involved in the ABA signaling pathway and drought tolerance in Arabidopsis through down-regulating the AtMPK6, AtVIP1 and AtMYB44 cascade. PMID:25635681

  19. Asymptotic coefficients for one-interacting-level Voigt profiles

    NASA Astrophysics Data System (ADS)

    Cope, D.; Lovett, R. J.

    1988-02-01

    The asymptotic behavior of general Voigt profiles with general width and shift functions has been determined by Cope and Lovett (1987). The resulting asymptotic coefficients are functions of the perturber/radiator mass ratio; also, the coefficients for the one-interacting-level (OIL) profiles proposed by Ward et al. (1974) were studied. In this paper, the behavior of the OIL asymptotic coefficients for large mass ratio values is determined, thereby providing a complete picture of OIL asymptotics for all mass ratios.

  20. A giant vesical calculus.

    PubMed

    Rahman, M; Uddin, A; Das, G C; Akanda, N I

    2007-07-01

    Massive or giant vesical calculus is a rare entity in the recent urological practice. Males are affected more than the females. Vesical calculi are usually secondary to bladder outlet obstruction. These patients present with recurrent urinary tract infection, haematuria or with retention of urine. We report a young male patient who presented with defaecatory problems along with other urinary symptoms. The patient having an average built, non diabetic but hypertensive. The stone could be palpated by physical examination. His urea levels were within normal limits but urine examination shows infection. USG reveals bilateral hydronephrosis with multiple stones in both kidneys along with a giant vesical calculus. After controlling urinary infection and hypertention he underwent an open cystolithotomy. During operation digital rectal help was needed to remove the stone as it was adherent with bladder mucosa. Post operative period was uneventful. His urinary output was quite normal and had no defaecatory problems. Patient left the hospital 10 days after operation. PMID:17917633

  1. Ice Giant Exploration

    NASA Astrophysics Data System (ADS)

    Rymer, A. M.; Arridge, C. S.; Masters, A.; Turtle, E. P.; Simon, A. A.; Hofstadter, M. D.; Turrini, D.; Politi, R.

    2015-12-01

    The Ice Giants in our solar system, Uranus and Neptune, are fundamentally different from their Gas Giant siblings Jupiter and Saturn, from the different proportions of rock and ice to the configuration of their planetary magnetic fields. Kepler space telescope discoveries of exo-planets indicate that planets of this type are among the most ubiquitous universally and therefore a future mission to explore the nature of the Ice Giants in our own solar system will provide insights into the nature of extra-solar system objects in general. Uranus has the smallest self- luminosity of all the planets, potentially related to catastrophic events early in the planet's history, which also may explain Uranus' large obliquity. Uranus' atmosphere is subject to extreme seasonal forcing making it unique in the Solar System. Neptune is also unique in a number of ways, notably its large moon Triton which is likely a captured Kuiper Belt Object and one of only two moons in the solar system with a robustly collisional atmosphere. Similar to Uranus, the angle between the solar wind and the magnetic dipole axis is subject to large-amplitude variations on both diurnal and seasonal timescales, but peculiarly it has one of the quietest magnetospheres of the solar system, at least according to Voyager 2, the only spacecraft to encounter Neptune to date. A comprehensive mission, as advocated in the Decadal Survey, would provide enormous science return but is also challenging and expensive. In this presentation we will discuss mission scenarios and suggest how collaboration between disciplines and internationally can help us to pursue a mission that includes Ice Giant exploration.

  2. Giant thymic carcinoid.

    PubMed

    John, L C; Hornick, P; Lang, S; Wallis, J; Edmondson, S J

    1991-05-01

    Thymic carcinoid is a rare tumour. It may present with ectopic endocrine secretion or with symptoms of compression as a result of its size. A case is reported which presented with symptoms of compression where the size of the tumour was uniquely large such as to warrant the term giant thymic carcinoid. The typical histological features are described, together with its possible origin and its likely prognosis. PMID:1852667

  3. Giant dedifferentiated retroperitoneal liposarcoma.

    PubMed

    Dominguez, Elias; Lopez de Cenarruzabeitia, Iñigo; Martinez, Manuel; Rueda, J C; Lede, A; Barreiro, Erica; Diz, Susana

    2008-01-01

    Liposarcoma tumors only represent 0.1% of all cancers, but they are the more common of retroperitoneal sarcomas. It has a great tendency for local recurrence, mainly the dedifferentiated variety, but its complete resection can provide a 5-year survival of 70%. In this report, we present a case of a giant dedifferentiated retroperitoneal liposarcoma that did not affect any neighboring organ and that was successfully treated by means of complete surgical resection. PMID:19731863

  4. Giant rodlike reversed micelles

    SciTech Connect

    Yu, Z.J.; Neuman, R.D. )

    1994-05-04

    Herein we report that sodium bis(2-ethylhexyl)phosphate, which is similar in structure to the classical surfactant sodium bis(2-ethylhexyl)sulfosuccinate (AOT), forms very large rodlike reversed micelles and that their size can be even much larger if water is removed from the apolar solution. We further suggest that long-range electrostatic interactions are the primary driving force for the formation of giant reversed micelles. 19 refs., 3 figs.

  5. Giant cell arteritis

    PubMed Central

    Calvo-Romero, J

    2003-01-01

    Giant cell arteritis (GCA), temporal arteritis or Horton's arteritis, is a systemic vasculitis which involves large and medium sized vessels, especially the extracranial branches of the carotid arteries, in persons usually older than 50 years. Permanent visual loss, ischaemic strokes, and thoracic and abdominal aortic aneurysms are feared complications of GCA. The treatment consists of high dose steroids. Mortality, with a correct treatment, in patients with GCA seems to be similar that of controls. PMID:13679546

  6. Red giants seismology

    NASA Astrophysics Data System (ADS)

    Mosser, B.; Samadi, R.; Belkacem, K.

    2013-11-01

    The space-borne missions CoRoT and Kepler are indiscreet. With their asteroseismic programs, they tell us what is hidden deep inside the stars. Waves excited just below the stellar surface travel throughout the stellar interior and unveil many secrets: how old is the star, how big, how massive, how fast (or slow) its core is dancing. This paper intends to paparazze the red giants according to the seismic pictures we have from their interiors.

  7. Giant radio pulses

    NASA Astrophysics Data System (ADS)

    Kondratiev, Vladislav

    Rotation-powered radio pulsars exhibit a remarkably diverse spectrum of variability with characteristic time scales from days and even years (intermittent pulsars) to minutes-seconds (nulling) and (sub-)microseconds. The latter time scales are associated with the phenomenon of giant pulses (GPs) and micropulses. The story of GPs started in 1968, when Staelin and Reifenstein discovered the Crab pulsar through its spectacularly bright radio pulses. To date, only seven pulsars out of more than 2200 are known to show GP emission, namely the pulsars B0531+21, B1937+21, B0540-69, B1821-24, B1957+20, J0218+4232, and B1820-30A. Giant pulses are characterized by large energies (more than ten times of the energy of the average pulse), short durations, power-law energy distribution, specific rotational phase of occurrence, high degree of polarization, and accompanying high-energy radiation. Large energies of GPs and coincidence of their phase of occurrence with peaks of high-energy profiles hint at the same mechanism of radio GP and high-energy emission. The correlation of Crab pulsar GPs with optical, X-ray and gamma-ray photons was studied for the past 20 years, with only radio/optical link confirmed so far. In my talk I will present the summary of the observational evidence of radio GPs and give an overview of theoretical advances on giant-pulse emission mechanism.

  8. Multiple Outflows in the Giant Eruption of a Massive Star

    NASA Astrophysics Data System (ADS)

    Humphreys, Roberta M.; Martin, John C.; Gordon, Michael S.; Jones, Terry J.

    2016-08-01

    The supernova impostor PSN J09132750+7627410 in NGC 2748 reached a maximum luminosity of ≈‑14 mag. It was quickly realized that it was not a true supernova, but another example of a nonterminal giant eruption. PSN J09132750+7627410 is distinguished by multiple P Cygni absorption minima in the Balmer emission lines that correspond to outflow velocities of ‑400, ‑1100, and ‑1600 km s‑1. Multiple outflows have been observed in only a few other objects. In this paper we describe the evolution of the spectrum and the P Cygni profiles for 3 months past maximum, the post-maximum formation of a cool, dense wind, and the identification of a possible progenitor. One of the possible progenitors is an infrared source. Its pre-eruption spectral energy distribution suggests a bolometric luminosity of ‑8.3 mag and a dust temperature of 780 K. If it is the progenitor, it is above the AGB limit, unlike the intermediate-luminosity red transients. The three P Cygni profiles could be due to ejecta from the current eruption, the wind of the progenitor, or previous mass-loss events. We suggest that they were all formed as part of the same high-mass-loss event and are due to material ejected at different velocities or energies. We also suggest that multiple outflows during giant eruptions may be more common than reported. Based on observations obtained with the Large Binocular Telescope (LBT), an international collaboration among institutions in the United States, Italy, and Germany. LBT Corporation partners are the University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; The Ohio State University and The Research Corporation, on behalf of the University of Notre Dame, University of Minnesota, and University of Virginia.

  9. Brane model with two asymptotic regions

    SciTech Connect

    Lubo, Musongela

    2005-02-15

    Some brane models rely on a generalization of the Melvin magnetic universe including a complex scalar field among the sources. We argue that the geometric interpretation of Kip. S. Thorne of this geometry restricts the kind of potential a complex scalar field can display to keep the same asymptotic behavior. While a finite energy is not obtained for a Mexican hat potential in this interpretation, this is the case for a potential displaying a broken phase and an unbroken one. We use for technical simplicity and illustrative purposes an ad hoc potential which however shares some features with those obtained in some supergravity models. We construct a sixth dimensional cylindrically symmetric solution which has two asymptotic regions: the Melvin-like metric on one side and a flat space displaying a conical singularity on the other. The causal structure of the configuration is discussed. Unfortunately, gravity is not localized on the brane.

  10. Brane model with two asymptotic regions

    NASA Astrophysics Data System (ADS)

    Lubo, Musongela

    2005-02-01

    Some brane models rely on a generalization of the Melvin magnetic universe including a complex scalar field among the sources. We argue that the geometric interpretation of Kip. S. Thorne of this geometry restricts the kind of potential a complex scalar field can display to keep the same asymptotic behavior. While a finite energy is not obtained for a Mexican hat potential in this interpretation, this is the case for a potential displaying a broken phase and an unbroken one. We use for technical simplicity and illustrative purposes an ad hoc potential which however shares some features with those obtained in some supergravity models. We construct a sixth dimensional cylindrically symmetric solution which has two asymptotic regions: the Melvin-like metric on one side and a flat space displaying a conical singularity on the other. The causal structure of the configuration is discussed. Unfortunately, gravity is not localized on the brane.

  11. Asymptotics of Determinants of Bessel Operators

    NASA Astrophysics Data System (ADS)

    Basor, Estelle L.; Ehrhardt, Torsten

    For aL∞(+)∩L1(+) the truncated Bessel operator Bτ(a) is the integral operator acting on L2[0,τ] with the kernel where Jν stands for the Bessel function with ν>-1. In this paper we determine the asymptotics of the determinant det(I+Bτ(a)) as τ-->∞ for sufficiently smooth functions a for which a(x)≠1 for all x[0,∞). The asymptotic formula is of the form det(I+Bτ(a)) GτE with certain constants G and E, and thus similar to the well-known Szegö-Akhiezer-Kac formula for truncated Wiener-Hopf determinants.

  12. Unusual Giant Prostatic Urethral Calculus

    PubMed Central

    Bello, A.; Maitama, H. Y.; Mbibu, N. H.; Kalayi, G. D.; Ahmed, A.

    2010-01-01

    Giant vesico-prostatic urethral calculus is uncommon. Urethral stones rarely form primarily in the urethra, and they are usually associated with urethral strictures, posterior urethral valve or diverticula. We report a case of a 32-year-old man with giant vesico-prostatic (collar-stud) urethral stone presenting with sepsis and bladder outlet obstruction. The clinical presentation, management, and outcome of the giant prostatic urethral calculus are reviewed. PMID:22091328

  13. Theoretical spectra of circumstellar dust shells around carbon-rich asymptotic giant branch stars

    NASA Technical Reports Server (NTRS)

    Winters, J. M.; Dominik, C.; Sedlmayr, E.

    1994-01-01

    Realistic modeling of circumstellar dust shells around evolved stars has to include a physical treatment of the interaction among hydrodynamics, thermodynamics, radiative transfer, chemistry and dust formation and -growth. A self-consistent solution of this problem is presented in the case of stationary, spherical symmetric dust-driven winds. The resulting shell structure and the mass-loss rate are completely determined by the three fundamental stellar parameters stellar mass M(stellar), stellar luminosity L(stellar) and effective temperature T(sub eff) and by the element abundances epsilon(sub i). A detailed calculation of the transport coefficients of the dust component by means of the particle size distribution function and the solution of the non-grey radiative transfer problem provide realistic synthetic spectra of the dust shell models. We discuss the dependence of the resulting spectra on the stellar parameters in terms of infrared two color diagrams. Application of these model calculations to the prominent infrared object IRC +10216 yields best agreement with the observed spectrum and the visibility data at maximum light for the stellar parameters M(stellar) = 0.7 solar mass, L(stellar) = 2.4 x 10(exp 4) solar luminosity, T(stellar) = 2010K and a carbon to oxygen ratio of epsilon(sub c)/epsilon(sub o) = 1.40, which corresponds to a mass-loss rate of M-dot = 8 x 10(exp -5) solar mass/yr. In this model only amorphous carbon grains are considered as the main opacity source. From this model a distance to IRC +10216 of d = 170pc is deduced. The total mass contained in the circumstellar dust shell implies and initial main sequence mass of M(sub ZAMS) greater than or = 1.3 solar mass for IRC +10216.

  14. A collimated jet of molecular gas from a star on the asymptotic giant branch.

    PubMed

    Imai, Hiroshi; Obara, Kumiko; Diamond, Philip J; Omodaka, Toshihiro; Sasao, Tetsuo

    2002-06-20

    Evolved stars of about one solar mass are in general spherically symmetric, yet the planetary nebulae that they produce in the next phase of their evolution tend not to exhibit such symmetry. Collimated 'jets' and outflows of material have been observed up to approximately 0.3 parsec from the central stars of planetary nebulae, and precession of those jets has been proposed to explain the observed asymmetries. Moreover, it has recently been shown theoretically that magnetic fields could launch and collimate such jets. Here we report the detection of a collimated and precessing jet of molecular gas that is traced by water-vapour maser spots approximately 500 astronomical units (au) from the star W43A in Aquila. We conclude that the jet is formed in the immediate vicinity of the star, and infer that elongated planetary nebulae are formed by jets during the short period, of less than 1,000 years, when the star makes its transition through the proto-planetary nebula phase to become a planetary nebula. PMID:12075345

  15. 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.

  16. 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.

  17. TRANSMISSION ELECTRON MICROSCOPY OF Al-RICH SILICATE STARDUST FROM ASYMPTOTIC GIANT BRANCH STARS

    SciTech Connect

    Vollmer, Christian; Hoppe, Peter; Brenker, Frank E.

    2013-05-20

    We report on transmission electron microscopy (TEM) investigations of two mineralogically unusual stardust silicates to constrain their circumstellar condensation conditions. Both grains were identified by high spatial resolution nano secondary ion mass spectrometry (NanoSIMS) in the Acfer 094 meteorite, one of the most pristine carbonaceous chondrites available for study. One grain is a highly crystalline, highly refractory (Fe content < 0.5 at%), structurally undisturbed orthopyroxene (MgSiO{sub 3}) with an unusually high Al content (1.8 {+-} 0.5 at%). This is the first TEM documentation of a single crystal pyroxene within the complete stardust silicate data set. We interpret the microstructure and chemistry of this grain as being a direct condensate from a gas of locally non-solar composition (i.e., with a higher-than-solar Al content and most likely also a lower-than-solar Mg/Si ratio) at (near)-equilibrium conditions. From the overabundance of crystalline olivine (six reported grains to date) compared to crystalline pyroxene (only documented as a single crystal in this work) we infer that formation of olivine over pyroxene is favored in circumstellar environments, in agreement with expectations from condensation theory and experiments. The second stardust silicate consists of an amorphous Ca-Si rich material which lacks any crystallinity based on TEM observations in which tiny (<20 nm) hibonite nanocrystallites are embedded. This complex assemblage therefore attests to the fast cooling and rapidly changing chemical environments under which dust grains in circumstellar shells form.

  18. VizieR Online Data Catalog: NGC 2808 AGB and RGB stars Na abundance (Wang+, 2016)

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Primas, F.; Charbonnel, C.; van der Swaelmen, M.; Bono, G.; Chantereau, W.; Zhao, G.

    2016-05-01

    The high-resolution spectra of our sample of AGB and RGB stars in the Galactic globular cluster NGC 2808 were obtained with the high-resolution multi-object spectrograph FLAMES, mounted on ESO/VLT-UT2. A combined mode was used where the brightest five objects was observed with UVES-fibre and the remaining targets with GIRAFFE/Medusa. The basic information of our sample stars are listed in Table 2, including the evolutionary phase, instrument used for observation, coordinates, photometry and barycentric radial velocity. Our Fe abundances were derived from the equivalent widths of Fe lines, while the Na abundances were determined with spectra synthesis. Both FeI and Na abundances have been corrected for the non-LTE effect. In Table 4 we show the derived stellar parameters of our sample stars, and the Na abundances are shown in Table 6. (3 data files).

  19. The detection of heavy metals in the circumstellar envelopes of post-AGB stars

    NASA Astrophysics Data System (ADS)

    Klochkova, V. G.; Panchuk, V. E.

    2016-03-01

    A new kind of peculiarity is discussed: splitting or asymmetry of strong absorption lines in the optical spectra of selected post-AGB stars with carbon envelopes and atmospheres enriched in carbon and s-process heavy metals. This effect is strongest for BaII ions, whose lines can be split into two or three components. Infrared and radio spectroscopy data are used to demonstrate that the individual components of split absorption lines are formed in structured circumstellar envelopes. Thus, this effect reveals efficient enrichment of the envelope in heavy metals synthesized during the star's earlier evolution. The nature of the strong absorption profile (split or asymmetric, number of components) could be related to the morphology and kinematical and chemical properties of the enenvelope.

  20. Optically Visible Post-AGB and Post-RGB Stars in the Magellanic Clouds

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

    We have performed an extensive low-resolution (R ≍ 1300) optical spectral survey with the AAOmega multi-fiber spectrograph mounted on the 3.9-m Anglo Australian telescope, resulting in a clean and complete census of well-characterised post-AGB objects with spectroscopically determined stellar parameters - Teff, log g, [Fe/H] and E(B-V) - spanning a wide range in luminosity in the Small Magellanic Cloud (SMC) and Large Magellanic Cloud (LMC). The known distances to the Magellanic clouds enabled luminosity estimations for all the objects and led to one of the most important results of this survey: the serendipitous discovery of a group of new, low-luminosity, evolved, dusty post-RGB objects in both Clouds. In this paper, we present an overview of this survey and a few important results.

  1. Using JVLA Observations of SiO Masers to Probe the Extended Atmosphere of an AGB Star: W Hydrae

    NASA Astrophysics Data System (ADS)

    Kamieneski, Patrick S.; Matthews, Lynn D.

    2015-01-01

    The Asymptotic Giant Branch star W Hydrae (W Hya) is known to be a strong source of silicon monoxide (SiO) masers in its extended atmosphere. Jansky Very Large Array imaging observations obtained in February 2014 were used to target eleven SiO J=1-0 rotational transitions near 43 GHz. The vibrational ground state (v=0) lines for the 28SiO, 29SiO, and 30SiO isotopologues were successfully detected, as were the v=1,2,3 lines for 28SiO. Non-detections included the v=1,2 transitions for 29SiO and 30SiO, and the v=4 line for 28SiO. We will summarize the relative shape, size, and intensity of the emission regions of the detected transitions. We have discovered spatially extended ground-state 28SiO emission in a region located approximately 300 to 600 milliarcseconds (projected distance of 34 to 69 AU) from the star. We will discuss a saddle-like distribution and a small gradient in the velocity field for the 28SiO v=1 line, which may help to confirm the existence of a bipolar outflow in W Hya. Additionally, our results indicate that the observed transitions have differing spatial distributions. Peak 28SiO v=1,2,3 emission primarily occupies a region 12 - 42 mas (projected distance of 1.4 - 4.8 AU) west of the star, while the 29SiO and 30SiO isotopologues are located in disparate regions around 45 - 70 mas (5.2 - 8.1 AU) to the northwest of the star.This work was sponsored by a grant from the National Science Foundation Research Experience for Undergraduate program to MIT Haystack Observatory.

  2. Asymptotically flat space–times: an enigma

    NASA Astrophysics Data System (ADS)

    Newman, Ezra T.

    2016-07-01

    We begin by emphasizing that we are dealing with standard Einstein or Einstein–Maxwell theory—absolutely no new physics has been inserted. The fresh item is that the well-known asymptotically flat solutions of the Einstein–Maxwell theory are transformed to a new coordinate system with surprising and (seemingly) inexplicable results. We begin with the standard description of (Null) asymptotically flat space–times described in conventional Bondi-coordinates. After transforming the variables (mainly the asymptotic Weyl tensor components) to a very special set of Newman-Unti (NU) coordinates, we find a series of relations totally mimicking standard Newtonian classical mechanics and Maxwell theory. The surprising and troubling aspect of these relations is that the associated motion and radiation does not take place in physical space–time. Instead these relations takes place in an unusual inherited complex four-dimensional manifold referred to as H-space that has no immediate relationship with space–time. In fact these relations appear in two such spaces, H-space and its dual space \\bar{H}.

  3. Asymptotic modal analysis and statistical energy analysis

    NASA Technical Reports Server (NTRS)

    Dowell, Earl H.

    1988-01-01

    Statistical Energy Analysis (SEA) is defined by considering the asymptotic limit of Classical Modal Analysis, an approach called Asymptotic Modal Analysis (AMA). The general approach is described for both structural and acoustical systems. The theoretical foundation is presented for structural systems, and experimental verification is presented for a structural plate responding to a random force. Work accomplished subsequent to the grant initiation focusses on the acoustic response of an interior cavity (i.e., an aircraft or spacecraft fuselage) with a portion of the wall vibrating in a large number of structural modes. First results were presented at the ASME Winter Annual Meeting in December, 1987, and accepted for publication in the Journal of Vibration, Acoustics, Stress and Reliability in Design. It is shown that asymptotically as the number of acoustic modes excited becomes large, the pressure level in the cavity becomes uniform except at the cavity boundaries. However, the mean square pressure at the cavity corner, edge and wall is, respectively, 8, 4, and 2 times the value in the cavity interior. Also it is shown that when the portion of the wall which is vibrating is near a cavity corner or edge, the response is significantly higher.

  4. Asymptotic dynamics of the exceptional Bianchi cosmologies

    NASA Astrophysics Data System (ADS)

    Hewitt, C. G.; Horwood, J. T.; Wainwright, J.

    2003-05-01

    In this paper we give, for the first time, a qualitative description of the asymptotic dynamics of a class of non-tilted spatially homogeneous (SH) cosmologies, the so-called exceptional Bianchi cosmologies, which are of Bianchi type VI$_{-1/9}$. This class is of interest for two reasons. Firstly, it is generic within the class of non-tilted SH cosmologies, being of the same generality as the models of Bianchi types VIII and IX. Secondly, it is the SH limit of a generic class of spatially inhomogeneous $G_{2}$ cosmologies. Using the orthonormal frame formalism and Hubble-normalized variables, we show that the exceptional Bianchi cosmologies differ from the non-exceptional Bianchi cosmologies of type VI$_{h}$ in two significant ways. Firstly, the models exhibit an oscillatory approach to the initial singularity and hence are not asymptotically self-similar. Secondly, at late times, although the models are asymptotically self-similar, the future attractor for the vacuum-dominated models is the so-called Robinson-Trautman SH model instead of the vacuum SH plane wave models.

  5. 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

  6. IS THE POST-AGB STAR SAO 40039 MILDLY HYDROGEN-DEFICIENT?

    SciTech Connect

    Rao, S. Sumangala; Pandey, Gajendra; Giridhar, Sunetra; Lambert, David L. E-mail: pandey@iiap.res.in E-mail: dll@astro.as.utexas.edu

    2011-08-10

    We have conducted an LTE abundance analysis for SAO 40039, a warm post-AGB star whose spectrum is known to show surprisingly strong He I lines for its effective temperature and has been suspected of being H-deficient and He-rich. High-resolution optical spectra are analyzed using a family of model atmospheres with different He/H ratios. Atmospheric parameters are estimated from the ionization equilibrium set by neutral and singly ionized species of Fe and Mg, the excitation of Fe I and Fe II lines, and the wings of the Paschen lines. On the assumption that the He I lines are of photospheric and not chromospheric origin, a He/H ratio of approximately unity is found by imposing the condition that the adopted He/H ratio of the model atmosphere must equal the ratio derived from the observed He I triplet lines at 5876, 4471, and 4713 A, and singlet lines at 4922 and 5015 A. Using the model with the best-fitting atmospheric parameters for this He/H ratio, SAO 40039 is confirmed to exhibit mild dust-gas depletion, i.e., the star has an atmosphere deficient in elements of high condensation temperature. The star appears to be moderately metal-deficient with [Fe/H] = -0.4 dex. But the star's intrinsic metallicity as estimated from Na, S, and Zn, elements of a low condensation temperature, is [Fe/H]{sub o} {approx_equal} -0.2 ([Fe/H]{sub o} refers to the star's intrinsic metallicity). The star is enriched in N and perhaps O as well, changes reflecting the star's AGB past and the event that led to He enrichment.

  7. The carbon star adventure: modelling atmospheres of a set of C-rich AGB stars

    NASA Astrophysics Data System (ADS)

    Rau, Gioia; Paladini, Claudia; Hron, Josef; Aringer, Bernard; Erikssonn, Kjell; Groenewegen, Martin

    2015-08-01

    We study the atmospheres of a set of carbon rich AGB stars to improve our understanding of the dynamic processes happening in there.For the first time we compare in a systematic way spectrometric, photometric and mid-infrared (VLTI/MIDI) interferometric measurements with different type of model atmospheres: (1) hydrostatic models + MOD-dusty models (Groenewegen, 2012) added a posteriori; (2) self-consistent dynamic model atmospheres (Eriksson et al. 2014). These allow to interpret in a coherent way the dynamic behavior of gas and dust. In addition, the geometric model fitting tool for interferometric data GEM-FIND is applied to carry out a first interpretation of the structural environment of the stars.The results underline that the joint use of different kind of observations, as photometry, spectroscopy and interferometry, is essential for understanding and modeling the atmosphere of pulsating C-rich AGB stars. For our first target, the carbon-rich Mira star RU Vir, the dynamic model atmospheres fit well the ISO/SWS spectra in the wavelength range λ = [2.9, 13.0] μm. However, the object turned out to be “peculiar”: we notice a discrepancy in the visible part of the SED, and in the visibilities. Possible causes are intra/inter-cycle variations in the dynamic model atmospheres, and an eventual presence of a companion star and/or disk or clumps in the atmosphere of RU Vir (Rau et al. subm.). Results on further targets will also be presented.The increased sample of C-rich stars of this work provides crucial constraints for the atmospheric structure and the formation of SiC. Moreover the second generation VLTI instrument MATISSE will be a perfect tool to detect and study asymmetries, as it will allow interferometric imaging in the L, M, and N bands.

  8. Asymptotic form of the Kohn-Sham correlation potential

    SciTech Connect

    Joubert, D. P.

    2007-07-15

    The density-functional correlation potential of a finite system is shown to asymptotically approach a nonzero constant along a nodal surface of the energetically highest occupied orbital and zero everywhere else. This nonuniform asymptotic form of the correlation potential exactly cancels the nonuniform asymptotic behavior of the exact exchange potential discussed by Della Sala and Goerling [Phys. Rev. Lett. 89, 33003 (2002)]. The sum of the exchange and correlation potentials therefore asymptotically tends to -1/r everywhere, consistent with the asymptotic form of the Kohn-Sham potential as analyzed by Almbladh and von Barth [Phys. Rev. B 31, 3231 (1985)].

  9. The light curve shapes as a key to resolving the origin of long secondary periods in red giant stars

    SciTech Connect

    Soszyński, I.; Udalski, A. E-mail: udalski@astrouw.edu.pl

    2014-06-10

    We present a study of Optical Gravitational Lensing Experiment light curves of red giant stars exhibiting long secondary periods (LSPs)—an enigmatic phenomenon commonly observed in stars on the upper red giant branch and asymptotic giant branch. We show that the light curves of LSP stars are essentially identical to those of the spotted variables with one dark spot on their photospheres. Such behavior can be explained by the presence of a dusty cloud orbiting the red giant together with a low-mass companion in a close, circular orbit. We argue that the binary scenario is in agreement with most of the observational properties of LSP variables, including non-sinusoidal shapes of their radial velocity curves.

  10. FLUORINE ABUNDANCES OF GALACTIC LOW-METALLICITY GIANTS

    SciTech Connect

    Li, H. N.; Zhao, G.; Ludwig, H.-G.; Caffau, E.; Christlieb, N. E-mail: gzhao@nao.cas.cn E-mail: ecaffau@lsw.uni-heidelberg.de

    2013-03-01

    With abundances and 2{sigma} upper limits of fluorine (F) in seven metal-poor field giants, nucleosynthesis of stellar F at low metallicity is discussed. The measurements are derived from the HF(1-0) R9 line at 23358 A using near-infrared K-band high-resolution spectra obtained with CRIRES at the Very Large Telescope. The sample reaches lower metallicities than previous studies on F of field giants, ranging from [Fe/H] = -1.56 down to -2.13. Effects of three-dimensional model atmospheres on the derived F and O abundances are quantitatively estimated and shown to be insignificant for the program stars. The observed F yield in the form of [F/O] is compared with two sets of Galactic chemical evolution models, which quantitatively demonstrate the contribution of Type II supernova (SN II) {nu}-process and asymptotic giant branch/Wolf-Rayet stars. It is found that at this low-metallicity region, models cannot well predict the observed distribution of [F/O], while the observations are better fit by models considering an SN II {nu}-process with a neutrino energy of E {sub {nu}} = 3 Multiplication-Sign 10{sup 53} erg. Our sample contains HD 110281, a retrograde orbiting low-{alpha} halo star, showing a similar F evolution as globular clusters. This supports the theory that such halo stars are possibly accreted from dwarf galaxy progenitors of globular clusters in the halo.

  11. 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

  12. Giant Coulomb blockade magnetoresistance

    SciTech Connect

    Zhang, Xiaoguang; Wen, Z. C.; Wei, H. X.; Han, Prof. X. F.

    2010-01-01

    We show that the Coulomb blockade voltage can be made to depend strongly on the electron spin in a thin magnetic granular layer inserted in the middle of an insulating layer of a tunnel junction. This strong spin dependence is predicted from the spin-dependent inter-granular conductance through any of the following effects within the granular layer, giant magnetoresistance (GMR), tunneling magnetoresistance (TMR), colossal magnetoresistance (CMR), or GMR through a polymer spacer. The resulting Coulomb blockade magnetoresistance (CBMR) ratio can exceed the magnetoresistance ratio of the granular layer itself by orders of magnitude. Unlike other magenetoresistance effects, the CBMR effect does not require magnetic electrodes.

  13. Giant Cardiac Cavernous Hemangioma.

    PubMed

    Unger, Eric; Costic, Joseph; Laub, Glenn

    2015-07-01

    We report the case of an asymptomatic giant cardiac cavernous hemangioma in a 71-year-old man. The intracardiac mass was discovered incidentally during surveillance for his prostate cancer; however, the patient initially declined intervention. On presentation to our institution 7 years later, the lesion had enlarged significantly, and the patient consented to excision. At surgery, an 8 × 6.5 × 4.8 cm intracardiac mass located on the inferior heart border was excised with an intact capsule through a median sternotomy approach. The patient had an uneventful postoperative course. We discuss the diagnostic workup, treatment, and characteristics of this rare cardiac tumor. PMID:26140782

  14. The effect of NaCl on stomatal opening in Arabidopsis wild type and agb1 heterotrimeric G-protein mutant plants.

    PubMed

    Yu, Yunqing; Assmann, Sarah M

    2016-01-01

    Salinity is a major agricultural problem that affects crop yield. Na(+) is transported to the shoot through the transpiration stream. The mutant of the sole Arabidopsis heterotrimeric G protein β subunit, agb1, is hypersensitive to salinity in part due to a higher transpiration rate. Here, we investigated the direct effect of Na(+) on stomatal opening using detached epidermal peels of wild type and agb1 plants. In both genotypes, NaCl is equally as effective as KCl in mediating stomatal opening at the concentrations tested. In both genotypes, ABA is less effective in inhibiting Na(+) mediated stomatal opening than K(+) mediated stomatal opening. The agb1 mutant is hyposensitive to ABA inhibition of K(+)-mediated but not Na(+)-mediated stomatal opening. These results suggest that the greater transpiration observed in agb1 plants grown in saline conditions is likely not mediated by differential genotypic direct effects of Na(+) on stomatal apertures. PMID:26431457

  15. The effect of NaCl on stomatal opening in Arabidopsis wild type and agb1 heterotrimeric G-protein mutant plants

    PubMed Central

    Yu, Yunqing; Assmann, Sarah M.

    2016-01-01

    Salinity is a major agricultural problem that affects crop yield. Na+ is transported to the shoot through the transpiration stream. The mutant of the sole Arabidopsis heterotrimeric G protein β subunit, agb1, is hypersensitive to salinity in part due to a higher transpiration rate. Here, we investigated the direct effect of Na+ on stomatal opening using detached epidermal peels of wild type and agb1 plants. In both genotypes, NaCl is equally as effective as KCl in mediating stomatal opening at the concentrations tested. In both genotypes, ABA is less effective in inhibiting Na+ mediated stomatal opening than K+ mediated stomatal opening. The agb1 mutant is hyposensitive to ABA inhibition of K+-mediated but not Na+-mediated stomatal opening. These results suggest that the greater transpiration observed in agb1 plants grown in saline conditions is likely not mediated by differential genotypic direct effects of Na+ on stomatal apertures. PMID:26431457

  16. Construction of space-time ray asymptotics from stationary high-frequency asymptotics in nonstationary problems

    NASA Astrophysics Data System (ADS)

    Plachenov, A. B.

    An algorithm is proposed for the transition from the short-wave asymptotics of stationary problems to the space-time asymptotics of nonstationary problems of linear wave propagation. The relationship between this algorithm and constructs of the spatial-temporal ray tracing method is examined. As an example, the algorithm is applied to the problem of the detection of a diffraction wave in the deep shade behind a smooth convex obstacle in the case where the incident wave is specified by its spatial-temporal ray expansion.

  17. Rheology of giant micelles

    NASA Astrophysics Data System (ADS)

    Cates, M. E.; Fielding, S. M.

    2006-12-01

    Giant micelles are elongated, polymer-like objects created by the self-assembly of amphiphilic molecules (such as detergents) in solution. Giant micelles are typically flexible, and can become highly entangled even at modest concentrations. The resulting viscoelastic solutions show fascinating flow behaviour (rheology) which we address theoretically in this article at two levels. First, we summarize advances in understanding linear viscoelastic spectra and steady-state nonlinear flows, based on microscopic constitutive models that combine the physics of polymer entanglement with the reversible kinetics of self-assembly. Such models were first introduced two decades ago, and since then have been shown to explain robustly several distinctive features of the rheology in the strongly entangled regime, including extreme shear thinning. We then turn to more complex rheological phenomena, particularly involving spatial heterogeneity, spontaneous oscillation, instability and chaos. Recent understanding of these complex flows is based largely on grossly simplified models which capture in outline just a few pertinent microscopic features, such as coupling between stresses and other order parameters such as concentration. The role of ‘structural memory’ (the dependence of structural parameters such as the micellar length distribution on the flow history) in explaining these highly nonlinear phenomena is addressed. Structural memory also plays an intriguing role in the little-understood shear thickening regime, which occurs in a concentration regime close to but below the onset of strong entanglement, and which is marked by a shear-induced transformation from an inviscid to a gelatinous state.

  18. Giant solitary trichoepithelioma

    PubMed Central

    Teli, Bhavuray; Thrishuli, P. B.; Santhosh, R.; Amar, D. N.; Rajpurohit, Shravan

    2015-01-01

    Adnexal tumors like giant solitary trichoepitheliomas are uncommon to most of us to permit a ready familiarity with them. Information regarding the genesis, clinical profile, behavior, and management options for this tumor is limited. There are 18 cases reported in the world literature till date. This review attempts to provide insight to this rare tumor. Our search included indexed literature from Pubmed, Directory of Open Access Journals, Health Inter Network Access to Research Initiative and Google databases in addition to standard dermatology texts. Giant solitary trichoepithelioma is a rare trichogenic tumor with potential for local recurrence. It has predilection for the older age, but may present at any age including at birth. It has close resemblance to basal cell carcinoma and other skin adnexal tumors - clinically, cytologically, and histologically. CD10, CD 34, PHLDA1 but not p75NTR are useful adjunct markers. Surgical excision is the standard treatment. Recurrence and possible transformation into BCC cautions follow up at regular intervals. PMID:25839021

  19. Giant solitary trichoepithelioma.

    PubMed

    Teli, Bhavuray; Thrishuli, P B; Santhosh, R; Amar, D N; Rajpurohit, Shravan

    2015-01-01

    Adnexal tumors like giant solitary trichoepitheliomas are uncommon to most of us to permit a ready familiarity with them. Information regarding the genesis, clinical profile, behavior, and management options for this tumor is limited. There are 18 cases reported in the world literature till date. This review attempts to provide insight to this rare tumor. Our search included indexed literature from Pubmed, Directory of Open Access Journals, Health Inter Network Access to Research Initiative and Google databases in addition to standard dermatology texts. Giant solitary trichoepithelioma is a rare trichogenic tumor with potential for local recurrence. It has predilection for the older age, but may present at any age including at birth. It has close resemblance to basal cell carcinoma and other skin adnexal tumors - clinically, cytologically, and histologically. CD10, CD 34, PHLDA1 but not p75NTR are useful adjunct markers. Surgical excision is the standard treatment. Recurrence and possible transformation into BCC cautions follow up at regular intervals. PMID:25839021

  20. Giant papillary conjunctivitis.

    PubMed Central

    Donshik, P C

    1994-01-01

    Giant papillary conjunctivitis is a syndrome found frequently as a complication of contact lenses. Many variables can affect the onset and severity of the presenting signs and symptoms. Rigid gas permeable contact lenses appear to result in less severe signs and symptoms, with a longer time before the development of giant papillary conjunctivitis. Nonionic, low-water-content soft contact lenses tend to produce less severe signs and symptoms than ionic, low-water-content soft contact lenses. Enzymatic treatment appears to lessen the severity of signs and symptoms. The association of an allergy appears to play a role in the onset of the severity of the signs and symptoms but does not appear to affect the final ability of the individual to wear contact lenses. Using multiple treatment options, such as changing the polymer to a glyceryl methyl methacrylate or a rigid lens, or utilizing a soft lens on a frequent-replacement basis, can result in a success rate of over 90%. In individuals who still have a return of symptoms, the use of topical mast cell stabilizers or a nonsteroidal anti-inflammatory drug as an adjunctive therapy offers the added possibility of keeping these patients in contact lenses. Images FIGURE 1 FIGURE 2 FIGURE 3 FIGURE 4 FIGURE 5 FIGURE 6 FIGURE 7 FIGURE 11 A FIGURE 11 B FIGURE 11 C FIGURE 11 D PMID:7886881

  1. Asymptotic modal analysis and statistical energy analysis

    NASA Technical Reports Server (NTRS)

    Dowell, Earl H.

    1992-01-01

    Asymptotic Modal Analysis (AMA) is a method which is used to model linear dynamical systems with many participating modes. The AMA method was originally developed to show the relationship between statistical energy analysis (SEA) and classical modal analysis (CMA). In the limit of a large number of modes of a vibrating system, the classical modal analysis result can be shown to be equivalent to the statistical energy analysis result. As the CMA result evolves into the SEA result, a number of systematic assumptions are made. Most of these assumptions are based upon the supposition that the number of modes approaches infinity. It is for this reason that the term 'asymptotic' is used. AMA is the asymptotic result of taking the limit of CMA as the number of modes approaches infinity. AMA refers to any of the intermediate results between CMA and SEA, as well as the SEA result which is derived from CMA. The main advantage of the AMA method is that individual modal characteristics are not required in the model or computations. By contrast, CMA requires that each modal parameter be evaluated at each frequency. In the latter, contributions from each mode are computed and the final answer is obtained by summing over all the modes in the particular band of interest. AMA evaluates modal parameters only at their center frequency and does not sum the individual contributions from each mode in order to obtain a final result. The method is similar to SEA in this respect. However, SEA is only capable of obtaining spatial averages or means, as it is a statistical method. Since AMA is systematically derived from CMA, it can obtain local spatial information as well.

  2. Asymptotic symmetries of Yang-Mills theory

    NASA Astrophysics Data System (ADS)

    Strominger, Andrew

    2014-07-01

    Asymptotic symmetries at future null infinity ( +) of Minkowski space for electrodynamics with massless charged fields, as well as nonabelian gauge theories with gauge group G, are considered at the semiclassical level. The possibility of charge/color flux through + suggests the symmetry group is infinite-dimensional. It is conjectured that the symmetries include a G Kac-Moody symmetry whose generators are "large" gauge transformations which approach locally holomorphic functions on the conformal two-sphere at + and are invariant under null translations. The Kac-Moody currents are constructed from the gauge field at the future boundary of +. The current Ward identities include Weinberg's soft photon theorem and its colored extension.

  3. Exact and asymptotic distributions of LULU smoothers

    NASA Astrophysics Data System (ADS)

    Conradie, W. J.; de Wet, T.; Jankowitz, M.

    2006-02-01

    This paper considers a class of non-linear smoothers, called LULU smoothers, introduced by Rohwer in the late eighties in the mathematics literature, and since then investigated fairly extensively by a number of authors for its mathematical properties. They have been successfully applied in various engineering and scientific problems. However, to date their distribution theory has not received any attention in the literature. In this paper we derive their exact as well as asymptotic distributions and show their relationship to the upper order statistics.

  4. Spectroscopy of Six Red Giants in the Draco Dwarf Spheroidal Galaxy

    NASA Astrophysics Data System (ADS)

    Smith, Graeme H.; Siegel, Michael H.; Shetrone, Matthew D.; Winnick, Rebeccah

    2006-10-01

    Keck Observatory LRIS-B (Low Resolution Imaging Spectrometer) spectra are reported for six red giant stars in the Draco dwarf spheroidal galaxy and several comparison giants in the globular cluster M13. Indexes that quantify the strengths of the Ca II H and K lines, the λ3883 and λ4215 CN bands, and the λ4300 G band have been measured. These data confirm evidence of metallicity inhomogeneity within Draco obtained by previous authors. The four brightest giants in the sample have absolute magnitudes in the range -2.6giants and that some giants have higher [C/Fe] ratios than is typical of giants in the globular clusters M13 and M92. Several suggestions are made as to why some Draco stars may have higher [C/Fe] ratios than globular cluster red giants: deep mixing might be inhibited in these Draco stars, they may formerly have been mass-transfer binaries that acquired carbon from a more massive companion, or the Draco dwarf galaxy may have experienced relatively slow chemical evolution over a period of several billion years, allowing carbon-enhanced ejecta from intermediate-mass asymptotic giant branch stars to enrich the interstellar medium while star formation was still occurring. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

  5. Allometry indicates giant eyes of giant squid are not exceptional

    PubMed Central

    2013-01-01

    Background The eyes of giant and colossal squid are among the largest eyes in the history of life. It was recently proposed that sperm whale predation is the main driver of eye size evolution in giant squid, on the basis of an optical model that suggested optimal performance in detecting large luminous visual targets such as whales in the deep sea. However, it is poorly understood how the eye size of giant and colossal squid compares to that of other aquatic organisms when scaling effects are considered. Results We performed a large-scale comparative study that included 87 squid species and 237 species of acanthomorph fish. While squid have larger eyes than most acanthomorphs, a comparison of relative eye size among squid suggests that giant and colossal squid do not have unusually large eyes. After revising constants used in a previous model we found that large eyes perform equally well in detecting point targets and large luminous targets in the deep sea. Conclusions The eyes of giant and colossal squid do not appear exceptionally large when allometric effects are considered. It is probable that the giant eyes of giant squid result from a phylogenetically conserved developmental pattern manifested in very large animals. Whatever the cause of large eyes, they appear to have several advantages for vision in the reduced light of the deep mesopelagic zone. PMID:23418818

  6. 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

  7. 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.

  8. ON ASYMPTOTIC DISTRIBUTION AND ASYMPTOTIC EFFICIENCY OF LEAST SQUARES ESTIMATORS OF SPATIAL VARIOGRAM PARAMETERS. (R827257)

    EPA Science Inventory

    Abstract

    In this article, we consider the least-squares approach for estimating parameters of a spatial variogram and establish consistency and asymptotic normality of these estimators under general conditions. Large-sample distributions are also established under a sp...

  9. 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.

  10. Asymptotic modal analysis and statistical energy analysis

    NASA Technical Reports Server (NTRS)

    Dowell, Earl H.; Peretti, Linda F.

    1990-01-01

    The sound field of a structural-acoustic enclosure was subject to experimental analysis and theoretical description in order to develop an efficient and accurate method for predicting sound pressure levels in enclosures such as aircraft fuselages. Asymptotic Modal Analysis (AMA) is the method under investigation. AMA is derived from classical modal analysis (CMA) by considering the asymptotic limit of the sound pressure level as the number of acoustic and/or structural modes approaches infinity. Using AMA, results identical to those of Statistical Energy Analysis (SEA) were obtained for the spatially-averaged sound pressure levels in the interior. AMA is systematically derived from CMA and therefore the degree of generality of the end result can be adjusted through the choice of appropriate simplifying assumptions. For example, AMA can be used to obtain local sound pressure levels at particular points inside the enclosure, or to include the effects of varying the size and/or location of the sound source. AMA theoretical results were compared with CMA theory and also with experiment for the case where the structural-acoustic enclosure is a rectangular cavity with part of one wall flexible and vibrating, while the rest of the cavity is rigid.

  11. Asymptotically Lifshitz brane-world black holes

    SciTech Connect

    Ranjbar, Arash Sepangi, Hamid Reza Shahidi, Shahab

    2012-12-15

    We study the gravity dual of a Lifshitz field theory in the context of a RSII brane-world scenario, taking into account the effects of the extra dimension through the contribution of the electric part of the Weyl tensor. We study the thermodynamical behavior of such asymptotically Lifshitz black holes. It is shown that the entropy imposes the critical exponent z to be bounded from above. This maximum value of z corresponds to a positive infinite entropy as long as the temperature is kept positive. The stability and phase transition for different spatial topologies are also discussed. - Highlights: Black-Right-Pointing-Pointer Studying the gravity dual of a Lifshitz field theory in the context of brane-world scenario. Black-Right-Pointing-Pointer Studying the thermodynamical behavior of asymptotically Lifshitz black holes. Black-Right-Pointing-Pointer Showing that the entropy imposes the critical exponent z to be bounded from above. Black-Right-Pointing-Pointer Discussing the phase transition for different spatial topologies.

  12. Vacuum polarization in asymptotically Lifshitz black holes

    NASA Astrophysics Data System (ADS)

    Quinta, Gonçalo M.; Flachi, Antonino; Lemos, José P. S.

    2016-06-01

    There has been considerable interest in applying the gauge-gravity duality to condensed matter theories with particular attention being devoted to gravity duals (Lifshitz spacetimes) of theories that exhibit anisotropic scaling. In this context, black hole solutions with Lifshitz asymptotics have also been constructed, focused on incorporating finite temperature effects. The goal here is to look at quantum polarization effects in these spacetimes and, to this aim, we develop a way to compute the coincidence limit of the Green's function for massive, nonminimally coupled scalar fields, adapting to the present situation the analysis developed for the case of asymptotically anti-de Sitter black holes. The basics are similar to previous calculations; however, in the Lifshitz case, one needs to extend the previous results to include a more general form for the metric and dependence on the dynamical exponent. All formulas are shown to reduce to the anti-de Sitter (AdS) case studied before once the value of the dynamical exponent is set to unity and the metric functions are accordingly chosen. The analytical results we present are general and can be applied to a variety of cases, in fact, to all spherically symmetric Lifshitz black hole solutions. We also implement the numerical analysis choosing some known Lifshitz black hole solutions as illustration.

  13. Structural aspects of asymptotically safe black holes

    NASA Astrophysics Data System (ADS)

    Koch, Benjamin; Saueressig, Frank

    2014-01-01

    We study the quantum modifications of classical, spherically symmetric Schwarzschild (anti-) de Sitter black holes within quantum Einstein gravity. The quantum effects are incorporated through the running coupling constants Gk and Λk, computed within the exact renormalization group approach, and a common scale-setting procedure. We find that, in contrast to common intuition, it is actually the cosmological constant that determines the short-distance structure of the RG-improved black hole: in the asymptotic UV the structure of the quantum solutions is universal and given by the classical Schwarzschild-de Sitter solution, entailing a self-similarity between the classical and quantum regime. As a consequence asymptotically safe black holes evaporate completely and no Planck-size remnants are formed. Moreover, the thermodynamic entropy of the critical Nariai black hole is shown to agree with the microstate count based on the effective average action, suggesting that the entropy originates from quantum fluctuations around the mean-field geometry.

  14. Asymptotic role of entanglement in quantum metrology

    NASA Astrophysics Data System (ADS)

    Augusiak, R.; Kołodyński, J.; Streltsov, A.; Bera, M. N.; Acín, A.; Lewenstein, M.

    2016-07-01

    Quantum systems allow one to sense physical parameters beyond the reach of classical statistics—with resolutions greater than 1 /N , where N is the number of constituent particles independently probing a parameter. In the canonical phase-sensing scenario the Heisenberg limit 1 /N2 may be reached, which requires, as we show, both the relative size of the largest entangled block and the geometric measure of entanglement to be nonvanishing as N →∞ . Yet, we also demonstrate that in the asymptotic N limit any precision scaling arbitrarily close to the Heisenberg limit (1 /N2 -ɛ with any ɛ >0 ) may be attained, even though the system gradually becomes noisier and separable, so that both the above entanglement quantifiers asymptotically vanish. Our work shows that sufficiently large quantum systems achieve nearly optimal resolutions despite their relative amount of entanglement being arbitrarily small. In deriving our results, we establish the continuity relation of the quantum Fisher information evaluated for a phaselike parameter, which lets us link it directly to the geometry of quantum states, and hence naturally to the geometric measure of entanglement.

  15. An asymptotic analysis of mixing loss

    SciTech Connect

    Fritsch, G.; Giles, M.B.

    1995-07-01

    The objective of this paper is to establish, in a rigorous mathematical manner, a link between the dissipation of unsteadiness in a two-dimensional compressible flow and the resulting mixing loss. A novel asymptotic approach and a control-volume argument are central to the analysis. It represents the first work clearly identifying the separate contributions to the mixing loss from simultaneous linear disturbances, i.e., from unsteady entropy, vorticity, and pressure waves. The results of the analysis have important implications for numerical simulations of turbomachinery flows; the mixing loss at the stator/rotor interface in steady simulations and numerical smoothing are discussed in depth. For a transonic turbine, the entropy rise through the stage is compared for a steady and an unsteady viscous simulation. The large interface mixing loss in the steady simulation is pointed out and its physical significance is discussed. The asymptotic approach is then applied to the first detailed analysis of interface mixing loss. Contributions from different wave types and wavelengths are quantified and discussed.

  16. Asymptotic accuracy of two-class discrimination

    SciTech Connect

    Ho, T.K.; Baird, H.S.

    1994-12-31

    Poor quality-e.g. sparse or unrepresentative-training data is widely suspected to be one cause of disappointing accuracy of isolated-character classification in modern OCR machines. We conjecture that, for many trainable classification techniques, it is in fact the dominant factor affecting accuracy. To test this, we have carried out a study of the asymptotic accuracy of three dissimilar classifiers on a difficult two-character recognition problem. We state this problem precisely in terms of high-quality prototype images and an explicit model of the distribution of image defects. So stated, the problem can be represented as a stochastic source of an indefinitely long sequence of simulated images labeled with ground truth. Using this sequence, we were able to train all three classifiers to high and statistically indistinguishable asymptotic accuracies (99.9%). This result suggests that the quality of training data was the dominant factor affecting accuracy. The speed of convergence during training, as well as time/space trade-offs during recognition, differed among the classifiers.

  17. Giant magnetostrictive composites

    NASA Astrophysics Data System (ADS)

    Duenas, Terrisa Ann

    The limitation of magnetostrictive composites has been in their low magnetostrictive response when compared to their monolithic counterparts. In this dissertation research is presented describing the methods and analysis used to create a giant magnetostrictive composite (GMC) producing giant strains at low fields, exhibiting magnetization ``jumping'' and the ΔE effect. This composite combines the giant magnetostrictive material, Terfenol-D (Tb0.3Dy0.7Fe2) in particle form, with a nonmetallic binder and is capable of producing strains (at room temperature) exceeding 1000 ppm at a nominal field of 1.5 kOe mechanically unloaded and 1200 ppm at 8 MPa preload (2.5 kOe). Several studies leading to the high response of this composite are presented. A connectivity study shows that a [1-3] connected composite produces 50% more strain than a [0-3] composite. A resin study indicates that the lower the viscosity of the resin, the greater the magnetostrictive response; this is attributed to the removal of voids during degassing. A void study correlates the increase in voids to the decrease in strain response. A model is used to correlate analysis with experimental results within 10% accuracy and shows that an optimal volume fraction exists based on the properties of the binder. Using a Polyscience Spurr low- viscosity (60 cps) binder this volume fraction is nominally 20%; this optimum is attributed to the balance of epoxy contracting on the particle (built-in preload) and the actuation delivered by the magnetostrictive material. In addition to the connectivity, resin, void, and volume-fraction study, particle size and gradation studies are presented. Widely dispersed (<106, <212, <300 μm), narrowly dispersed (<45, (90-106), (275-300) μm), and an optimized bimodal (18.7% of (45-90) μm with 81.3% of (250-300) μm) particle distributions are studied. Results show that the larger the particle size, the higher the magnetostrictive response; this is attributed to the reduction of

  18. 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

  19. 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

  20. Asymptotic behaviour of solutions of semilinear parabolic equations

    SciTech Connect

    Egorov, Yu V; Kondratiev, V A

    2008-04-30

    The asymptotic behaviour of solutions of a second-order semilinear parabolic equation is analyzed in a cylindrical domain that is bounded in the space variables. The dominant term of the asymptotic expansion of the solution as t{yields}+{infinity} is found. It is shown that the solution of this problem is asymptotically equivalent to the solution of a certain non-linear ordinary differential equation. Bibliography: 8 titles.