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Sample records for red galactic agb

  1. 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.

  2. 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

  3. Are Galactic globular cluster AGB stars rich or poor in Sodium?

    NASA Astrophysics Data System (ADS)

    Wang, Yue; Primas, Francesca; Charbonnel, Corinne; Chantereau, William

    2015-08-01

    In recent years, multiple stellar populations have been identified in Galactic globular clusters (GCs),with different scenarios being debated for their origin (e.g., the AGB and the Fast Rotating Massive Stars scenario, which are the most developed in the literature). These populations are currently identified thanks to their chemical properties. In particular stars with sodium overabundances have been found at different evolution stages, from the main sequence turnoff up to the tip of the red giant branch. Surprisingly however, no sodium-rich AGB stars has been found in NGC 6752. This apparent difficulty for stellar evolution could be relieved within the FRMS scenario, which predicts that above a certain cutoff in initial helium and sodium content, stars do miss the AGB.Here we present the results of the chemical analysis of our new AGB star samples observed at the ESO/VLT with FLAMES in three GCs that span a large range in metallicity. Our aim is to investigate which kind of GCs host Na-rich second-generation AGB stars, and to probe the FRMS scenario. We compare the results with theoretical evolution features based on the FRMS model at various metallicities. This study provides a new and original insight onto the GC pollution scenarios.

  4. 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.

  5. 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.

  6. 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

  7. Mass Loss from Dusty AGB and Red Supergiant Stars in the Magellanic Clouds and in the Galaxy

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    Asymptotic giant branch (AGB) and red supergiant (RSG) stars are evolved stars that eject large parts of their mass in outflows of dust and gas. As part of an ongoing effort to measure mass loss from evolved stars in our Galaxy and in the Magellanic Clouds, we are modeling mass loss from AGB and RSG stars in these galaxies. Our approach is twofold. We pursue radiative transfer modeling of the spectral energy distributions (SEDs) of AGB and RSG stars in the Large Magellanic Cloud (LMC), in the Small Magellanic Cloud (SMC), and in the Galactic bulge and in globular clusters of the Milky Way. We are also constructing detailed dust opacity models of AGB and RSG stars in these galaxies for which we have infrared spectra; e.g., from the Spitzer Space Telescope Infrared Spectrograph (IRS). Our sample of infrared spectra largely comes from Spitzer-IRS observations. The detailed dust modeling of spectra informs our choice of dust properties to use in radiative transfer modeling of SEDs. We seek to determine how mass loss from these evolved stars depends upon the metallicity of their host environments. BAS acknowledges funding from NASA ADAP grant NNX15AF15G.

  8. 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.

  9. 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.

  10. 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

  11. 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

  12. Manganese abundances in Galactic bulge red giants

    NASA Astrophysics Data System (ADS)

    Barbuy, B.; Hill, V.; Zoccali, M.; Minniti, D.; Renzini, A.; Ortolani, S.; Gómez, A.; Trevisan, M.; Dutra, N.

    2013-11-01

    Context. Manganese is mainly produced in type II SNe during explosive silicon burning, in incomplete Si-burning regions, and depends on several nucleosynthesis environment conditions, such as mass cut between the matter ejected and falling back onto the remnant, electron and neutron excesses, mixing fallback, and explosion energy. Manganese is also produced in type Ia SNe. Aims: The aim of this work is the study of abundances of the iron-peak element Mn in 56 bulge giants, among which 13 are red clump stars. Four bulge fields along the minor axis are inspected. The study of abundances of Mn-over-Fe as a function of metallicity in the Galactic bulge may shed light on its production mechanisms. Methods: High-resolution spectra were obtained using the FLAMES+UVES spectrograph on the Very Large Telescope. The spectra were obtained within a program to observe 800 stars using the GIRAFFE spectrograph, together with the present UVES spectra. Results: We aim at identifying the chemical evolution of manganese, as a function of metallicity, in the Galactic bulge. We find [Mn/Fe] ~ -0.7 at [Fe/H] ~ -1.3, increasing to a solar value at metallicities close to solar, and showing a spread around - 0.7 ≲ [Fe/H] ≲ -0.2, in good agreement with other work on Mn in bulge stars. There is also good agreement with chemical evolution models. We find no clear difference in the behaviour of the four bulge fields. Whereas [Mn/Fe] vs. [Fe/H] could be identified with the behaviour of the thick disc stars, [Mn/O] vs. [O/H] has a behaviour running parallel, at higher metallicities, compared to thick disc stars, indicating that the bulge enrichment might have proceeded differently from that of the thick disc. Observations collected at the European Southern Observatory, Paranal, Chile (ESO programmes 71.B-0617A, 73.B0074A, and GTO 71.B-0196).Tables 1-6 and Figs. 1-6 are available in electronic form at http://www.aanda.org

  13. VizieR Online Data Catalog: Galactic post-AGB stars distances (Vickers+, 2015)

    NASA Astrophysics Data System (ADS)

    Vickers, S. B.; Frew, D. J.; Parker, Q. A.; Bojicic, I. S.

    2015-07-01

    The Torun catalogue provides easy online access to processed photometric and spectroscopic data for the currently identified Galactic population of PAGB stars and related objects. The catalogue is divided into five categories: (i) very-likely PAGB stars, (ii) RV Tauri stars, (iii) R Coronae Borealis/extreme helium/late thermal pulse stars, (iv) possible PAGB stars and (v) unlikely PAGB objects. Hereafter, likely PAGB stars will be referred to simply as PAGB, R Coronae Borealis/extreme helium/late thermal pulse as R CrB/eHe/LTP, while the possible PAGB objects will be simply referred to as possible. We will present a distance catalogue of the R Tau and R CrB/eHe/LTP stars in a second paper (Vickers et al., in preparation), concentrating on the likely and possible PAGB objects in this work. (3 data files).

  14. 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).

  15. 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

  16. 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.

  17. Millimeter and some near infra-red observations of short-period Miras and other AGB stars

    NASA Astrophysics Data System (ADS)

    Groenewegen, M. A. T.; Baas, F.; Blommaert, J. A. D. L.; Stehle, R.; Josselin, E.; Tilanus, R. P. J.

    1999-12-01

    Millimeter observations of 48 oxygen- and 20 carbon-rich AGB Miras with periods shorter than 400 days are presented. In addition, observations of 14 O-rich and 15 C-stars with longer, or no known, periods have also been obtained. The detection statistics is as follows: in 12CO J=1-0 and 2-1 we observed 97 stars, and detected 66 in at least one line. We find 24 new detections in the 1-0 line, 38 new detections in the 2-1 line, and 29 stars have been detected for the first time in one or both lines. In 12CO J=3-2 we observed 14 stars and detected 11, with 4 new detections. In 13CO J=2-1, 3-2 we observed 2 stars and had one new detection. In HCN(1-0) we observed 5 carbon stars and detected 3, one new. In SO(6_5-5_4) we observed the same 5 stars and detected none. In CS(3-2) we observed 8 carbon stars and detected 3, all new. In SiO(3-2, v=0) we observed 34 O-rich stars and detected 25, all new except one. Near-infrared JHK photometry is presented for seven stars. For four stars it is the first NIR data published. The luminosity and dust mass loss rate are obtained for seven very red stars with unknown pulsation period from modelling the spectral energy distribution (SED) and IRAS LRS spectra. Thereby, a new IR supergiant is confirmed (AFGL 2968). For the rest of the sample, luminosity and distance are obtained in a variety of ways: using hipparcos parallaxes, period-luminosity and period-M_K-relations combined with apparent K magnitudes, and kinematic distances. The dust mass loss rate is obtained from model fitting of the SED (either from the literature, or presented in the present paper), or from the observed IRAS 60 mu m flux, corrected for the photospheric contribution. The gas mass loss rate is derived from the observed CO line intensities, as presented here, combined with existing literature data, if any. This allows the derivation of the dust-to-gas ratio. Our and literature CO J = 3-2 data has been used to calibrate the relation between mass loss rate and peak

  18. Using red clump stars to decompose the galactic magnetic field with distance

    SciTech Connect

    Pavel, Michael D.

    2014-09-01

    A new method for measuring the large-scale structure of the Galactic magnetic field is presented. The Galactic magnetic field has been probed through the Galactic disk with near-infrared starlight polarimetry; however, the distance to each background star is unknown. Using red clump stars as near-infrared standard candles, this work presents the first attempt to decompose the line-of-sight structure of the sky-projected Galactic magnetic field. Two example lines of sight are decomposed: toward a field with many red clump stars and toward a field with few red clump stars. A continuous estimate of magnetic field orientation over several kiloparsecs of distance is possible in the field with many red clump stars, while only discrete estimates are possible in the sparse example. Toward the outer Galaxy, there is a continuous field orientation with distance that shows evidence of perturbation by the Galactic warp. Toward the inner Galaxy, evidence for a large-scale change in the magnetic field geometry is consistent with models of magnetic field reversals, independently derived from Faraday rotation studies. A photo-polarimetric method for identifying candidate intrinsically polarized stars is also presented. The future application of this method to large regions of the sky will begin the process of mapping the Galactic magnetic field in a way never before possible.

  19. 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.

  20. The Galactic Distribution of Massive Star Formation from the Red MSX Source Survey

    NASA Astrophysics Data System (ADS)

    Figura, Charles C.; Urquhart, J. S.

    2013-01-01

    Massive stars inject enormous amounts of energy into their environments in the form of UV radiation and molecular outflows, creating HII regions and enriching local chemistry. These effects provide feedback mechanisms that aid in regulating star formation in the region, and may trigger the formation of subsequent generations of stars. Understanding the mechanics of massive star formation presents an important key to understanding this process and its role in shaping the dynamics of galactic structure. The Red MSX Source (RMS) survey is a multi-wavelength investigation of ~1200 massive young stellar objects (MYSO) and ultra-compact HII (UCHII) regions identified from a sample of colour-selected sources from the Midcourse Space Experiment (MSX) point source catalog and Two Micron All Sky Survey. We present a study of over 900 MYSO and UCHII regions investigated by the RMS survey. We review the methods used to determine distances, and investigate the radial galactocentric distribution of these sources in context with the observed structure of the galaxy. The distribution of MYSO and UCHII regions is found to be spatially correlated with the spiral arms and galactic bar. We examine the radial distribution of MYSOs and UCHII regions and find variations in the star formation rate between the inner and outer Galaxy and discuss the implications for star formation throughout the galactic disc.

  1. SEPARATING THE CONJOINED RED CLUMP IN THE GALACTIC BULGE: KINEMATICS AND ABUNDANCES

    SciTech Connect

    De Propris, Roberto; Kunder, Andrea; Rich, R. Michael; Johnson, Christian I.; Koch, Andreas; Brough, Sarah; Conselice, Christopher J.; Gunawardhana, Madusha; Wijesinghe, Dinuka; Palamara, David; Pimbblet, Kevin

    2011-05-10

    We have used the AAOMEGA spectrograph to obtain R {approx} 1500 spectra of 714 stars that are members of two red clumps in the Plaut Window Galactic bulge field (l, b) = (0{sup 0}, - 8{sup 0}). We discern no difference between the clump populations based on radial velocities or abundances measured from the Mgb index. The velocity dispersion has a strong trend with Mgb-index metallicity, in the sense of a declining velocity dispersion at higher metallicity. We also find a strong trend in mean radial velocity with abundance. Our red clump sample shows distinctly different kinematics for stars with [Fe/H] <-1, which may plausibly be attributable to a minority classical bulge or inner halo population. The transition between the two groups is smooth. The chemo-dynamical properties of our sample are reminiscent of those of the Milky Way globular cluster system. If correct, this argues for no bulge/halo dichotomy and a relatively rapid star formation history. Large surveys of the composition and kinematics of the bulge clump and red giant branch are needed to further define these trends.

  2. Space Observatory Studies of AGB Stars in Galaxies: from IRAS to JWST

    NASA Astrophysics Data System (ADS)

    Meixner, M.

    2011-09-01

    The precision measurements of space observatories, particularly infrared missions such as Spitzer, has spawned a renaissance in studies of AGB stars from the Milky Way, to nearby galaxies and beyond. This review summarizes the key areas in AGB star studies impacted by the space observatories of the past two decades, IRAS, ISO, Spitzer, and Akari and speculates on the future promise of the SOFIA, WISE and JWST missions. Drawing from results of IRAS, ISO and Spitzer studies, this review touches on topics such as AGB star identification in stellar populations, AGB mass-loss rate measurements, dust composition, and variability that set the stage for the future work. The past, present and future space missions can be used in combination to tackle some big questions which confront studies of both AGB stars and galaxies. What is the mass-loss return or dust and metal enrichment of galaxies by the AGB stars? How does this mass-loss return depend on the star formation history (i.e. age), metallicity and galactic environment? What is the time evolution of AGB stars and how does mass loss affect it? Improved models of stellar populations that properly include AGB stars will help our understanding of both AGB stars and galaxy evolution. What model results can we prepare now to capitalize on the present and future space observatory missions? How can we improve the period-luminosity relation of AGB stars not only to better understand AGB star physics but also to use as a distance indicator for galaxies?

  3. THE SPLIT RED CLUMP OF THE GALACTIC BULGE FROM OGLE-III

    SciTech Connect

    Nataf, D. M.; Gould, A.; Stanek, K. Z.; Udalski, A.; Fouque, P. E-mail: gould@astronomy.ohio-state.ed

    2010-09-20

    The red clump (RC) is found to be split into two components along several sightlines toward the Galactic bulge. This split is detected with high significance toward the areas (-3.5 < l < 1, b < -5) and (l, b) = (0, + 5.2), i.e., along the bulge minor axis and at least 5 deg off the plane. The fainter (hereafter 'main') component is the one that more closely follows the distance-longitude relation of the bulge RC. The main component is {approx}0.5 mag fainter than the secondary component and with an overall approximately equal population. For sightlines further from the plane, the difference in brightness increases, and more stars are found in the secondary component than in the main component. The two components have very nearly equal (V - I) color.

  4. 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.

  5. Wet disc contraction to galactic blue nuggets and quenching to red nuggets

    NASA Astrophysics Data System (ADS)

    Dekel, A.; Burkert, A.

    2014-02-01

    We study the origin of high-redshift, compact, quenched spheroids (red nuggets) through the dissipative shrinkage of gaseous discs into compact star-forming systems (blue nuggets). The discs, fed by cold streams, undergo violent disc instability that drives gas into the centre (along with mergers). The inflow is dissipative when its time-scale is shorter than the star formation time-scale. This implies a threshold of ˜0.28 in the cold-to-total mass ratio within the disc radius. For the typical gas fraction ˜0.5 at z ˜ 2, this threshold is traced back to a maximum spin parameter of ˜0.05, implying that ˜half the star-forming galaxies contract to blue nuggets, while the rest form extended stellar discs. Thus, the surface density of blue galaxies is expected to be bimodal about ˜109 M⊙ kpc-2, slightly increasing with mass. The blue nuggets are expected to be rare at low z when the gas fraction is low. The blue nuggets quench to red nuggets by complementary internal and external mechanisms. Internal quenching by a compact bulge, in a fast mode and especially at high z, may involve starbursts, stellar and active galactic nucleus feedback, or Q-quenching. Quenching due to hot-medium haloes above 1012 M⊙ provides maintenance and a slower mode at low redshift. These predictions are confirmed in simulations and are consistent with observations at z = 0-3.

  6. Studying the evolution of AGB stars in the Gaia epoch

    NASA Astrophysics Data System (ADS)

    Di Criscienzo, M.; Ventura, P.; García-Hernández, D. A.; Dell'Agli, F.; Castellani, M.; Marrese, P. M.; Marinoni, S.; Giuffrida, G.; Zamora, O.

    2016-10-01

    We present asymptotic giant branch (AGB) models of solar metallicity, to allow the interpretation of observations of Galactic AGB stars, whose distances should be soon available after the first release of the Gaia catalogue. We find an abrupt change in the AGB physical and chemical properties, occurring at the threshold mass to ignite hot bottom burning, i.e. 3.5 M⊙. Stars with mass below 3.5 M⊙ reach the C-star stage and eject into the interstellar medium gas enriched in carbon, nitrogen and 17O. The higher mass counterparts evolve at large luminosities, between 3 × 104 and 105 L⊙. The mass expelled from the massive AGB stars shows the imprinting of proton-capture nucleosynthesis, with considerable production of nitrogen and sodium and destruction of 12C and 18O. The comparison with the most recent results from other research groups is discussed, to evaluate the robustness of the present findings. Finally, we compare the models with recent observations of galactic AGB stars, outlining the possibility offered by Gaia to shed new light on the evolution properties of this class of objects.

  7. Can Star-Disk Collisions Explain the Missing Red Giants Problem in the Galactic Center?

    NASA Astrophysics Data System (ADS)

    Kieffer, T. Forrest; Bogdanović, Tamara

    2016-06-01

    Observations have revealed a relative paucity of red giant (RG) stars within the central 0.5 pc in the Galactic Center (GC). Motivated by this finding we investigate the hypothesis that collisions of stars with a fragmenting accretion disk are responsible for the observed dearth of evolved stars. We use three-dimensional hydrodynamic simulations to model a star with radius 10 R ⊙ and mass 1 M ⊙, representative of the missing population of RGs, colliding with high density clumps. We find that multiple collisions with clumps of column density ≳108 g cm-2 can strip a substantial fraction of the star’s envelope and in principle render it invisible to observations. Simulations confirm that repeated impacts are particularly efficient in driving mass loss as partially stripped RGs expand and have increased cross sections for subsequent collisions. Because the envelope is unbound on account of the kinetic energy of the star, any significant amount of stripping of the RG population in the GC should be mirrored by a systematic decay of their orbits and possibly by their enhanced rotational velocity. To be viable, this scenario requires that the total mass of the fragmenting disk has been several orders of magnitude higher than that of the early-type stars which now form the stellar disk in the GC.

  8. Li-rich red giant branch stars in the Galactic bulge

    NASA Astrophysics Data System (ADS)

    Gonzalez, O. A.; Zoccali, M.; Monaco, L.; Hill, V.; Cassisi, S.; Minniti, D.; Renzini, A.; Barbuy, B.; Ortolani, S.; Gomez, A.

    2009-12-01

    Aims. We present lithium abundance determination for a sample of K giant stars in the Galactic bulge. The stars presented here are the only 13 stars with a detectable lithium line (6767.18 Å) among 400 stars for which we have spectra in this wavelength range, half of them in Baade's Window (b=-4^circ) and half in a field at b=-6^circ. Methods: The stars were observed with the GIRAFFE spectrograph of FLAMES mounted on VLT, with a spectral resolution of R˜20 000. Abundances were derived from spectral synthesis and the results are compared with those of stars with similar parameters, but no detectable Li line. Results: We find 13 stars with a detectable Li line, among which 2 have abundances A(Li)>2.7. No clear correlations were found between the Li abundance and those of other elements. With the exception of the two most Li rich stars, the others follow a fairly tight A(Li)-T_eff correlation. Conclusions: There is strong indication of a Li production phase during the red giant branch (RGB), acting either on a very short timescale, or selectively only in some stars. That the proposed Li production phase is associated with the RGB bump cannot be excluded, although our targets are significantly brighter than the predicted RGB bump magnitude for a population at 8 kpc.

  9. Building the Galactic halo from globular clusters: evidence from chemically unusual red giants

    NASA Astrophysics Data System (ADS)

    Martell, S. L.; Smolinski, J. P.; Beers, T. C.; Grebel, E. K.

    2011-10-01

    We present a spectroscopic search for halo field stars that originally formed in globular clusters. Using moderate-resolution SDSS-III/SEGUE-2 spectra of 561 red giants with typical halo metallicities (-1.8 ≤ [Fe/H] ≤ -1.0), we identify 16 stars, 3% of the sample, with CN and CH bandstrength behavior indicating depleted carbon and enhanced nitrogen abundances relative to the rest of the data set. Since globular clusters are the only environment known in which stars form with this pattern of atypical light-element abundances, we claim that these stars are second-generation globular cluster stars that have been lost to the halo field via normal cluster mass-loss processes. Extrapolating from theoretical models of two-generation globular cluster formation, this result suggests that globular clusters contributed significant numbers of stars to the construction of the Galactic halo: we calculate that a minimum of 17% of the present-day mass of the stellar halo was originally formed in globular clusters. The ratio of CN-strong to CN-normal stars drops with Galactocentric distance, suggesting that the inner-halo population may be the primary repository of these stars. Full Tables 1 and 3 are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/534/A136

  10. 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.

  11. s-Process Abundances in AGB Stars At Various Metallicities and Their Theoretical Interpretation

    NASA Astrophysics Data System (ADS)

    Busso, M.; Gallino, R.

    1997-02-01

    Results from existing models of s-processing in red giants are compared with key observed abundances in population I and II AGB stars. Population I giants are particularly important for getting constraints on the neutron density (from Rb/Sr ratios), while population II AGB's provide clues to understand how the neutron exposure is achieved (through the ratio between Ba-peak and Sr-peak elements). AGB stars are shown to require s-processing with a very low neutron density, and producing very high Ba/Sr ratios at low metallicities. Both features are typical of radiative 13C-burning phases in AGB stars.

  12. REVEALING PROBABLE UNIVERSAL FEATURES IN THE LOWER RED GIANT BRANCH LUMINOSITY FUNCTIONS OF GALACTIC GLOBULAR CLUSTERS

    SciTech Connect

    Kravtsov, V. V.

    2009-06-15

    This paper aims at demonstrating, for the first time, very probable universal peculiarities of the evolution of stars in the lower red giant branch (RGB) of Galactic globular clusters (GCs), reflected in two corresponding dips in the luminosity functions (LFs). By relying on the database of Hubble Space Telescope photometry of GCs, we analyze the lower RGB LFs of a sample of 18 GCs in a wide metallicity range, {delta}[Fe/H] {approx} 1.9 dex. We first show that in the F555W-(F439W-F555W) color-magnitude diagrams (CMDs), the lower RGB of GCs, except for the most metal-poor of them, frequently shows an apparent 'knee'. It reveals itself as a fairly abrupt change of the RGB slope. At the same luminosity level, the RGB LFs show a feature in the form of a more or less pronounced dip. We find that the magnitude difference between the RGB base and the given feature is, on average, around {delta} F555W{sup dip} {sub base}{approx} 1.4 mag. It shows a marginal variation with metallicity, if any, comparable to the error. At the same time, the magnitude difference between the dip and the RGB bump, {delta} F555W{sup bump} {sub dip}, decreases with increasing metallicity and falls within the range 0.8 {approx}< {delta} F555W{sup bump} {sub dip} {approx}< 1.7 mag. Generalized LFs (GLFs) have been obtained for three subsamples of GCs within limited metallicity ranges and with different horizontal branch (HB) morphology. They reproduce the 'knee-related' dip that is statistically significant in two of the GLFs. This feature turns out to be more pronounced in the GLFs of GCs with either the blue or red HB morphology than with the intermediate one. The same GLFs also reveal an additional probable universal dip. It shows up below the RGB bump at {delta} F555W slightly increasing from {approx}0.3 to {approx}0.5 mag with increasing metallicity. Also, the statistical significance of this 'prebump' dip increases, on average, toward higher metallicity. Except for the well known RGB bump, no

  13. 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.

  14. Dust input from AGB stars in the Large Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Zhukovska, S.; Henning, T.

    2013-07-01

    Aims: The dust-forming population of AGB stars and their input to the interstellar dust budget of the Large Magellanic Cloud (LMC) are studied with evolutionary dust models with the main goals (1) to investigate how the amount and composition of dust from AGB stars vary over the galactic history; (2) to characterise the mass and metallicity distribution of the present population of AGB stars; (3) to quantify the contribution of AGB stars of different mass and metallicity to the present stardust population in the interstellar medium (ISM). Methods: We used models of the stardust lifecycle in the ISM developed and tested for the solar neighbourhood. The first global spatially resolved reconstruction of the star formation history of the LMC from the Magellanic Clouds Photometric Survey was employed to calculate the stellar populations in the LMC. Results: The dust input from AGB stars is dominated by carbon grains from stars with masses ≲4 M⊙ almost during the entire history of the LMC. The production of silicate, silicon carbide, and iron dust is delayed until the ISM is enriched to about half the present metallicity in the LMC. For the first time, theoretically calculated dust production rates of AGB stars are compared with those derived from infrared observations of AGB stars for the entire galaxy. We find good agreement within scatter of various observational estimates. We show that the majority of silicate and iron grains in the present stardust population originate from a small population of intermediate-mass stars consisting of only ≲4% of the total number of stars, whereas in the solar neighbourhood they originate from low-mass stars. With models of the lifecycle of stardust grains in the ISM we confirm the strong discrepancy between dust input from stars and the existing interstellar dust mass in the LMC reported previously.

  15. A preliminary systematic search for red-clump stars in Galactic open clusters based on 2mass data

    NASA Astrophysics Data System (ADS)

    Zhang, Xi; Chen, Li; Li, Zhongmu

    2013-02-01

    Red-clump (RC) giants are intermediate-age, core-helium-burning stars. The RC can be used as a standard candle. In particular, the small variance of the RC's K-band intrinsic luminosity and its weak dependence on chemical composition and age make it an extremely useful distance indicator. In this paper, we use 2mass data to search for RC stars in a sample of 60 Galactic open clusters with known reddening, ages, and distances, and obtain an average value for the RC's absolute K s-band magnitude, M K s = -1.72 +/- 0.17 mag.

  16. 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.

  17. Infrared spectroscopy of AGB/post-AGB stars

    NASA Astrophysics Data System (ADS)

    Venkataraman, V.; Anandarao, B. G.

    During their asymptotic giant branch (AGB) stage, intermediate mass stars undergo substantial mass loss believed to be triggered by pulsational shocks and radiation pressure. Near-infrared spectroscopy is one of the recognised tools to study the mass loss esses. We have carried out H and K band spectroscopy at Mt Abu observatory using the NICMOS camera/spectrograph at a spectral resolution of ~ 1000 on a sample of more than 70 AGB/Post-AGB stars of different types: M types, S types, SR types and some post-AGB stars or transition objects. We present here results on the equivalent widths of various spectral lines and discuss these in the light of the intrinsic properties of these stars like the pulsation period and near and far infrared colours. On a few selected post-AGB stars, we present SPITZER archival spectra in the region 6-30 micron. The spectral features detected in this region will be highlighted. We also present modelling of circumstellar matter in a number of these stars in order to determine the mass loss rate and dust optical depths. A clear difference is seen in these parameters in different types of AGB stars. Implications of these results will be discussed in terms of evolution of these stars.

  18. 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).

  19. RED GIANT BRANCH BUMP BRIGHTNESS AND NUMBER COUNTS IN 72 GALACTIC GLOBULAR CLUSTERS OBSERVED WITH THE HUBBLE SPACE TELESCOPE

    SciTech Connect

    Nataf, David M.; Gould, Andrew P.; Pinsonneault, Marc H.; Udalski, Andrzej

    2013-04-01

    We present the broadest and most precise empirical investigation of red giant branch bump (RGBB) brightness and number counts ever conducted. We implement a new method and use data from two Hubble Space Telescope globular cluster (GC) surveys to measure the brightness and star counts of the RGBB in 72 GCs. The median measurement precision is 0.018 mag in the brightness and 31% in the number counts, respectively, reaching peak precision values of 0.005 mag and 10%. The position of the main-sequence turnoff and the number of horizontal branch stars are used as comparisons where appropriate. Several independent scientific conclusions are newly possible with our parameterization of the RGBB. Both brightness and number counts are shown to have second parameters in addition to their strong dependence on metallicity. The RGBBs are found to be anomalous in the GCs NGC 2808, 5286, 6388, and 6441, likely due to the presence of multiple populations. Finally, we use our empirical calibration to predict the properties of the Galactic bulge RGBB. The updated RGBB properties for the bulge are shown to differ from the GC-calibrated prediction, with the former having lower number counts, a lower brightness dispersion, and a brighter peak luminosity than would be expected from the latter. This discrepancy is well explained by the Galactic bulge having a higher helium abundance than expected from GCs, {Delta}Y {approx} +0.06 at the median metallicity.

  20. The Chemical Composition of Red Giant Branch Stars in the Galactic Globular Clusters NGC 6342 and NGC 6366

    NASA Astrophysics Data System (ADS)

    Johnson, Christian I.; Caldwell, Nelson; Rich, R. Michael; Pilachowski, Catherine A.; Hsyu, Tiffany

    2016-07-01

    We present radial velocities and chemical abundances for red giant branch stars in the Galactic bulge globular clusters NGC 6342 and NGC 6366. The velocities and abundances are based on measurements of high-resolution (R ≳ 20,000) spectra obtained with the MMT-Hectochelle and WIYN-Hydra spectrographs. We find that NGC 6342 has a heliocentric radial velocity of +112.5 km s-1 (σ = 8.6 km s-1), NGC 6366 has a heliocentric radial velocity of -122.3 km s-1 (σ = 1.5 km s-1), and both clusters have nearly identical metallicities ([Fe/H] ≈ -0.55). NGC 6366 shows evidence of a moderately extended O-Na anti-correlation, but more data are needed for NGC 6342 to determine if this cluster also exhibits the typical O-Na relation likely found in all other Galactic globular clusters. The two clusters are distinguished from similar metallicity field stars as having larger [Na/Fe] spreads and enhanced [La/Fe] ratios, but we find that NGC 6342 and NGC 6366 display α and Fe-peak element abundance patterns that are typical of other metal-rich ([Fe/H] > -1) inner Galaxy clusters. However, the median [La/Fe] abundance may vary from cluster-to-cluster.

  1. Red Giant Branch Bump Brightness and Number Counts in 72 Galactic Globular Clusters Observed with the Hubble Space Telescope

    NASA Astrophysics Data System (ADS)

    Nataf, David M.; Gould, Andrew P.; Pinsonneault, Marc H.; Udalski, Andrzej

    2013-04-01

    We present the broadest and most precise empirical investigation of red giant branch bump (RGBB) brightness and number counts ever conducted. We implement a new method and use data from two Hubble Space Telescope globular cluster (GC) surveys to measure the brightness and star counts of the RGBB in 72 GCs. The median measurement precision is 0.018 mag in the brightness and 31% in the number counts, respectively, reaching peak precision values of 0.005 mag and 10%. The position of the main-sequence turnoff and the number of horizontal branch stars are used as comparisons where appropriate. Several independent scientific conclusions are newly possible with our parameterization of the RGBB. Both brightness and number counts are shown to have second parameters in addition to their strong dependence on metallicity. The RGBBs are found to be anomalous in the GCs NGC 2808, 5286, 6388, and 6441, likely due to the presence of multiple populations. Finally, we use our empirical calibration to predict the properties of the Galactic bulge RGBB. The updated RGBB properties for the bulge are shown to differ from the GC-calibrated prediction, with the former having lower number counts, a lower brightness dispersion, and a brighter peak luminosity than would be expected from the latter. This discrepancy is well explained by the Galactic bulge having a higher helium abundance than expected from GCs, ΔY ~ +0.06 at the median metallicity.

  2. 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.

  3. Post-AGB Stars in the Magellanic Clouds: Preliminary Results

    NASA Astrophysics Data System (ADS)

    Kamath, D.; Wood, P. R.; van Winckel, H.; van Aarle, E.

    2011-12-01

    The evolution and mass-loss of red giants is poorly understood. It is difficult to empirically estimate the mass-loss rate and the chemical abundance changes, as a function of initial mass and metallicity. Post-AGB stars are key objects in the study of the dramatic chemical and morphological changes of stars along the AGB ascent and subsequent evolution towards the Planetary Nebula phase. Thus studying these objects would help in understanding the different physical processes and the chemical evolution that occur during these evolutionary phases. Using the AAOmega multi-fibre spectrograph on the AAT, we carried out an extensive low-resolution spectral survey of several thousand post-AGB candidates, in the Large Magellanic Cloud and the Small Magellanic Cloud. The candidates were selected from the mid-IR Spitzer Space Telescope surveys: SAGE and SAGE-SMC. In this paper we present preliminary results from our survey, delineating the regions of the HR diagram where post-AGB stars are found and where Hα-emission occurs.

  4. Non-LTE sodium abundance in galactic thick- and thin-disk red giants

    NASA Astrophysics Data System (ADS)

    Alexeeva, S. A.; Pakhomov, Yu. V.; Mashonkina, L. I.

    2014-07-01

    The non-LTE sodium abundance has been determined from the Na I 6154 and 6161 Å lines for 38 thin-disk stars (15 of them are Ba II stars), 15 thick-disk stars, 13 Hercules-stream stars, and 13 stars that cannot be attributed neither to the thick Galactic disk nor to the thin one. The Na I model atom has been constructed using the most accurate present-day atomic data. For the Na I 6154 and 6161 Å lines, the non-LTEabundance corrections are from -0.06 to -0.24 dex, depending on the stellar parameters. No differences in [Na/Fe] abundance between the thick and thin disks have been detected; the derived ratios are close to the solar ones. The existence of a [Na/Fe] overabundance in the Ba II stars has been confirmed. The Hercules-stream stars exhibit nearly solar [Na/Fe] ratios. The results obtained can be used to test the sodium nucleosynthesis models.

  5. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2010-11-01

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

  7. FUNDAMENTAL PARAMETERS, INTEGRATED RED GIANT BRANCH MASS LOSS, AND DUST PRODUCTION IN THE GALACTIC GLOBULAR CLUSTER 47 TUCANAE

    SciTech Connect

    McDonald, I.; Zijlstra, A. A.; Boyer, M. L.; Gordon, K.; Meixner, M.; Sewilo, M.; Shiao, B.; Whitney, B.; Van Loon, J. Th.; Hora, J. L.; Robitaille, T.; Babler, B.; Meade, M.; Block, M.; Misselt, K.

    2011-04-01

    Fundamental parameters and time evolution of mass loss are investigated for post-main-sequence stars in the Galactic globular cluster 47 Tucanae (NGC 104). This is accomplished by fitting spectral energy distributions (SEDs) to existing optical and infrared photometry and spectroscopy, to produce a true Hertzsprung-Russell diagram. We confirm the cluster's distance as d = 4611{sup +213}{sub -200} pc and age as 12 {+-} 1 Gyr. Horizontal branch models appear to confirm that no more red giant branch mass loss occurs in 47 Tuc than in the more metal-poor {omega} Centauri, though difficulties arise due to inconsistencies between the models. Using our SEDs, we identify those stars that exhibit infrared excess, finding excess only among the brightest giants: dusty mass loss begins at a luminosity of {approx}1000 L{sub sun}, becoming ubiquitous above L = 2000 L{sub sun}. Recent claims of dust production around lower-luminosity giants cannot be reproduced, despite using the same archival Spitzer imagery.

  8. THE FRAGMENTING PAST OF THE DISK AT THE GALACTIC CENTER: THE CULPRIT FOR THE MISSING RED GIANTS

    SciTech Connect

    Amaro-Seoane, Pau; Chen, Xian E-mail: Xian.Chen@aei.mpg.de

    2014-01-20

    Since 1996 we have known that the Galactic Center (GC) displays a core-like distribution of red giant branch (RGB) stars starting at ∼10'', which poses a theoretical problem because the GC should have formed a segregated cusp of old stars. This issue has been addressed invoking stellar collisions, massive black hole binaries, and infalling star clusters, which can explain it to some extent. Another observational fact, key to the work presented here, is the presence of a stellar disk at the GC. We postulate that the reason for the missing stars in the RGB is closely intertwined with the disk formation process, which initially was gaseous and went through a fragmentation phase to form the stars. Using simple analytical estimates, we prove that during fragmentation the disk developed regions with densities much higher than a homogeneous gaseous disk, i.e., ''clumps'', which were optically thick, and hence contracted slowly. Stars in the GC interacted with them and in the case of RGB stars, the clumps were dense enough to totally remove their outer envelopes after a relatively low number of impacts. Giant stars in the horizontal branch (HB), however, have much denser envelopes. Hence, the fragmentation phase of the disk must have had a lower impact on their distribution, because it was more difficult to remove their envelopes. We predict that future deeper observations of the GC should reveal less depletion of HB stars and that the released dense cores of RGB stars will still be populating the GC.

  9. Wide Field Near-infrared Photometry of 12 Galactic Globular Clusters: Observations Versus Models on the Red Giant Branch

    NASA Astrophysics Data System (ADS)

    Cohen, Roger E.; Hempel, Maren; Mauro, Francesco; Geisler, Douglas; Alonso-Garcia, Javier; Kinemuchi, Karen

    2015-12-01

    We present wide field near-infrared (near-IR) photometry of 12 Galactic globular clusters, typically extending from the tip of the cluster red giant branch (RGB) to the main sequence turnoff. Using recent homogenous values of cluster distance, reddening and metallicity, the resulting photometry is directly compared to the predictions of several recent libraries of stellar evolutionary models. Of the sets of models investigated, Dartmouth and Victoria-Regina models best reproduce the observed RGB morphology, albeit with offsets in J-{K}S color which vary in their significance in light of all sources of observational uncertainty. Therefore, we also present newly recalibrated relations between near-IR photometric indices describing the upper RGB versus cluster iron abundance as well as global metallicity. The influence of enhancements in alpha elements and helium are analyzed, and we find that the former affect the morphology of the upper RGB in accord with model predictions. Meanwhile, the empirical relations we derive are in good agreement with previous results, and minor discrepancies can likely be attributed to differences in the assumed cluster distances and reddenings. In addition, we present measurements of the horizontal branch (HB) and RGB bump magnitudes, finding a non-negligible dependence of the near-IR HB magnitude on cluster metallicity. Lastly, we discuss the influence of assumed cluster distances, reddenings and metallicities on our results, finding that our empirical relations are generally insensitive to these factors to within their uncertainties.

  10. 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.

  11. Low-Resolution Spectrum of the Diffuse Galactic Light and 3.3 μm PAH Emission with the AKARI InfraRed Camera

    NASA Astrophysics Data System (ADS)

    Tsumura, Kohji; Matsumoto, Toshio; Matsuura, Shuji; Sakon, Itsuki; Tanaka, Masahiro; Wada, Takehiko

    2013-12-01

    We first obtained the spectrum of the diffuse Galactic light (DGL) at general interstellar space in the 1.8-5.3μm wavelength region with the low-resolution prism spectroscopy mode of the AKARI Infra-Red Camera (IRC) NIR channel. The 3.3μm m PAH band is detected in the DGL spectrum at Galactic latitude |b| < 15˚, and its correlations with the Galactic dust and gas are confirmed. The correlation between the 3.3μm PAH band and the thermal emission from the Galactic dust is expressed not by a simple linear correlation, but by a relation with extinction. Using this correlation, the spectral shape of DGL at an optically thin region (5˚ < |b| < 15˚) was derived as a template spectrum. Assuming that the spectral shape of this template spectrum is uniform at any position, the DGL spectrum can be estimated by scaling this template spectrum using the correlation between the 3.3μm PAH band and the thermal emission from the Galactic dust.

  12. The optically bright post-AGB population of the LMC

    NASA Astrophysics Data System (ADS)

    van Aarle, Els; van Winckel, Hans; Evans, Tom Lloyd; Wood, Peter R.

    2009-03-01

    The detected variety in chemistry and circumstellar shell morphology of the limited sample of Galactic post-AGB stars is so large, that there is no consensus yet on how individual objects are linked by evolutionary channels. The evaluation is complicated by the fact that the distances and hence luminosities of these objects are poorly known. In this contribution we report on our project to overcome this problem by focusing on a significant sample of post-AGB stars with known distances: those in the LMC. Via cross-correlation of the infrared SAGE-SPITZER catalogue with optical catalogues we selected a sample of 322 LMC post-AGB candidates based on their position in the various colour-colour diagrams. We determined the fundamental properties of 82 of them, using low resolution optical spectra that we obtained at Siding Spring and SAAO. We selected a subsample to be studied at high spectral resolution in order to obtain accurate abundances of a wide range of species. This will allow us to connect the theoretical predictions with the obtained surface chemistry at a given luminosity and metallicity. By this, we want to constrain important structure parameters of the evolutionary models. Preliminary results of the selection process are presented.

  13. A Direct Measurement of Lifetimes and Stellar Luminosities on the AGB

    NASA Astrophysics Data System (ADS)

    Kalirai, Jason S.; Marigo, Paola; Tremblay, Pier-Emmanuel

    2015-01-01

    The asymptotic giant branch (AGB) represents the phase of stellar evolution where stars become their brightest and reddest. As such, understanding stellar lifetimes and luminosities during this evolutionary phase is crucial to accurately interpret red and infrared light from galaxies using population synthesis models. Recently, there has been much controversy over the inferred ages and masses of infrared galaxies due to our lack of understanding of this phase. In this presentation, I'll present a direct measurement of the stellar core mass growth on the AGB by comparing the initial core masses to the post AGB core masses measured from spectroscopy of white dwarfs. The resulting data allows us to calculate the stellar lifetime and luminosity on the AGB, and to compare to popular models that are used to interpret light from distant galaxies.

  14. OPTICAL/NEAR-INFRARED SELECTION OF RED QUASI-STELLAR OBJECTS: EVIDENCE FOR STEEP EXTINCTION CURVES TOWARD GALACTIC CENTERS?

    SciTech Connect

    Fynbo, J. P. U.; Krogager, J.-K.; Vestergaard, M.; Geier, S.; Venemans, B.; Noterdaeme, P.; Moller, P.; Ledoux, C.

    2013-01-15

    We present the results of a search for red QSOs using a selection based on optical imaging from the Sloan Digital Sky Survey (SDSS) and near-infrared imaging from UKIDSS. Our main goal with the selection is to search for QSOs reddened by foreground dusty absorber galaxies. For a sample of 58 candidates (including 20 objects fulfilling our selection criteria that already have spectra in the SDSS), 46 (79%) are confirmed to be QSOs. The QSOs are predominantly dust-reddened except for a handful at redshifts z {approx}> 3.5. However, the dust is most likely located in the QSO host galaxies (and for two, the reddening is primarily caused by Galactic dust) rather than in the intervening absorbers. More than half of the QSOs show evidence of associated absorption (BAL absorption). Four (7%) of the candidates turned out to be late-type stars, and another four (7%) are compact galaxies. We could not identify the remaining four objects. In terms of their optical spectra, these QSOs are similar to the QSOs selected in the FIRST-2MASS Red Quasar Survey except they are on average fainter, more distant, and only two are detected in the FIRST survey. As per the usual procedure, we estimate the amount of extinction using the SDSS QSO template reddened by Small-Magellanic-Cloud-(SMC) like dust. It is possible to get a good match to the observed (rest-frame ultraviolet) spectra, but it is not possible to match the observed near-IR photometry from UKIDSS for nearly all the reddened QSOs. The most likely reasons are that the SDSS QSO template is too red at optical wavelengths due to contaminating host galaxy light and because the assumed SMC extinction curve is too shallow. Three of the compact galaxies display old stellar populations with ages of several Gyr and masses of about 10{sup 10} M{sub Sun} (based on spectral energy distribution modeling). The inferred stellar densities in these galaxies exceed 10{sup 10} M{sub Sun} kpc{sup -2}, which is among the highest measured for early

  15. Charged polycyclic aromatic hydrocarbon clusters and the galactic extended red emission

    PubMed Central

    Rhee, Young Min; Lee, Timothy J.; Gudipati, Murthy S.; Allamandola, Louis J.; Head-Gordon, Martin

    2007-01-01

    The species responsible for the broad extended red emission (ERE), discovered in 1975 and now known to be widespread throughout the Galaxy, still is unidentified. Spanning the range from ≈540 to 900 nm, the ERE is a photoluminescent process associated with a wide variety of different interstellar environments. Over the years, a number of plausible candidates have been suggested, but subsequent observations ruled them out. The objects that present the ERE also emit the infrared features attributed to free polycyclic aromatic hydrocarbon (PAH) molecules, suggesting that closely related materials are plausible ERE carriers. Here, we show that the peculiar spectra and unique properties of closed-shell cationic PAH dimers satisfy the existing observational constraints and suggest that emission from mixtures of charged PAH clusters accounts for much of the ERE. This work provides a view into the structures, stabilities, abundances, and ionization balance of PAH-related species in the emission zones, which, in turn, reflects physical conditions in the emission zones and sheds fundamental light on the nanoscale processes involved in carbon-particle nucleation and growth and carbonaceous dust evolution in the interstellar medium. PMID:17372209

  16. Hot Post-AGB Stars

    NASA Astrophysics Data System (ADS)

    Parthasarathy, M.; Gauba, G.; Fujii, T.; Nakada, Y.

    2001-08-01

    From the study of IRAS sources with far-IR colors similar to planetary nebulae (PNe), several proto-planetary nebulae with hot (OB) post-AGB central stars have been detected. These stars form an evolutionary link between the cooler G,F,A supergiant stars that have evolved off the Asymptotic Giant Branch (AGB) and the hot (OB) central stars of PNe. The optical spectra of these objects show strong Balmer emission lines and in some cases low excitation nebular emission lines such as [NII] and [SII] superposed on the OB stellar continuum. The absence of of [OIII] 5007Å line and the presence of low excitation nebular emission lines indicate that photoionisation has just started. The UV(IUE) spectra of some of these objects revealed violet shifted stellar wind P-Cygni profiles of CIV, SiIV and NV, indicating hot and fast stellar wind and post-AGB mass loss. These objects appear to be rapildy evolving into the early stages of PNe similar to that observed in the case of Hen1357 IRAS 17119-5926 (Stingray Nebula) and IRAS 18062+2410 SAO85766.

  17. 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.

  18. INFRARED TWO-COLOR DIAGRAMS FOR AGB STARS, POST-AGB STARS, AND PLANETARY NEBULAE

    SciTech Connect

    Suh, Kyung-Won

    2015-08-01

    We present various infrared two-color diagrams (2CDs) for asymptotic giant branch (AGB) stars, post-AGB stars, and Planetary Nebulae (PNe) and investigate possible evolutionary tracks. We use catalogs from the available literature for the sample of 4903 AGB stars (3373 O-rich; 1168 C-rich; 362 S-type), 660 post-AGB stars (326 post-AGB; 334 pre-PN), and 1510 PNe in our Galaxy. For each object in the catalog, we cross-identify the IRAS, AKARI, Midcourse Space Experiment, and 2MASS counterparts. The IR 2CDs can provide useful information about the structure and evolution of the dust envelopes as well as the central stars. To find possible evolutionary tracks from AGB stars to PNe on the 2CDs, we investigate spectral evolution of post-AGB stars by making simple but reasonable assumptions on the evolution of the central star and dust shell. We perform radiative transfer model calculations for the detached dust shells around evolving central stars in the post-AGB phase. We find that the theoretical dust shell model tracks using dust opacity functions of amorphous silicate and amorphous carbon roughly coincide with the densely populated observed points of AGB stars, post-AGB stars, and PNe on various IR 2CDs. Even though some discrepancies are inevitable, the end points of the theoretical post-AGB model tracks generally converge in the region of the observed points of PNe on most 2CDs.

  19. 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.

  20. Duration of the Early Galactic Formation Epoch: HST Photometry for Red-Horizontal Branch Clusters in the Outer Halo

    NASA Astrophysics Data System (ADS)

    Hesser, J. E.; Stetson, P. B.; McClure, R. D.; van den Bergh, S.; Bolte, M.; Harris, W. E.; van den Berg, D. A.; Bell, R. A.; Fahlman, G. G.; Richer, H. B.; Bond, H. E.

    1997-12-01

    Last year we presented evidence from HST photometry of the low-metallicity cluster NGC 2419 (M_V = -9.5, R_⊙ ~ 90 kpc, [Fe/H] = -2.2) that globular cluster formation began at essentially the same time throughout a region of the Galactic halo now almost 200 kpc in diameter (Harris et al. 1997 AJ 114, 1030). We now turn to the time spread of halo formation, with the ultimate aim of addressing the relative roles of mergers over the first 4 or more Gyrs (Searle & Zinn 1978, ApJ, 225, 357; Lee, Demarque & Zinn 1994 ApJ, 423, 248) versus models favoring a rapid collapse (Eggen, Lynden-Bell & Sandage 1962, ApJ, 236, 748; Stetson, VandenBerg & Bolte 1996, PASP, 108, 560), or some combination of those and other processes. We provide the first reliable measurements from the giant branch through the main-sequence turnoffs of red-horizontal-branch clusters in the outer halo, which are frequently postulated to be younger than most other globular clusters. From WFPC2 F555W (`V') and F814W (`I') photometry for Pal 3 (M_V = -5.2, R_⊙ ~ 87 kpc), Pal 4 (M_V = -5.8, R_⊙ ~ 98 kpc), and Eridanus (M_V = -4.8, R_⊙ ~ 78 kpc), all with [Fe/H] ~ -1.5, we estimate their relative ages by making differential comparisons among them and with respect to inner-halo objects of, presumably, comparable chemical compositions. It seems likely at this stage of our analysis that (a) the three clusters are the same age to our measurement precision of ~ 1 Gyr, and, (b) the CMDs of all three outer halo clusters differ from those of M 3 and M 5 (our template clusters of similar metallicity), in the sense that the outer halo clusters are younger by ~ 3 Gyr, or they are ~ 0.5 dex more metal-rich than currently thought. Large uncertainties in chemical compositions (He, [alpha /Fe], [CNO/Fe]) for outer halo and template clusters alike mask the true interpretation.

  1. AGB Stars In AKARI And IRAS Two-color Diagrams

    NASA Astrophysics Data System (ADS)

    Koopman, Kristen; Sjouwerman, L.; Claussen, M.

    2011-01-01

    Infrared measurements such as from the Infrared Astronomical Satellite (IRAS) all-sky survey and the Midcourse Space Experiment (MSX) Galactic plane survey have been used to statistically distinguish between different types of objects. In particular, two-color diagrams characterize Asymptotic Giant Branch (AGB) stars with different circumstellar shell opacity and thickness, and whether the source is oxygen- or carbon-rich in nature (Van der Veen & Habing 1988, A&A 194, 125; Sjouwerman et al. 2009, ApJ 795, 1554). We present two-color diagrams for AGB stars using infrared data from the AKARI satellite all-sky survey (e.g. Ishihara et al. 2010, A&A 514, A1) and created categories analogous to those for IRAS and MSX two-color diagrams. Our system specifically selects for circumstellar envelopes that are conducive in sustaining SiO maser emission. About 200 new sources were identified in the AKARI data. This research was supported by the Research Experience for Undergraduate Program of the National Science Foundation, and was completed at the National Radio Astronomy Observatory in Socorro, New Mexico.

  2. 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%.

  3. 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.

  4. Spectral classification of photometrically selected AGB candidates in NGC 6822

    NASA Astrophysics Data System (ADS)

    Sibbons, L. F.; Ryan, S. G.; Napiwotzki, R.; Thompson, G. P.

    2015-02-01

    Context. The ratio of C- and M-type asymptotic giant branch (AGB) stars is commonly used to estimate the metallicity of extragalactic populations. Sources in the AGB population must therefore be accurately classified as either C- or M-type. Spectroscopic data are presented for candidate C- and M-type AGB stars, previously classified using JHK photometry, in the Local Group dwarf galaxy NGC 6822. Aims: This paper aims to evaluate the success of the JHK classification criteria used in order to determine the level of error associated with this method, and to refine the criteria for future studies. The success rate of a second independent method of source classification, the CN-TiO method, is also examined. We also review the validity of the 4 kpc radial limit imposed in our previous work. Methods: Spectra of 323 sources, distributed across an area of 2 deg2, were taken using the AAOmega multi-fibre spectrograph on the Anglo-Australian Telescope and have been classified using an automated classification system and spectral standards from the literature. Nearly half (135) of these sources were selected in common with a photometric catalogue that relied on the CN-TiO method. Results: Within this sample we were able to classify 158 sources, including 82 C-type giants and one anomalous M-type giant, all members of NGC 6822, and 75 foreground K- and M-type dwarf sources. All but three of the giant sources are located within 3 kpc of the galactic centre. Using this spectroscopic sample, new JHK photometric criteria for the isolation and classification of C- and M-type AGB stars have been derived. The error rate in the CN-TiO method, arising from stars incorrectly classified as C-type, has been estimated to be ~7%. Conclusions: Based on the new JHK classification criteria, revised estimates of the global C/M ratio, 0.95 ± 0.04, and iron abundance, -1.38 ± 0.06 dex, are presented for NGC 6822. Tables 1, and 10-13 are available in electronic form at http://www.aanda.org

  5. Production of 26Al by super-AGB stars

    NASA Astrophysics Data System (ADS)

    Siess, L.; Arnould, M.

    2008-10-01

    Context: Super AGB (SAGB) stars have initial masses ranging between 7-11 {M_⊙} and develop efficient hydrogen burning at the base of their convective envelope during their AGB evolution, leading to a substantial production of {}26Alg. Aims: We present the first discussion of the contribution of the SAGB stars to the galactic {}26Alg production, and we estimate the main uncertainties that affect the determination of the {}26Alg yields. Methods: The results of full stellar evolution computations are presented, with special emphasis on the {}26Alg yields from SAGB stars. We also use a postprocessing nucleosynthesis code to quantify the uncertainties associated with the nuclear reaction rates and with the treatment of convection that modifies the thermodynamical conditions at the base of the convective envelope. Results: Hot bottom burning leads to individual SAGB {}26Alg yields that are larger than those from intermediate mass stars, amounting to typical values as high as 5 × 10-5 {M_⊙}. The overall SAGB contribution remains modest, however, not exceeding 0.3 {M_⊙} of the estimated galactic content of 2.8 {M_⊙}. On the other hand, the SAGB 26Al/27Al ratios always exceed 0.01, which is commensurable with the values measured in some SiC grains considered to originate in C-rich AGB stars. However, the isotopic composition of some other elements, particularly nitrogen, is clearly at variance with the observations. We find that the {}26Alg yields are not affected by the pollution induced by the third dredge-ups, but that they strongly depend on the evolution of the temperature at the base of the convective envelope, the determination of which remains highly dependent on the specific convection model used in the stellar computations. Modifications of T_env by ± 10% leads to variations in the {}26Alg yields by a factor of 0.2 to 6. In comparison, the nuclear reaction rate uncertainties have less of an impact, altering the yields by less than a factor of 2.

  6. 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

  7. 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.

  8. FRUITY Upgrades on AGB Evolution and Nucleosynthesis

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

    Asymptotic Giant Branch (AGB) stars are among the major polluters of the interstellar medium. These objects produce both light (C, N, O, F, Na) and heavy elements (via the slow neutron capture process, the s-process). We have devoted a long-standing project to study the physical and chemical properties of AGB stars. Our models are available on the on-line FRUITY database, which currently provides the surface isotopic compositions and yields from hydrogen to lead of low-mass AGB stars (1.3 ≤ M/M⊙ ≤ 3.0). We present a new set of intermediate-mass AGB models (4.0, 5.0 and 6.0 M⊙ with -2.15 ≤ [Fe/H] ≤ +0.15). We discuss their physical and chemical properties, highlighting the differences with respect to the set already on-line. Moreover, we check the reliability of our models by comparing them to observed quantities, such as the initial-to-final mass relation and AGB luminosity functions.

  9. 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.

  10. Variability And Mass-loss From Agb Stars In The Lmc

    NASA Astrophysics Data System (ADS)

    Riebel, David; Meixner, M.; Srinivasan, S.; Fraser, O.; Babler, B.; Block, M.; Bracker, S.; Engelbracht, S.; Gordon, K.; Hora, J.; Indebetouw, R.; Leitherer, C.; Meade, M.; Misselt, K.; Whitney, B.; Sewilo, M.; Vijh, U.

    2009-01-01

    Mass loss from evolved stars on the Asymptotic Giant Branch (AGB) is an important factor in both stellar and galactic evolution; the total amount of mass lost determines the star's eventual fate as a compact object and plays a significant role in the chemical enrichment of the interstellar medium. We combine excess infrared emission derived by Srinivasan et al. (2008) from the Spitzer SAGE survey of the LMC (Meixner, et al. 2006) with variability parameters derived from the MACHO survey (Fraser, et al. 2008, in press) to examine the effects of stellar variability on mass loss from evolved stars on the AGB. We find that stellar populations differing in chemical composition show different relationships between mass loss and the period and amplitude of variation, while general trends of increasing mass loss with increasing variability are visible in all populations.

  11. 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.

  12. The Outflows of Binary AGB Stars

    NASA Astrophysics Data System (ADS)

    Ramstedt, S.; Vlemmings, W. H. T.; Mohamed, S.

    2015-12-01

    The required conditions for stars to evolve into planetary nebulae (PNs) continues to puzzle. Since PNs are found in a wide variety of shapes, processes that could sculpt circumstellar envelopes (CSEs) are being investigated. A binary companion will have a strong gravitational effect, but known binary AGB stars are rare. Using ALMA in Cycle 1 and 2, we have observed a small sample of well-studied, binary AGB stars, covering a decisive range in separation, in order to determine the influence of a companion on the circumstellar morphology of the AGB primary. The first steps toward interpreting and analyzing the data have been taken, and the results will be compared to 3D Smoothed Particle Hydrodynamics (SPH) models of the gravitational interaction.

  13. 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.

  14. Chemical Abundances in Field Red Giants from High-resolution H-band Spectra Using the APOGEE Spectral Linelist

    NASA Astrophysics Data System (ADS)

    Smith, Verne V.; Cunha, Katia; Shetrone, Matthew D.; Meszaros, Szabolcs; Allende Prieto, Carlos; Bizyaev, Dmitry; Garcìa Pèrez, 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 (α Boo and μ Leo), two M-giants (β And and δ 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 12C, 13C, 14N, and 16O, 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 12C synthesized during 4He-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 ~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.

  15. 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.

  16. 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…

  17. 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…

  18. 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…

  19. 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:…

  20. 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…

  1. The Facilities Committee. AGB Effective Committee Series

    ERIC Educational Resources Information Center

    Kaiser, Harvey H.

    2012-01-01

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

  2. STAR-TO-STAR IRON ABUNDANCE VARIATIONS IN RED GIANT BRANCH STARS IN THE GALACTIC GLOBULAR CLUSTER NGC 3201

    SciTech Connect

    Simmerer, Jennifer; Ivans, Inese I.; Filler, Dan; Francois, Patrick; Charbonnel, Corinne; Monier, Richard; James, Gaeel E-mail: iii@physics.utah.edu E-mail: patrick.francois@obspm.fr E-mail: richard.monier@unice.fr

    2013-02-10

    We present the metallicity as traced by the abundance of iron in the retrograde globular cluster NGC 3201, measured from high-resolution, high signal-to-noise spectra of 24 red giant branch stars. A spectroscopic analysis reveals a spread in [Fe/H] in the cluster stars at least as large as 0.4 dex. Star-to-star metallicity variations are supported both through photometry and through a detailed examination of spectra. We find no correlation between iron abundance and distance from the cluster core, as might be inferred from recent photometric studies. NGC 3201 is the lowest mass halo cluster to date to contain stars with significantly different [Fe/H] values.

  3. Isotope Anomalies in the Fe-group Elements in Meteorites and Connections to Nucleosynthesis in AGB Stars

    NASA Astrophysics Data System (ADS)

    Wasserburg, G. J.; Trippella, O.; Busso, M.

    2015-05-01

    We study the effects of neutron captures in AGB stars on “Fe-group” elements, with an emphasis on Cr, Fe, and Ni. These elements show anomalies in 54Cr, 58Fe, and 64Ni in solar system materials, which are commonly attributed to supernovae (SNe). However, as large fractions of the interstellar medium (ISM) were reprocessed in AGB stars, these elements were reprocessed, too. We calculate the effects of such reprocessing on Cr, Fe, and Ni through 1.5 {{M}⊙ } and 3 {{M}⊙ } AGB models, adopting solar and 1/3 solar metallicities. All cases produce excesses of 54Cr, 58Fe, and 64Ni, while the other isotopes are little altered; hence, the observations may be explained by AGB processing. The results are robust and not dependent on the detailed initial isotopic composition. Consequences for other “Fe group” elements are then explored. They include 50Ti excesses and some production of 46,47,49Ti. In many circumstellar condensates, Ti quantitatively reflects these effects of AGB neutron captures. Scatter in the data results from small variations (granularity) in the isotopic composition of the local ISM. For Si, the main effects are instead due to variations in the local ISM from different SN sources. The problem of Ca is discussed, particularly with regard to 48Ca. The measured data are usually represented assuming terrestrial values for 42Ca/44Ca. Materials processed in AGB stars or sources with variable initial 42Ca/44Ca ratios can give apparent 48Ca excesses/deficiencies, attributed to SNe. The broader issue of galactic chemical evolution is also discussed in view of the isotopic granularity in the ISM.

  4. 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.

  5. 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.

  6. 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.

  7. The formation of aromatic molecules in heavily obscured post-AGB stars with O-rich masers

    NASA Astrophysics Data System (ADS)

    Garcia-Lario, Pedro; Garcia-Hernandez, Domingo Aníbal; Cernicharo, Jose; Perea-Calderon, Jose Vicente; Engels, Dieter

    2015-08-01

    We report Spitzer/IRS spectra of a small sample of heavily obscured and high mass loss post-AGB stars with O-rich maser emission. IRAM 30 m observations for two post-AGBs are also reported. The Spitzer/IRS spectra show the C-rich character of their circumstellar envelopes (CSE), as revealed by the presence of small hydrocarbon molecules such as C2H2, C4H2, C6H2, C6H6 , and HCN. Benzene (C6H6) is detected toward two sources in our sample, bringing up to three the total number of Galactic post-AGB objects where this molecule has been detected. The available IRAM 30 m data confirm that the central stars are C-rich, despite the presence of O-rich masers, and the presence of high velocity molecular outflows together with extreme mass loss rates (10-4 M⊙ yr-1). Our Spitzer and IRAM 30 m observations confirm the model of Cernicharo (2004) 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 large, complex carbon-rich molecules. This model also explain the presence of O-rich masers in C-rich post-AGB stars as a consequence of the extreme mass loss rate, being not necessary to invoke a chemistry change in their circumstellar envelopes.

  8. Stellar Evolution from AGB to Planetary Nebulae

    NASA Astrophysics Data System (ADS)

    Kwok, Sun

    2008-10-01

    Planetary nebulae are formed by an interacting winds process where the remnant of the AGB wind is compressed and accelerated by a later-developed fast wind from the central star. One-dimensional dynamical models have successfully explained the multi-shell (bubble, shell, crown, haloes) structures and the kinematics of planetary nebulae. However, the origin of the diverse asymmetric morphology of planetary nebulae is still not understood. Recent observations in the visible, infrared, and the submillimeter have suggested that the AGB mass loss becomes aspherical in the very late stages, forming an expanding torus around the star. A fast, highly collimated wind then emerges in the polar directions and carves out a cavity in the AGB envelope to form a bipolar nebula. Newly discovered structures such as concentric arcs, 2-D rings, multiple lobes, and point-symmetric structures suggest that both the slow and fast winds may have temporal and directional variations, and precession can play a role in the shaping of planetary nebulae. In this paper, we review the latest observations of planetary nebulae and proto-planetary nebulae and discuss the various physical mechanisms (rotation, binary, magnetic field, etc) that could lead to the observed morphologies.

  9. 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.

  10. The role of primary 16O as a neutron poison in AGB stars and fluorine primary production at halo metallicities.

    NASA Astrophysics Data System (ADS)

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

    The discovery of a historical bug in the s-post-process AGB code obtained so far by the Torino group forced us to reconsider the role of primary 16O in the 13C-pocket, produced by the 13C(alpha , n)16O reaction, as important neutron poison for the build up of the s-elements at Halo metallicities. The effect is noticeable only for the highest 13C-pocket efficiencies (cases ST*2 and ST). For Galactic disc metallicities, the bug effect is negligible. A comparative analysis of the neutron poison effect of other primary isotopes (12C, 22Ne and its progenies) is presented. The effect of proton captures, by 14N(n, p)14C, boosts a primary production of fluorine in halo AGB stars, with [F/Fe] comparable to [C/Fe], without affecting the s-elements production.

  11. 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.

  12. 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.

  13. 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…

  14. 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.

  15. Presenting Optical Spectra of AGB Stars in M31

    NASA Astrophysics Data System (ADS)

    Hamren, K.; Guhathakurta, P.; Toloba, E.; Dorman, C. E.; Seth, A. C.; Splash Collaboration; Phat Collaboration

    2015-08-01

    We present optical spectra of oxygen- and carbon-rich AGB stars in the disk of the Andromeda spiral galaxy (M31). Our AGB sample is drawn from the ˜10 000 stars covered by both the Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo (SPLASH) survey and the Panchromatic Hubble Andromeda Treasury (PHAT) survey. This dual coverage means that we have moderate resolution optical spectra taken with the DEIMOS spectrograph on the Keck II 10-m telescope, as well as six-filter HST photometry spanning the ultraviolet, optical and infrared. Our full AGB sample contains 143 carbon-rich AGB stars (C stars) and ˜1700 oxygen-rich AGB stars (M giants). We explore the spatial and kinematic distribution of these stars, the C/M ratio, spectral trends as a function of physical properties, and the fit to synthetic photometry.

  16. Detailed abundance study of four s-process enriched post-AGB stars in the Large Magellanic Cloud

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

    Context. The photospheric abundances of evolved solar-type stars of different metallicities serve as probes into stellar evolution theory. Aims: Stellar photospheres of post-asymptotic giant branch (post-AGB) stars bear witness to the internal chemical enrichment processes, integrated over their entire stellar evolution. Here we study post-AGB stars in the Large Magellanic Cloud (LMC). With their known distances, these rare objects are ideal tracers of AGB nucleosynthesis and dredge-up phenomena. Methods: We used the UVES spectrograph mounted on the Very Large Telescope at the European Southern Observatory, to obtain high-resolution spectra with high signal-to-noise of a sample of four post-AGB stars. The objects display a spectral energy distribution that indicates the presence of circumstellar dust. We perform a detailed abundance analysis on the basis of these spectra. Results: All objects are C-rich, and strongly enhanced in s-process elements. We deduced abundances of heavy s-process elements for all stars in the sample, and even found an indication of the presence of Hg in the spectrum of one object. The metallicity of all stars except J053253.51-695915.1 is considerably lower than the average value that is observed for the LMC. The derived luminosities show that we witness the late evolution of low-mass stars with initial masses close to 1 M⊙. An exception is J053253.51-695915.1 and we argue that this object is likely a binary. Conclusions: We confirmed the correlation between the efficiency of the third-dredge up and the neutron exposure that is detected in Galactic post-AGB stars. The non-existence of a correlation between metallicity and neutron irradiation is also confirmed and expanded to smaller metallicities. We confirm the status of 21 μm stars as post-carbon stars. Current theoretical AGB models overestimate the observed C/O ratios and fail to reproduce the variety of s-process abundance patterns that is observed in otherwise very similar objects

  17. Ultraviolet Properties of Galactic Globular Clusters with GALEX. I. The Color-Magnitude Diagrams

    NASA Astrophysics Data System (ADS)

    Schiavon, Ricardo P.; Dalessandro, Emanuele; Sohn, Sangmo T.; Rood, Robert T.; O'Connell, Robert W.; Ferraro, Francesco R.; Lanzoni, Barbara; Beccari, Giacomo; Rey, Soo-Chang; Rhee, Jaehyon; Rich, R. Michael; Yoon, Suk-Jin; Lee, Young-Wook

    2012-05-01

    We present Galaxy Evolution Explorer (GALEX) data for 44 Galactic globular clusters (GCs) obtained during three GALEX observing cycles between 2004 and 2008. This is the largest homogeneous data set on the UV photometric properties of Galactic GCs ever collected. The sample selection and photometric analysis are discussed, and color-magnitude diagrams (CMDs) are presented. The blue and intermediate-blue horizontal branch is the dominant feature of the UV CMDs of old Galactic GCs. Our sample is large enough to display the remarkable variety of horizontal branch shapes found in old stellar populations. Other stellar types that are obviously detected are blue stragglers and post-core-He burning stars. The main features of UV CMDs of Galactic GCs are briefly discussed. We establish the locus of post-core-He burning stars in the UV CMD and present a catalog of candidate asymptotic giant branch (AGB), AGB-manqué, post early-AGB, and post-AGB stars within our cluster sample. The authors dedicate this paper to the memory of co-author Bob Rood, a pioneer in the theory of the evolution of low-mass stars, and a friend, who sadly passed away on 2011 November 2.

  18. 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.

  19. 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.

  20. Dust in active galactic nuclei. Mid-infrared T-ReCS/Gemini spectra using the new RedCan pipeline

    NASA Astrophysics Data System (ADS)

    González-Martín, O.; Rodríguez-Espinosa, J. M.; Díaz-Santos, T.; Packham, C.; Alonso-Herrero, A.; Esquej, P.; Ramos Almeida, C.; Mason, R.; Telesco, C.

    2013-05-01

    Context. The unified model of active galactic nuclei (AGN) claims that the properties of AGN depend on the viewing angle of the observer with respect to a toroidal distribution of dust surrounding the nucleus. Both the mid-infrared (MIR) attenuation and continuum luminosity are expected to be related to dust associated with the torus. Therefore, isolating the nuclear component is essential for studying the MIR emission of AGN. Aims: This work is aimed at studying the MIR emission of AGN with the highest spatial resolution available to date, isolating its contribution from extended emission. We would like to address three fundamental questions: (1) how important is the AGN contribution to the MIR spectrum; (2) where dust attenuation arises; and (3) how does spatial resolution affect these issues. Methods: We compiled all the T-ReCS spectra (Gemini Observatory) available in the N-band for 22 AGN: 5 Type-1 and 17 Type-2 AGN. The high angular resolution of the T-ReCS spectra allowed us to probe physical regions of 57 pc (median). We used a novel pipeline called RedCan capable of producing flux- and wavelength-calibrated spectra for the CanariCam (GTC) and T-ReCS (Gemini) instruments. We measured the fine-structure [S IV] at 10.5 μm and the PAH at 11.3 μm line strengths, together with the silicate absorption/emission features. We also compiled Spitzer/IRS spectra to understand how spatial resolution influences the results. We complemented our sample with the results of 19 VISIR/VLT spectra (Paranal Observatory) and 20 nearby, highly obscured AGN (NH > 1.5 × 1024 cm-2) Spitzer spectra. Results: The 11.3 μm PAH feature is only clearly detected in the nuclear spectra of two AGN, while it is more common in the Spitzer data. For those two objects, the AGN emission in NGC 7130 accounts for more than 80% of the MIR continuum at 12 μm, while in the case of NGC 1808 the AGN does not dominate the MIR emission. This is confirmed by the correlation between the MIR and X

  1. On the internal pollution mechanisms in the globular cluster NGC 6121 (M4): heavy-element abundances and AGB models

    NASA Astrophysics Data System (ADS)

    D'Orazi, V.; Campbell, S. W.; Lugaro, M.; Lattanzio, J. C.; Pignatari, M.; Carretta, E.

    2013-07-01

    Globular clusters display significant variations in their light-element content, pointing to the existence of a second stellar generation formed from the ejecta of an earlier generation. The nature of these internal polluters is still a matter of debate: the two most popular scenarios indicate intermediate-mass asymptotic giant branch (IM-AGB) stars and fast rotating massive stars. Abundances determination for some key elements can help distinguish between these competitor candidates. We present in this paper Y abundances for a sample of 103 red giant branch stars in NGC 6121. Within measurement errors, we find that the [Y/Fe] is constant in this cluster contrary to a recent suggestion. For a subsample of six stars we also find [Rb/Fe] to be constant, consistent with previous studies showing no variation in other s-process elements. We also present a new set of stellar yields for IM-AGB stellar models of 5 and 6 M⊙, including heavy element s-process abundances. The uncertainties on the mass-loss rate, the mixing length parameter and the nuclear reaction rates have a major impact on the stellar abundances. Within the IM-AGB pollution scenario, the constant abundance of heavy elements inside the cluster requires a marginal s-process efficiency in IM-AGB stars. Such a constrain could still be satisfied by the present models assuming a stronger mass-loss rate. The uncertainties mentioned above are limiting the predictive power of IM-AGB models. For these reasons, at the moment we are not able to clearly rule out their role as main polluters of the second population stars in globular clusters.

  2. 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).

  3. 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

  4. High Resolution Spectroscopy of Post-AGB Stars: AGB Nucleosynthesis and Dredge-up

    NASA Astrophysics Data System (ADS)

    Reyniers, Maarten

    2002-12-01

    The final evolutionary stage of a low mass stellar object is a complex phase which is still poorly understood. In this thesis we contribute to a better understanding of the nucleosynthesis and dredge-up phenomena that occur in such objects during their ascent on the AGB by means of a detailed study of high-resolution optical spectra of post-AGB objects. In the first four chapters we mainly focus on the photospheric abundances of eight carbon and s-process enriched post-AGB objects. The carbon enrichment clearly proves that products of the helium burning shell were brought to the surface in the so-called third dredge-up. Moreover, also products of the (slow) neutron nucleosynthesis (the s-process) are brought to the surface, which allows us to characterize this nucleosynthesis. A detailed study of the chemical pattern displayed by these elements, including a comparison with up-to-date nucleosynthetic AGB stellar models, reveals that the expected anti-correlation between metallicity and neutron nucleosynthesis efficiency is hardly seen (if at all). The anti-correlation is expected since in a lower metallicity object, more neutrons are available per iron seed and hence heavier nucleons can be built up, assuming a similar primary production rate of the neutrons. Instead, a large spread in efficiency is seen. On the other hand, a clear correlation was found between the total enrichment and the nucleosynthesis efficiency, indicating that the dredge-up efficiency is strongly linked to the neutron production. Furthermore, detailed abundances of elements beyond the Ba-peak (Gd, Yb, Lu and possibly W) were obtained for the first time in intrinsically enriched objects for three stars of the sample, a result which was possible due to the combination of the high quality VLT+UVES spectra and newly released atomic data in both VALD and DREAM (Database on Rare Earths At Mons University). Finally, a new identification was found for the line at 670.8 nm in the spectra of the

  5. 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.

  6. SMA Observations of CO J=2-1 Emission from Evolved Stars in the Galactic Bulge

    NASA Astrophysics Data System (ADS)

    Sargent, Benjamin A.; Patel, N. A.; Meixner, M.; Otsuka, M.; Riebel, D.; Srinivasan, S.

    2013-01-01

    Asymptotic Giant Branch (AGB) stars are in the final stages of their lives, in which they eject mass. The dust grains formed in these mass outflows experience radiation pressure from the star and push the gas in the star's outflow away with the dust. There is much infrared data available to determine AGB dust mass loss in, e.g., the Milky Way and the Magellanic Clouds (e.g., the Surveying the Agents of a Galaxy's Evolution Spitzer Space Telescope Legacy project; PI: M. Meixner). However, the dependence of gas-to-dust ratios on metallicity for AGB stars, of use in determining total mass loss rates from optical and infrared observations constraining dust mass loss rates, is not well known. To remedy this, we present results from our 1.3 mm Submillimeter Array observations of 8 evolved stars in the inner Galactic Bulge (about 8 kpc distant). The metallicities of these OH/IR and AGB stars have been measured by others. We detect CO J=2-1 emission from OH 359.943+0.260. We possibly detect CO J=2-1 emission from [SLO2003] A12, though this detection is heavily contaminated by surrounding extended emission. We do not detect CO J=2-1 emission from the rest of our sample. Combining these CO data and analysis with observations at infrared wavelengths constraining dust mass loss, we determine the gas-to-dust ratios of Galactic Bulge stars for which CO emission is detected, determining a value of 320 for OH 359.943+0.260 and an upper limit of < 260 for [SLO2003] A12. We discuss applications of this work to studies of mass loss from evolved stars elsewhere, such as AGB stars in the Magellanic Clouds. We also discuss prospects for future CO observations of OH/IR and AGB stars in the Galactic Bulge.

  7. Dust production in supernovae and AGB stars

    NASA Astrophysics Data System (ADS)

    Matsuura, Mikako

    2015-08-01

    In the last decade, the role of supernovae on dust has changed; it has been long proposed that supernovae are dust destroyers, but now recent observations show that core-collapse supernovae can become dust factories. Theoretical models of dust evolution in galaxies have predicted that core-collapse supernovae can be an important source of dust in galaxies, if these supernovae can form a significant mass of dust (0.1-1 solar masses). The Herschel Space Observatory and ALMA detected dust in the ejecta of Supernova 1987A. They revealed an estimated 0.5 solar masses of dust. Herschel also found nearly 0.1 solar masses of dust in historical supernovae remnants, namely Cassiopeia A and the Crab Nebula. If dust grains can survive future interaction with the supernova winds and ambient interstellar medium, core-collapse supernovae can be an important source of dust in the interstellar media of galaxies. We further discuss the total dust mass injected by AGB stars and SNe into the interstellar medium of the Magellanic Clouds.

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

    NASA Astrophysics Data System (ADS)

    Ortiz, Roberto; Guerrero, Martín A.

    2016-09-01

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

  9. On the missing second generation AGB stars in NGC 6752

    NASA Astrophysics Data System (ADS)

    Cassisi, Santi; Salaris, Maurizio; Pietrinferni, Adriano; Vink, Jorick S.; Monelli, Matteo

    2014-11-01

    In recent years the view of Galactic globular clusters as simple stellar populations has changed dramatically, it is now thought that basically all globular clusters host multiple stellar populations, each with its own chemical abundance pattern and colour-magnitude diagram sequence. Recent spectroscopic observations of asymptotic giant branch stars in the globular cluster NGC 6752 have disclosed a low [Na/Fe] abundance for the whole sample, suggesting that they are all first generation stars, and that all second generation stars fail to reach the AGB in this cluster. A scenario proposed to explain these observations invokes strong mass loss in second generation horizontal branch stars - all located at the hot side of the blue and extended horizontal branch of this cluster - possibly induced by the metal enhancement associated to radiative levitation. This enhanced mass loss would prevent second generation stars from reaching the asymptotic giant branch phase, thus explaining at the same time the low value of the ratio between horizontal branch and asymptotic giant branch stars (the R2 parameter) observed in NGC 6752. We have critically discussed this mass-loss scenario, finding that the required mass-loss rates are of the order of 10-9 M⊙ yr-1, significantly higher than current theoretical and empirical constraints. By making use of synthetic horizontal branch simulations, we demonstrate that our modelling correctly predicts the R2 parameter for NGC 6752, without the need to invoke very efficient mass loss during the core He-burning stage. As a test of our stellar models we show that we can reproduce the observed value of R2 for both M 3, a cluster of approximately the same metallicity and with a redder horizontal branch morphology, and M 13, a cluster with a horizontal branch very similar to NGC 6752. However, our simulations for the NGC 6752 horizontal branch predict however the presence of a significant fraction of second generation stars (about 50%) along

  10. The AGB bump: a calibrator for core mixing

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    The efficiency of convection in stars affects many aspects of their evolution and remains one of the key-open questions in stellar modelling. In particular, the size of the mixed core in core-He-burning low-mass stars is still uncertain and impacts the lifetime of this evolutionary phase and, e.g., the C/O profile in white dwarfs. One of the known observables related to the Horizontal Branch (HB) and Asymptotic Giant Branch (AGB) evolution is the AGB bump. Its luminosity depends on the position in mass of the helium-burning shell at its first ignition, that is affected by the extension of the central mixed region. In this preliminary work we show how various assumptions on near-core mixing and on the thermal stratification in the overshooting region affect the luminosity of the AGB bump, as well as the period spacing of gravity modes in core-He-burning models.

  11. AGB circumstellar environments probed through the 21 cm atomic hydrogen line emission. A programme for the SKA?

    NASA Astrophysics Data System (ADS)

    Gerard, E.; Le Bertre, T.

    2006-06-01

    Red giant stars are responsible for 70% of the recycling of stellar matter in the local interstellar medium (ISM) through mass loss, mainly along the AGB sequence. Most of the matter in circumstellar shells is hydrogen in atomic (or molecular form). However, up to now, atomic hydrogen has remained largely undetected due to the weakness of its emission, the merging of circumstellar matter with the ambient ISM and the confusion from foreground and background interstellar hydrogen along the same line of sight. With the upgraded Nancay Radiotelescope, we have started a new search for HI at 21 cm towards AGB stars and post-AGBs, including PNs. We illustrate our results on one case, EP~Aqr, which shows that the contamination by interstellar emission must be treated with great care and discuss the prospects with the SKA. In order to sort out the genuine circumstellar HI emission from the interstellar one, it is necessary to map large areas of the sky (at all angular scales from sub-arcsec to degrees) with high spectral resolution, high sensitivity and a large dynamical range.

  12. Galactic Winds

    NASA Astrophysics Data System (ADS)

    Veilleux, Sylvain

    Galactic winds have become arguably one of the hottest topics in extragalactic astronomy. This enthusiasm for galactic winds is due in part to the detection of winds in many, if not most, high-redshift galaxies. Galactic winds have also been invoked by theorists to (1) suppress the number of visible dwarf galaxies and avoid the "cooling catastrophe" at high redshift that results in the overproduction of massive luminous galaxies, (2) remove material with low specific angular momentum early on and help enlarge gas disks in CDM + baryons simulations, (3) reduce the dark mass concentrations in galaxies, (4) explain the mass-metallicity relation of galaxies from selective loss of metal-enriched gas from smaller galaxies, (5) enrich and "preheat" the ICM, (6) enrich the IGM without disturbing the Lyαforest significantly, and (7) inhibit cooling flows in galaxy clusters with active cD galaxies. The present paper highlights a few key aspects of galactic winds taken from a recent ARAA review by Veilleux, Cecil, &Bland-Hawthorn (2005; herafter VCBH). Readers interested in a more detailed discussion of this topic are encouraged to refer to the original ARAA article.

  13. 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.

  14. Diffuse Galactic light at high Galactic latitude: nature and interpretation

    NASA Astrophysics Data System (ADS)

    Zagury, Frédéric

    2006-08-01

    The hypothesis of an extended red emission (ERE) in diffuse Galactic light (DGL) has been put forward in 1998 by Gordon, Witt & Friedmann who found that scattered starlight was not enough to explain the amount of DGL in the R band, in some high Galactic latitude directions. This paper re-investigates, for high Galactic latitudes, the brightnesses and colours of DGL, integrated star and galaxy light (ISGL), and of the total extrasolar light (ISGL+DGL) measured by Pioneer. Under the traditional assumption that DGL is forward scattering of background starlight by interstellar dust on the line of sight, ISGL and Pioneer have very close colours, as it is found by Gordon, Witt & Friedmann. Pioneer observations at high |b| thus accept an alternative and simple interpretation, with no involvement of ERE in DGL.

  15. 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…

  16. 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.

  17. 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.

  18. Cool Bottom Processing on the AGB and Presolar Grain Compositions

    NASA Technical Reports Server (NTRS)

    Nollett, Kenneth M.; Busso, M.; Wasserburg, G. J.

    2002-01-01

    We describe results from a model of cool bottom processing (CBP) in AGB (asymptotic giant branch) stars. We predict O, Al, C and N isotopic compositions of circumstellar grains. Measured compositions of mainstream SiC grains and many oxide grains are consistent with CBP. Additional information is contained in the original extended abstract.

  19. Milky Way red dwarfs in the BoRG survey; galactic scale-height and the distribution of dwarf stars in WFC3 imaging

    SciTech Connect

    Holwerda, B. W.; Bouwens, R.; Trenti, M.; Clarkson, W.; Sahu, K.; Bradley, L.; Stiavelli, M.; Pirzkal, N.; Ryan, R.; De Marchi, G.; Andersen, M.

    2014-06-10

    -redshift galaxies. The relative ubiquity of M-dwarfs however will make them ideal tracers of Galactic halo substructure with EUCLID and reference stars for James Webb Space Telescope observations.

  20. 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

  1. 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

  2. Carbon Stars in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Totten, E. J.; Irwin, M. J.

    1996-04-01

    A byproduct of the APM high redshift quasar survey (Irwin et al. 1991) was the discovery of ~ 20 distant (20-100kpc) cool AGB carbon stars (all N-type) at high Galactic latitude. In August we used the INT+IDS to survey the rest of the high latitude SGC sky visible from La Palma and found 10 more similar carbon stars. Before this work there were only a handful of published faint high latitude cool carbon stars known (eg. Margon et al., 1984, Mould et al., 1985) and there has been speculation as to their origin (eg. Sanduleak, 1980, van den Bergh & Lafontaine, 1984). Intermediate age carbon stars (3 -- 7 Gyrs) seem unlikely to have formed in the halo in isolation from other star forming regions so how did they get there ? One possiblity that we are investigating, is that they arise from either the disruption of tidally captured dSph galaxies or are a manifestion of the long sought after optical component of the Magellanic Stream. Lack of proper motion rules out the possibility of them being dwarf carbon stars (eg. Warren et al., 1992); indeed no N-type carbon stars have been found to be dwarf carbon stars. Our optical spectroscopy confirms their carbon star type (they are indistinguishable from cool AGB carbon stars in nearby dwarf galaxies) and hence probable large distances. We are extending our survey to the NGC region, obtaining radial velocities and good S:N fluxed spectra for all the carbon stars. This will enable us to investigate their kinematics, true spatial distribution and hence their origin. Even, in the event that these objects are somehow an integral part of the Galactic halo, then their velocities and large distances will enable direct studies of the velocity ellipsoid and rotation of the outer halo (eg. Green et al., 1994).

  3. 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.

  4. Galactic Evolution

    NASA Astrophysics Data System (ADS)

    Brekke, Stewart

    2013-04-01

    All galaxies began as spiral galaxies. The early universe began with sets of two or more pre-galactic arms orbiting each other. As gravitational attraction between the arms took effect, the fore-sections of the arms tangentially collided forming spiral galaxies when they attached with the orbital motion of the arms being converted to the rotational motion of the newly formed spiral galaxies or (Iφ)arm1+ (Iφ)arm2+ ...+ (Iφ)armn= (Iφ)galaxy. If the centripetal force on the arms is more than the gravitational force on the arms, the spiral galaxy remains a spiral galaxy i.e. mv^2/r>=Gmarmmgalaxy/r^2. If the galaxy is slowly rotating, the spiral arms collapse into the body of the galaxy because the gravitational force is greater than the centripetal force on the arms and an elliptical galaxy is formed i.e. mv^2/r < Gmarmsmgalaxy/r^2.

  5. H2O Formation in C-rich AGB Winds

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

    The Herschel detection of warm H2O vapor emission from C-rich winds of AGB stars challenges the current understanding of circumstellar chemistry. Two mechanisms have been invoked to explain warm H2O formation. In the first, penetration of UV interstellar radiation through a clumpy circumstellar medium causes the formation of H2O molecules in the inner envelope. In the second, periodic shocks passing through the medium immediately above the stellar surface lead to H2O formation. We have identified H2O emission trends from distance-independent line-strength ratios in a sample of 18 C-rich AGB sources, by comparing to a theoretical model grid. We detect warm H2O emission close to or inside the acceleration zone of all sample stars. We find an anti-correlation between the H2O/CO line-strength ratios and the mass-loss rate for Mgas>3×10-7 M⊙/yr. This implies that the H2O formation mechanism becomes less efficient with increasing envelope column density. The anti-correlation breaks down for SRb objects, which clump together at an overall lower H2O abundance. Finally, a radial dependence of the H2O abundance within individual sources is unlikely. These findings lend support to shock-induced non-equilibrium chemistry as the primary source of H2O formation in C-rich AGB stars.

  6. 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

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  8. 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.

  9. Observing the next galactic supernova

    SciTech Connect

    Adams, Scott M.; Kochanek, C. S.; Beacom, John F.; Stanek, K. Z.; Vagins, Mark R.

    2013-12-01

    No supernova (SN) in the Milky Way has been observed since the invention of the optical telescope, instruments for other wavelengths, neutrino detectors, or gravitational wave observatories. It would be a tragedy to miss the opportunity to fully characterize the next one. To aid preparations for its observations, we model the distance, extinction, and magnitude probability distributions of a successful Galactic core-collapse supernova (ccSN), its shock breakout radiation, and its massive star progenitor. We find, at very high probability (≅ 100%), that the next Galactic SN will easily be detectable in the near-IR and that near-IR photometry of the progenitor star very likely (≅ 92%) already exists in the Two Micron All Sky Survey. Most ccSNe (98%) will be easily observed in the optical, but a significant fraction (43%) will lack observations of the progenitor due to a combination of survey sensitivity and confusion. If neutrino detection experiments can quickly disseminate a likely position (∼3°), we show that a modestly priced IR camera system can probably detect the shock breakout radiation pulse even in daytime (64% for the cheapest design). Neutrino experiments should seriously consider adding such systems, both for their scientific return and as an added and internal layer of protection against false triggers. We find that shock breakouts from failed ccSNe of red supergiants may be more observable than those of successful SNe due to their lower radiation temperatures. We review the process by which neutrinos from a Galactic ccSN would be detected and announced. We provide new information on the EGADS system and its potential for providing instant neutrino alerts. We also discuss the distance, extinction, and magnitude probability distributions for the next Galactic Type Ia supernova (SN Ia). Based on our modeled observability, we find a Galactic ccSN rate of 3.2{sub −2.6}{sup +7.3} per century and a Galactic SN Ia rate of 1.4{sub −0.8}{sup +1.4} per

  10. 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.

  11. 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.

  12. Stellar Evolution with Rotation: Mixing Processes in AGB Stars

    NASA Astrophysics Data System (ADS)

    Driebe, T.; Blöcker, T.

    We included diffusive angular momentum transport and rotationally induced mixing processes in our stellar evolution code and studied the influence of rotation on the evolution of intermediate mass stars (M*=2dots6 Msolar) towards and along the asymptotic giant branch (AGB). The calculations start in the fully convective pre-main sequence phase and the initial angular momentu m was adjusted such that on the zero-age main sequence vrot=200 km/ s is achieved. The diffusion coefficients for the five rotational instabilities considered (dynamical shear, secular shear, Eddington-Sweet (ES) circulation, Solberg-Høiland-instability and Goldreich-Schubert-Fricke (GSF) instability) were adopted from Heger et al. (2000, ApJ 528, 368). Mixing efficiency and sensitivity of these processes against molecular weight gradients have been determined by calibration of the main sequence width. In this study we focus on the abundance evolution of carbon. On the one hand, the surface abundance ratios of 12C/13C a nd 12C/16O at the base of the AGB were found to be ≈ 7dots 10 and ≈ 0.1, resp., being a factor of two lower than in non-rotating models. This results from the slow but continuously operating rotationally induced mixing due to the ES-circulation and the GSF-instability during the long main sequence phase. On the other hand, 13C serves as neutron source for interior s-process nucleosynthesis in AGB stars vi a 13C(α,n)16O. Herwig et al. (1997, A&A 324, L81) found that a 13C pocket is forme d in the intershell region of 3 Msolar AGB star if diffusive overshoot is considered. Our calculations show, that mixing processes due to rotation open an alternative channel for the formation of a 13C pocket as found by Langer et al. (1999, A&A 346, L37). Again, ES-circulation and GSF-instability are the predominant rotational mixing processes.

  13. 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).

  14. Leadership in Governance: The View from AGB's Current and Former Board Chairs

    ERIC Educational Resources Information Center

    Trusteeship, 2010

    2010-01-01

    The challenges with which college and university boards must grapple promise to become only more complex in the coming years, placing ever-greater demands on the leaders of those boards. This article presents a conversation between Association of Governing Boards of Universities and Colleges (AGB) President Richard D. Legon and two AGB leaders who…

  15. THE ABUNDANCE OF FLUORINE IN NORMAL G AND K STARS OF THE GALACTIC THIN DISK

    SciTech Connect

    Pilachowski, C. A.; Pace, Cameron E-mail: cjamespace@gmail.com

    2015-09-15

    The abundance of fluorine is determined from the (2-0) R9 2.3358 μm feature of the molecule HF for several dozen normal G and K stars in the Galactic thin disk from spectra obtained with the Phoenix IR spectrometer on the 2.1 m telescope at Kitt Peak. The abundances are analyzed in the context of Galactic chemical evolution to explore the contributions of supernovae and asymptotic giant branch (AGB) stars to the abundance of fluorine in the thin disk. The average abundance of fluorine in the thin disk is found to be [F/Fe] = +0.23 ± 0.03, and the [F/Fe] ratio is flat or declines slowly with metallicity in the range from –0.6 < [Fe/H] < +0.3, within the limits of our estimated uncertainty. The measured abundance of fluorine and lack of variation with metallicity in Galactic thin disk stars suggest neutrino spallation in Type II supernovae contributes significantly to the Galactic fluorine abundance, although contributions from AGB stars may also be important.

  16. 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.

  17. Mass-loss on the red giant branch: the value and metallicity dependence of Reimers' η in globular clusters

    NASA Astrophysics Data System (ADS)

    McDonald, I.; Zijlstra, A. A.

    2015-03-01

    The impact of metallicity on the mass-loss rate from red giant branch (RGB) stars is studied through its effect on the parameters of horizontal branch (HB) stars. The scaling factors from Reimers and Schröder and Cuntz are used to measure the efficiency of RGB mass-loss for typical stars in 56 well-studied Galactic globular clusters (GCs). The median values among clusters are, respectively, η _R = 0.477 ± 0.070 ^{+0.050}_{-0.062} and η _SC = 0.172 ± 0.024 ^{+0.018}_{-0.023} (standard deviation and systematic uncertainties, respectively). Over a factor of 200 in iron abundance, η varies by ≲30 per cent, thus mass-loss mechanisms on the RGB have very little metallicity dependence. Any remaining dependence is within the current systematic uncertainties on cluster ages and evolution models. The low standard deviation of η among clusters (≈14 per cent) contrasts with the variety of HB morphologies. Since η incorporates cluster age, this suggests that age accounts for the majority of the `second parameter problem', and that a Reimers-like law provides a good mass-loss model. The remaining spread in η correlates with cluster mass and density, suggesting helium enrichment provides the third parameter explaining HB morphology of GCs. We close by discussing asymptotic giant branch (AGB) mass-loss, finding that the AGB tip luminosity is better reproduced and η has less metallicity dependence if GCs are more co-eval than generally thought.

  18. Post-AGB stars in the SMC as tracers of stellar evolution: the extreme s-process enrichment of the 21 μm star J004441.04-732136.4

    NASA Astrophysics Data System (ADS)

    De Smedt, K.; Van Winckel, H.; Karakas, A. I.; Siess, L.; Goriely, S.; Wood, P. R.

    2012-05-01

    Context. This paper is part of a larger project in which we want to focus on the still poorly understood asymptotic giant branch (AGB) third dredge-up processes and associated s-process nucleosynthesis. Aims: We confront accurate spectral abundance analyses of post-AGB stars in both the Magellanic Clouds, to state-of-the-art AGB model predictions. With this comparison we aim at improving our understanding of the 3rd dredge-up phenomena and their dependencies on initial mass and metallicity. Methods: Because of the well constrained distance with respect to Galactic post-AGB stars, we choose an extra-galactic post-AGB star for this contribution, namely the only known 21 μm object of the Small Magellanic Cloud (SMC): J004441.04-732136.4. We used optical UVES spectra to perform an accurate spectral abundance analysis. With photometric data of multiple catalogues we construct a spectral energy distribution (SED) and perform a variability analysis. The results are then compared to predictions of tailored theoretical chemical AGB evolutionary models for which we used two evolution codes. Results: Spectral abundance results reveal J004441.04-732136.4 to be one of the most s-process enriched objects found up to date, while the photospheric C/O ratio of 1.9 ± 0.7, shows the star is only modestly C-rich. J004441.04-732136.4 also displays a low [Fe/H] = -1.34 ± 0.32, which is significantly lower than the mean metallicity of the SMC. From the SED, a luminosity of 7600 ± 200 L⊙ is found, together with E(B - V) = 0.64 ± 0.02. According to evolutionary post-AGB tracks, the initial mass should be ≈1.3 M⊙. The photometric variability shows a clear period of 97.6 ± 0.3 days. The detected C/O as well as the high s-process overabundances (e.g. [Y/Fe] = 2.15, [La/Fe] = 2.84) are hard to reconcile with the predictions. The chemical models also predict a high Pb abundance, which is not compatible with the detected spectrum, and a very high 12C/13C, which is not yet constrained

  19. 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.

  20. Binarity and Accretion: X-Ray Emission from AGB stars with FUV Excesses

    NASA Astrophysics Data System (ADS)

    Sahai, Raghvendra

    2012-10-01

    We propose a pilot survey for X-ray emission from AGB stars that are candidates for having binary companions with active accretion. These objects were identified via our innovative technique to search for FUV/NUV excesses in AGB stars using GALEX. The detection (or non-detection) of X-rays from this sample will enable us to begin testing models for the origin of the UV-excesses, leading to vital breakthroughs in our understanding of accretion-related phenomena and binarity in AGB stars. A larger survey, optimised using results fron this study, will be proposed in future cycles.

  1. Where Galactic Snakes Live

    NASA Technical Reports Server (NTRS)

    2006-01-01

    This infrared image from NASA's Spitzer Space Telescope shows what astronomers are referring to as a 'snake' (upper left) and its surrounding stormy environment. The sinuous object is actually the core of a thick, sooty cloud large enough to swallow dozens of solar systems. In fact, astronomers say the 'snake's belly' may be harboring beastly stars in the process of forming.

    The galactic creepy crawler to the right of the snake is another thick cloud core, in which additional burgeoning massive stars might be lurking. The colorful regions below the two cloud cores are less dense cloud material, in which dust has been heated by starlight and glows with infrared light. Yellow and orange dots throughout the image are monstrous developing stars; the red star on the 'belly' of the snake is 20 to 50 times as massive as our sun. The blue dots are foreground stars.

    The red ball at the bottom left is a 'supernova remnant,' the remains of massive star that died in a fiery blast. Astronomers speculate that radiation and winds from the star before it died, in addition to a shock wave created when it exploded, might have played a role in creating the snake.

    Spitzer was able to spot the two black cloud cores using its heat-seeking infrared vision. The objects are hiding in the dusty plane of our Milky Way galaxy, invisible to optical telescopes. Because their heat, or infrared light, can sneak through the dust, they first showed up in infrared images from past missions. The cloud cores are so thick with dust that if you were to somehow transport yourself into the middle of them, you would see nothing but black, not even a star in the sky. Now, that's spooky!

    Spitzer's new view of the region provides the best look yet at the massive embryonic stars hiding inside the snake. Astronomers say these observations will ultimately help them better understand how massive stars form. By studying the clustering and range of masses of the stellar embryos, they hope

  2. Erratum: “Milky Way Red Dwarfs in the Borg Survey; Galactic Scale-Height and the Distribution of Dwarfs Stars in WFC3 Imaging" (2014, ApJ, 788, 77)

    NASA Astrophysics Data System (ADS)

    Holwerda, B. W.; Trenti, M.; Clarkson, W.; Sahu, K.; Bradley, L.; Stiavelli, M.; Pirzkal, N.; De Marchi, G.; Andersen, M.; Bouwens, R.; Ryan, R.; van Vledder, I.; van der Vlugt, D.

    2016-07-01

    In the catalog of M-dwarfs presented in Holwerda et al. (2014, H14 hereafter), there is an issue with the conversion from celestial coordinates to Galactic ones, done with pyephem a wrapper around a trusted and vetted library ephermis. Here we present the corrected coordinates (using AstroPy) and distances based on AB magnitudes. We have amended the tables and figures accordingly. The relation between vertical scale-height (z0) and M- dwarf subtype found in H14 is no longer present. We find a scale-height of 600 pc for all types, in part due to the presence of a second Galactic structural component.

  3. The distances of the Galactic novae

    NASA Astrophysics Data System (ADS)

    Özdönmez, Aykut; Güver, Tolga; Cabrera-Lavers, Antonio; Ak, Tansel

    2016-09-01

    Utilizing the unique location of red clump giants on colour-magnitude diagrams obtained from various near-infrared surveys, we derived specific reddening-distance relations towards 119 Galactic novae for which independent reddening measurements are available. Using the derived distance-extinction relation and the independent measurements of reddening we calculated the most likely distances for each system. We present the details of our distance measurement technique and the results of this analysis, which yielded the distances of 73 Galactic novae and allowed us to set lower limits on the distances of 46 systems. We also present the reddening-distance relations derived for each nova, which may be useful to analyse the different Galactic components present in the line of sight.

  4. The Galactic disc distribution of planetary nebulae with warm dust emission features - II

    NASA Astrophysics Data System (ADS)

    Casassus, S.; Roche, P. F.

    2001-02-01

    We address the question of whether the distribution of warm-dust compositions in IR-bright Galactic disc PNe (Paper I, Casassus et al.) can be linked to the underlying stellar population. The PNe with warm dust emission represent a homogeneous population, which is presumably young and minimally affected by a possible dependence of PN lifetime on progenitor mass. The sample in Paper I thus allows testing of the predictions of single-star evolution, through a comparison with synthetic distributions and under the assumption that tip-of-the-AGB and PN statistics are similar. We construct a schematic model for AGB evolution (adapted from Groenewegen & de Jong), the free parameters of which are calibrated with the luminosity function (LF) of C stars in the LMC, the initial-final mass relation and the range of PN compositions. The observed metallicity gradient and distribution of star-forming regions with Galactocentric radius (Bronfman et al.) allow us to synthesize the Galactic disc PN progenitor population. We find that the fraction of O-rich PNe, f(0), is a tight constraint on AGB parameters. For our best model, a minimum PN progenitor mass Mmin=1 M⊙ predicts that about 50per cent of all young PNe should be O-rich, compared with an observed fraction of 22per cent; thus Mmin=1.2 M⊙, at a 2σ confidence level Mmin=1.3 M⊙ at 1σ). By contrast, current AGB models for single stars can account neither for the continuous range of N enrichment (Leisy & Dennefeld) nor for the observation that the majority of very C-rich PNe have Peimbert type I (Paper I). f(O) is thus an observable quantity much easier to model. The decrease in f(O) with Galactocentric radius, as reported in Paper I, is a strong property of the synthetic distribution, independent of Mmin. This trend reflects the sensitivity of the surface temperature of AGB stars and of the core mass at the first thermal pulse to the Galactic metallicity gradient.

  5. SPIRITS: SPitzer InfraRed Intensive Transients Survey

    NASA Astrophysics Data System (ADS)

    Kasliwal, Mansi; Cao, Yi; Masci, Frank; Helou, George; Williams, Robert; Bally, John; Bond, Howard; Whitelock, Patricia; Cody, Ann Marie; Gehrz, Robert; Jencson, Jacob; Tinyanont, Samaporn; Smith, Nathan; Surace, Jason; Armus, Lee; Cantiello, Matteo; Langer, Norbert; Levesque, Emily; Mohamed, Shazrene; Ofek, Eran; Parthasarathy, Mudumba; van Dyk, Schuyler; Boyer, Martha; Phillips, Mark; Hsiao, Eric; Morrell, Nidia; Perley, Dan; Gonzalez, Consuelo; Contreras, Carlos

    2014-12-01

    The exploration of the dynamic mid-infrared sky has just begun. We propose to continue the SPitzer InfraRed Intensive Transients Survey (SPIRITS) --- a systematic search of 194 nearby galaxies within 20 Mpc, on timescales ranging between a week to a year, to a depth of 20 mag. During Cycle 10, SPIRITS has discovered over 40 infrared transients and over 1200 infrared variables. We are discovering explosive transients (ILRT, LRN, CNe, SNe), eruptive variables (LBV, RSG, YSG, AGB), and mysterious new infrared events devoid of optical counterparts (e.g. possible birth of a massive star system). Our Cycle 10 discoveries motivate our experiment design for Cycle 11 and 12. In particular, we request additional shorter cadence baselines to fill in missing pieces in our understanding of the end points of stellar evolution. Three years of SPIRITS will constitute the definitive study to ascertain the rate and origin of new classes of infrared transients, quantify the contribution of classical novae to galactic chemical evolution, and uncover supernovae buried in starbursts. We are also systematically probing mass-loss rates and dust formation in the most massive stars. SPIRITS yields a census of supergiant variability and asymptotic giant branch variability in diverse galaxy environments. The SPIRITS team continues to be committed to a concomitant ground-based NIR and optical survey and extensive spectroscopic follow-up: 308 nights of near-IR imaging, 135 nights of optical imaging and 34 nights of spectroscopy in Cycle 11 and 12. Follow-up will serve to maximize the discovery potential of our requested 795.3 hrs of Spitzer/IRAC and 10 orbits of HST/WFC3 observing time.

  6. Chemical abundances in Galactic planetary nebulae with Spitzer spectra

    NASA Astrophysics Data System (ADS)

    García-Hernández, D. A.; Górny, S. K.

    2014-07-01

    We present new low-resolution (R ~ 800) optical spectra of 22 Galactic planetary nebulae (PNe) with Spitzer spectra. These data are combined with recent optical spectroscopic data available in the literature to construct representative samples of compact (and presumably young) Galactic disc and bulge PNe with Spitzer spectra. Attending to the nature of the dust features - C-rich, O-rich, and both C- and O-rich dust features (or double chemistry) - seen in their Spitzer spectra, the Galactic disc and bulge PNe are classified according to four major dust types (oxygen chemistry or OC, carbon chemistry or CC, double chemistry or DC, featureless or F) and subtypes (amorphous and crystalline, and aliphatic and aromatic), and their Galactic distributions are presented. Nebular gas abundances of He, N, O, Ne, S, Cl, and Ar, as well as plasma parameters (e.g. Ne, Te) are homogeneously derived by using the classical empirical method. We study the median chemical abundances and nebular properties in Galactic disc and bulge PNe depending on their Spitzer dust types and subtypes. The differences and similarities between PNe in the Galactic disc and bulge are reported. In particular, the median abundances for the major Spitzer dust types CC and OC are representative of the dominant dust subtype (which are different in both Galactic environments), while these values in DC PNe are representative of the two DC subtypes. A comparison of the derived median abundance patterns with AGB nucleosynthesis predictions mainly show that i) DC PNe, both with amorphous and crystalline silicates, display high-metallicity (solar/supra-solar) and the highest He abundances and N/O abundance ratios, suggesting relatively massive (~3-5 M⊙) hot bottom burning AGB stars as progenitors; ii) PNe with O-rich and C-rich unevolved dust (amorphous and aliphatic) seem to evolve from subsolar metallicity (z ~ 0.008) and lower mass (<3 M⊙) AGB stars; iii) a few O-rich PNe and a significant fraction of C

  7. The European Galactic Plane Surveys: EGAPS

    NASA Astrophysics Data System (ADS)

    Groot, P. J.; Drew, J.; Greimel, R.; Gaensicke, B.; Knigge, C.; Irwin, M.; Mampaso, A.; Augusteijn, T.; Morales-Rueda, L.; Barlow, M.; Iphas Collaboration; Uvex Collaboration; Vphas+ Collaboration

    2006-08-01

    Introduction: The European Galactic Plane Surveys (EGAPS) will for the first time ever map the complete galactic plane (10x360 degrees) down to 21st magnitude in u', g', r', i' and H-alpha and partly in He I 5875. It will complete a database of ~1 billion objects. The aim of EGAPS is to study populations of short-lived stellar and binary phases in our Galaxy and combine these population studies with stellar and binary evolutionary codes to vastly improve our understanding of crucial phases of stellar evolution. Target populations include Wolf-Rayet stars, planetary nebulae, white dwarfs (in binaries), cataclysmic variables and other mass-transferring binaries. Methods: EGAPS is using the INT+WFC on La Palma for the Northern Hemisphere and will use the VST+Omegacam in the Southern Hemisphere. Results: The Northern red survey (IPHAS, using r', i', and Halpha) has started in 2003 and is currently 70% complete. The northern blue survey (UVEX; u',g',r' and HeI) has started in June 2006. Results include the detection of a number of rare planetary nebulae, cataclysmic variables, red-dwarf white dwarf binaries in clusters, a possible AM CVn candidate, and a deep photometric and spectroscopic investigation of the Cyg X region. Discussion: EGAPS will revolutionize the field of galactic stellar astrophysics by completing the first ever digital, multicolour survey of the Galactic Plane.

  8. Discovery in the Galactic Bulge

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-11-01

    In our efforts to map our galaxys structure, one region has remained very difficult to probe: the galactic center. A new survey, however, uses infrared light to peer through the gas and dust in the galactic plane, searching for variable stars in the bulge of the galaxy. This study has discovered a population of very young stars in a thin disk in the galactic center, providing clues to the star formation history of the Milky Way over the last 100 million years.Obscured CenterThe center of the Milky Way is dominated by a region known as the galactic bulge. Efforts to better understand this region in particular, its star formation history have been hindered by the stars, gas, and dust of the galactic disk, which prevent us from viewing the galactic bulge at low latitudes in visible light.The positions of the 35 classical Cepheids discovered in VVV data, projected onto an image of the galactic plane. Click for a better look! The survey area is bounded by the blue lines, and the galactic bar is marked with a red curve. The bottom panel shows the position of the Cepheids overlaid on the VVV bulge extinction map. [Dkny et al. 2015]Infrared light, however, can be used to probe deeper through the dust than visible-light searches. A new survey called VISTA Variables in the Via Lactea (VVV) uses the VISTA telescope in Chile to search, in infrared, for variable stars in the inner part of the galaxy. The VVV survey area spans the Milky Way bulge and an adjacent section of the mid-plane where star formation activity is high.Led by Istvn Dkny, a researcher at the Millennium Institute of Astrophysics and the Pontifical Catholic University of Chile, a team has now used VVV data to specifically identify classical Cepheid variable stars in the bulge. Why? Cepheids are pulsating stars with a very useful relation between their periods and luminosities that allows them to be used as distance indicators. Moreover, classical Cepheids are indicators of young stellar populations which can

  9. The FLAMINGOS-2 Galactic Center Survey

    NASA Astrophysics Data System (ADS)

    Raines, Steven N.; Flamingos-2 Galactic Center Survey Team

    2010-03-01

    The FLAMINGOS-2 instrument achieved high-quality first-light observations on the Gemini South telescope in September 2009 and is undergoing further testing and scientific commissioning into early 2010. Based on the results so far, FLAMINGOS-2 (F2) on the Gemini 8-meter telescope is an extremely powerful wide-field near-infrared imager and multi-object spectrograph. In order to take best advantage of the strengths of F2 early in its life cycle, we propose to use 21 nights of Gemini guaranteed time in 3 surveys - the FLAMINGOS-2 Early Science Surveys (F2ESS). The F2ESS will encompass 3 corresponding scientific themes - the Galactic Center, extragalactic astronomy, and star formation. In particular, the Galactic Center Survey will identify the IR couterparts to several hundred new X-ray binaries in the Galactic Center. This will allow us to identify the nature of the mysterious Chandra source population in the Galactic Center and provide tremendous opportunities for multi-wavelength follow-up observations. In addition, the "by-catch" of this survey will be a catalog of several thousand red giant branch stars with accurate spectroscopy -- these can be used to measure the star formation history of the Galactic Center and thus constrain the mass evolution history of the supermassive black hole in Sgr A*. In this poster, I review the plans for carrying out this survey with F2, data analysis plans and software, and the expected scientific impact from this powerful new observational tool.

  10. Galactic Halos of Hydrogen

    NASA Technical Reports Server (NTRS)

    2005-01-01

    This image shows two companion galaxies, NGC 4625 (top) and NGC 4618 (bottom), and their surrounding cocoons of cool hydrogen gas (purple). The huge set of spiral arms on NGC 4625 (blue) was discovered by the ultraviolet eyes of NASA's Galaxy Evolution Explorer. Though these arms are nearly invisible when viewed in optical light, they glow brightly in ultraviolet. This is because they are bustling with hot, newborn stars that radiate primarily ultraviolet light.

    The vibrant spiral arms are also quite lengthy, stretching out to a distance four times the size of the galaxy's core. They are part of the largest ultraviolet galactic disk discovered so far.

    Astronomers do not know why NGC 4625 grew arms while NGC 4618 did not. The purple nebulosity shown here illustrates that hydrogen gas - an ingredient of star formation - is diffusely distributed around both galaxies. This means that other unknown factors led to the development of the arms of NGC 4625.

    Located 31 million light-years away in the constellation Canes Venatici, NGC 4625 is the closest galaxy ever seen with such a young halo of arms. It is slightly smaller than our Milky Way, both in size and mass. However, the fact that this galaxy's disk is forming stars very actively suggests that it might evolve into a more massive and mature galaxy resembling our own.

    The image is composed of ultraviolet, visible-light and radio data, from the Galaxy Evolution Explorer, the California Institute of Technology's Digitized Sky Survey, and the Westerbork Synthesis Radio Telescope, the Netherlands, respectively. Near-ultraviolet light is colored green; far-ultraviolet light is colored blue; and optical light is colored red. Radio emissions are colored purple.

  11. Active galactic nuclei

    PubMed Central

    Fabian, Andrew C.

    1999-01-01

    Active galactic nuclei are the most powerful, long-lived objects in the Universe. Recent data confirm the theoretical idea that the power source is accretion into a massive black hole. The common occurrence of obscuration and outflows probably means that the contribution of active galactic nuclei to the power density of the Universe has been generally underestimated. PMID:10220363

  12. Wide-field Monitoring of the Galactic Plane in the K- and the H-band

    NASA Astrophysics Data System (ADS)

    Yanagisawa, K.; Nakada, Y.; Izumiura, H.; Watanabe, E.; Shimizu, Y.; Okada, N.; Okita, K.; Norimoto, K.; Okata, T.; Koyano, H.; Yoshida, M.

    The Okayama Astrophysical Observatory of NAOJ started the monitoring program of mass-losing AGB stars using an imaging camera named Okayama Astrophysical Observatory Wide Field Camera. The fast optics yields a field of view of 1¡ß1 deg2 and the pixel resolution of 2 arcsec at the focus of the 91-cm telescope. A HAWAII2 array will be installed inside the camera reaching the limiting magnitude of K=13 with a 45-s exposure. In 2003 the monitoring will start covering the Galactic plane from l=0 to 270 deg every three weeks.

  13. Constraints on Galactic Center Activity: A Search for Enhanced Galactic Center Lithium and Boron

    NASA Astrophysics Data System (ADS)

    Lubowich, D. A.; Turner, B. E.; Hobbs, L. M.

    1998-12-01

    The abundances of lithium and boron provide important information about big bang nucleosynthesis, Galactic chemical evolution, stellar evolution, and cosmic-ray spallation reactions. We conducted the first search for the ground-state hyperfine-structure transitions of Li I (2S1/2; F = 2-1 803 MHz) and B I (2P1/2; F = 2-1 732 MHz). We used the 43 m NRAO radio telescope to search for enhanced Galactic center (GC) Li and B expected from models of Galactic activity. We did not detect Li I or B I and obtained upper limits of N(Li I) < 1.9 × 1016 cm-2, (Li/H) < 3.9 × 10-8, N(B I) < 2.2 × 1018 cm-2, and (B/H) < 9.2 × 10-6 for the dense 20 km s-1 Sgr A molecular cloud where our largest sources of uncertainties are Li I/Li, B I/B, and N(H). Our observations imply (Li/H)GC < 22 (Li/H)disk, (Li/H)GC < 39 (Li/H)disk-spallation, (B/H)GC < 1.2 × 104 (B/H)disk, (B/H)GC < 1.5 × 104 (B/H)disk-spallation. For a simple model combining mass loss from AGB stars (only for Li), spallation reactions, and SN ν-nucleosynthesis, we estimate (Li/H)GC = 1.3 × 10-8 (13 times enhancement) and (B/H)GC = 7.4 × 10-9 (10 times enhancement). If Li is primarily produced via spallation reactions from a cosmic-ray proton flux φp(t) with the same energy and trapping as in the disk, then [\\smallint φp(t)dt]GC < 13[\\smallint φp(t)dt]disk. Comparing our results to AGN models, we conclude that the GC has not had an extended period of AGN activity containing a large cosmic-ray flux (LCR <= 1044 ergs s-1 for 108 yr), a large low-energy cosmic-ray flux (less than 100 times the disk flux), or a large γ-ray flux (Lγ < 1042 ergs s-1 for 109 yr). Furthermore, since any Galactic deuterium production will significantly enhance the abundances of Li and B, our results imply that there are no sources of D in the GC or Galaxy. Therefore, all the Galactic D originated from the infall of primordial matter with the current D/H reduced by astration and mixing.

  14. Multiple populations in more metal-rich galactic globular clusters

    NASA Astrophysics Data System (ADS)

    Cordero, Maria J.

    In this thesis we present chemical abundances for bright stars in the intermediate metallicity globular cluster (GC) M5, and the relatively metal-rich GCs M71 and 47 Tuc with the goal of improving the understanding of chemical evolution in the metallicity regime sampled by these three GCs. The first chapter presents a brief historical overview in light element abundance variations in globular clusters. In the second chapter we present the results obtained for 47 Tuc, the most-metal rich cluster of my sample. 47 Tuc is an ideal target to study chemical evolution and GC formation in massive more metal-rich GCs since it is the closest massive GC. Chemical abundances for O, Na, Al, Si, Ca, Ti, Fe, Ni, La, and Eu were determined for 164 red giant branch (RGB) stars in 47 Tuc using spectra obtained with both the Hydra multi-fiber spectrograph at the Blanco 4-m telescope and the FLAMES multi-object spectrograph at the ESO Very Large Telescope. The average [Fe/H]= --0.79+/-0.09 dex is consistent with literature values, as well as over-abundances of alpha-elements ([alpha/Fe] ~ 0.3 dex). The n-capture process elements indicate that 47 Tuc is r-process dominated ([Eu/La]=+0.24), and the light elements O, Na, and Al exhibit star-to-star variations. The Na-O anti-correlation, a signature typically seen in Galactic GCs, is present in 47 Tuc, and extends to include a small number of stars with [O/Fe] ~ --0.5. Additionally, the [O/Na] ratios of our sample reveal that the cluster stars can be separated into three distinct populations. A KS-test demonstrates that the O-poor/Na-rich stars are more centrally concentrated than the O-rich/Na-poor stars. The observed number and radial distribution of 47 Tuc's stellar populations, as distinguished by their light element composition, agrees closely with the results obtained from photometric data. We do not find evidence supporting a strong Na-Al correlation in 47 Tuc, which is consistent with current models of AGB nucleosynthesis yields

  15. 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.

  16. 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.

  17. 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.

  18. 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).

  19. Fermi Galactic Center Zoom

    NASA Video Gallery

    This animation zooms into an image of the Milky Way, shown in visible light, and superimposes a gamma-ray map of the galactic center from NASA's Fermi. Raw data transitions to a view with all known...

  20. Galactic cosmic ray composition

    NASA Technical Reports Server (NTRS)

    Meyer, J. P.

    1986-01-01

    An assessment is given of the galactic cosmic ray source (GCRS) elemental composition and its correlation with first ionization potential. The isotopic composition of heavy nuclei; spallation cross sections; energy spectra of primary nuclei; electrons; positrons; local galactic reference abundances; comparison of solar energetic particles and solar coronal compositions; the hydrogen; lead; nitrogen; helium; and germanium deficiency problems; and the excess of elements are among the topics covered.

  1. 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.

  2. 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.

  3. 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).

  4. Carbon-enhanced metal-poor stars: a window on AGB nucleosynthesis and binary evolution. II. Statistical analysis of a sample of 67 CEMP-s stars

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    Many of the carbon-enhanced metal-poor (CEMP) stars that we observe in the Galactic halo are found in binary systems and show enhanced abundances of elements produced by the slow neutron-capture process (s-elements). The origin of the peculiar chemical abundances of these CEMP-s stars is believed to be accretion in the past of enriched material from a primary star in the asymptotic giant branch (AGB) phase of its evolution.We investigate the mechanism of mass transfer and the process of nucleosynthesis in low-metallicity AGB stars by modelling the binary systems in which the observed CEMP-s stars were formed.For this purpose we compare a sample of 67 CEMP-s stars with a grid of binary stars generated by our binary evolution and nucleosynthesis model. We classify our sample CEMP-s stars in three groups based on the observed abundance of europium. In CEMP-s/r stars the europium-to-iron ratio is more than ten times higher than in the Sun, whereas it is lower than this threshold in CEMP-s/nr stars. No measurement of europium is currently available for CEMP-s/ur stars.On average our models reproduce the abundances observed in CEMP-s/nr stars well, whereas in CEMP-s/r stars and CEMP-s/ur stars the abundances of the light-s elements (strontium, yttrium, zirconium) are systematically overpredicted by our models, and in CEMP-s/r stars the abundances of the heavy-s elements (barium, lanthanum) are underestimated. In all stars our modelled abundances of sodium overestimate the observations. This discrepancy is reduced only in models that underestimate the abundances of most of the s-elements. Furthermore, the abundance of lead is underpredicted in most of our model stars, independent of the metallicity. These results point to the limitations of our AGB nucleosynthesis model, particularly in the predictions of the element-to-element ratios. In our models CEMP-s stars are typically formed in wide systems with periods above 10 000 days, while most of the observed CEMP-s stars

  5. 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.

  6. VERITAS Galactic Observations

    NASA Astrophysics Data System (ADS)

    Hughes, Gareth

    2013-06-01

    We report on recent Galactic results and discoveries made by the VERITAS collaboration. The Very Energetic Radiation Imaging Telescope Array System (VERITAS) is a ground-based gamma-ray observatory, located in southern Arizona, able to detect gamma rays of energies from 100 GeV up to 30 TeV. VERITAS has been fully operational since 2007 and its current sensitivity enables the detection of a 1% Crab Nebula flux at 5 sigma in under 30 hours. The observatory is well placed to view large parts of the galactic plane including its center, resulting in a strong galactic program. Objects routinely observed include Pulsars, Pulsar Wind Nebula, X-ray binaries and sources with unidentified counterparts in other wavelengths.

  7. Spitzer Digs Up Galactic Fossil

    NASA Technical Reports Server (NTRS)

    2004-01-01

    [figure removed for brevity, see original site] Figure 1

    [figure removed for brevity, see original site] Figure 2

    This false-color image taken by NASA's Spitzer Space Telescope shows a globular cluster previously hidden in the dusty plane of our Milky Way galaxy. Globular clusters are compact bundles of old stars that date back to the birth of our galaxy, 13 or so billion years ago. Astronomers use these galactic 'fossils' as tools for studying the age and formation of the Milky Way.

    Most clusters orbit around the center of the galaxy well above its dust-enshrouded disc, or plane, while making brief, repeated passes through the plane that each last about a million years. Spitzer, with infrared eyes that can see into the dusty galactic plane, first spotted the newfound cluster during its current pass. A visible-light image (inset of Figure 1) shows only a dark patch of sky.

    The red streak behind the core of the cluster is a dust cloud, which may indicate the cluster's interaction with the Milky Way. Alternatively, this cloud may lie coincidentally along Spitzer's line of sight.

    Follow-up observations with the University of Wyoming Infrared Observatory helped set the distance of the new cluster at about 9,000 light-years from Earth - closer than most clusters - and set the mass at the equivalent of 300,000 Suns. The cluster's apparent size, as viewed from Earth, is comparable to a grain of rice held at arm's length. It is located in the constellation Aquila.

    Astronomers believe that this cluster may be one of the last in our galaxy to be uncovered.

    This image composite was taken on April 21, 2004, by Spitzer's infrared array camera. It is composed of images obtained at four wavelengths: 3.6 microns (blue), 4.5 microns (green), 5.8 microns (orange) and 8 microns (red).

    Galactic Fossil Found Behind Curtain of Dust In Figure 2, the image mosaic shows the same patch of sky in various wavelengths of light. While the

  8. 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.

  9. Iron and Nickel Isotopic Compositions of Presolar Silicon Carbide Grains from AGB Stars Measured with CHILI

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

    Simultaneous iron and nickel isotopic studies in presolar SiC mainstream grains measured on CHILI show the expected AGB star anomalies in the neutron-rich isotopes. Neutron-poor isotopes are dominated by GCE and show clear correlations with silicon.

  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. 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.

  12. Red supergiants as type II supernova progenitors

    NASA Astrophysics Data System (ADS)

    Negueruela, Ignacio; Dorda, Ricardo; González-Fernández, Carlos; Marco, Amparo

    2015-08-01

    Recent searches for supernova IIp progenitors in external galaxies have led to the identification of red objects with magnitudes and colours indicative of red supergiants, in most cases implying quite low luminosities and hence masses well below 10Msol. Stellar models, on the other hand, do not predict explosions from objects below 9 Msol. What does our knowledge of local red supergiants tells us about the expected properties of such objects?We have carried out a comprehensive spectroscopic and photometric study of a sample of hundreds of red supergiants in the Milky Way and both Magellanic Clouds. We have explored correlations between different parameters and the position of stars in the HR diagrams of open clusters. At solar metallicty, there is strong evidence for a phase of very heavy mass loss at the end of the red supergiant phase, but the existence of such a phase is still not confirmed at SMC metallicities. Objects of ~ 7Msol, on the other hand, become very dusty in the SMC, and appear as very luminous Miras.Among Milky Way clusters, we find a surprising lack of objects readily identifiable as the expected 7 to 10 Msol red supergiants or AGB stars. We are carrying out an open cluster survey aimed at filling this region of the HR diagram with reliable data. Finally, we will discuss the implications of all this findings for the expected properties of supernova progenitors, as it looks unlikely that typical red supergiants may explode without undergoing further evolution.

  13. 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.

  14. Production and Recycling of Carbon in the Early Galactic Halo

    NASA Astrophysics Data System (ADS)

    Andersen, Johannes; Thidemann Hansen, Terese; Nordström, Birgitta

    2015-08-01

    Extremely metal-poor (EMP) stars - [Fe/H] below ~ -3 - are fossil records of the conditions in the early halo. High-resolution 8m-class spectroscopy has shown that the detailed abundance pattern of EMP giant stars is surprisingly uniform and essentially Solar (e.g. Bonifacio+ 2012), apart from the usual α-enhancement in the halo. In the simplest picture, iron is a proxy for both overall metallicity and time, so the EMP stars should form before the oldest and most metal-poor Galactic globular clusters, notably at the lowest metallicities ([Fe/H] ≲ -3.5).It is thus striking that 20-40% of the EMP giants are strongly enhanced in carbon - the CEMP stars (Lucatello+ 2006). This is conventionally ascribed to mass transfer from a former AGB binary companion, and from a limited compilation of data, Lucatello+ (2005) concluded that most or all CEMP stars are indeed binaries, similar to the classical Ba and CH stars (e.g. Jorissen+ 1998). However, most of the sample was of the inner-halo CEMP-s variety (C and s-process elements both enhanced), while CEMP-no stars dominate the outer halo (Carollo+ 2014). Our precise radial velocity monitoring for CEMP stars over 8 years shed light on this issue.Our data suggest a normal binary frequency for the CEMP-no stars; i.e. the C was not produced in a binary companion, but in sites at interstellar distances, e.g. ‘faint’ SNe, and imprinted on the natal clouds of the low-mass stars we observe. This has immediate implications for the formation of dust in primitive, high-redshift galaxies (Watson+ 2015) and the origin of C-enhanced DLAs (Cooke+ 2011, 2012). The CEMP-s binary orbits are also revealing, with periods up to several decades and generally low amplitudes and eccentricities, suggesting that EMP AGB stars have very large radii, facilitating extensive mass loss. More work on faint SNe and EMP AGB envelopes is needed!

  15. 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

  16. The Hubble Space TelescopeUV Legacy Survey of Galactic Globular Clusters - V. Constraints on formation scenarios

    NASA Astrophysics Data System (ADS)

    Renzini, A.; D'Antona, F.; Cassisi, S.; King, I. R.; Milone, A. P.; Ventura, P.; Anderson, J.; Bedin, L. R.; Bellini, A.; Brown, T. M.; Piotto, G.; van der Marel, R. P.; Barbuy, B.; Dalessandro, E.; Hidalgo, S.; Marino, A. F.; Ortolani, S.; Salaris, M.; Sarajedini, A.

    2015-12-01

    We build on the evidence provided by our Legacy Survey of Galactic globular clusters (GC) to submit to a crucial test four scenarios currently entertained for the formation of multiple stellar generations in GCs. The observational constraints on multiple generations to be fulfilled are manifold, including GC specificity, ubiquity, variety, predominance, discreteness, supernova avoidance, p-capture processing, helium enrichment and mass budget. We argue that scenarios appealing to supermassive stars, fast rotating massive stars and massive interactive binaries violate in an irreparable fashion two or more among such constraints. Also the scenario appealing to asymptotic giant branch (AGB) stars as producers of the material for next generation stars encounters severe difficulties, specifically concerning the mass budget problem and the detailed chemical composition of second-generation stars. We qualitatively explore ways possibly allowing one to save the AGB scenario, specifically appealing to a possible revision of the cross-section of a critical reaction rate destroying sodium, or alternatively by a more extensive exploration of the vast parameter space controlling the evolutionary behaviour of AGB stellar models. Still, we cannot ensure success for these efforts and totally new scenarios may have to be invented to understand how GCs formed in the early Universe.

  17. Study of galactic light, extragalactic light, and galactic structure using pioneer 10 observations of background starlight

    SciTech Connect

    Toller, G.N.

    1981-01-01

    An observational and theoretical study of the diffuse astronomical background sky brightness (background starlight) is carried out. The brightness is determined over 95% of the sky using Pioneer 10 photometric measurements in sky regions where the zodiacal light is negligible (heliocentric distances approx. greater than or equal to 3. A.U.). Brightness levels are presented at blue (3950 to 4850 A) and red (5900 to 6800 A) wavelengths. The B-R color index distribution is established over the celestial sphere. Pioneer 10 results are compared with previous star count and ground based photometric studies to separate background starlight into its constituent parts: integrated starlight, diffuse galactic light (DGL), and cosmic light. Significant errors are found in published star count results at low galactic latitudes. The galactic latitude (b'') and longitude (1'') dependences of integrated starlight and the variation of DGL with b'' are determined. An upper limit of 3.9 S/sub 10/(V)/sub G2V/ at the 90% confidence level is deduced for the cosmic light brightness at blue wavelengths near the galactic poles. The integrated light from discrete galaxies adequately explains this component of the background starlight.

  18. Short-lived Isotopes from a Close-by AGB Star Triggering the Protosolar Nebula

    NASA Astrophysics Data System (ADS)

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

    The presence of short-lived isotopes in the early solar system, in particular 26Al, 41Ca, 60Fe, and 107Pd, point to a close-by and fresh nucleosynthesis source, possibly triggering the collapse of the protosolar nebula. We present the results of nucleosynthesis calculations based on an AGB polluting hypothesis. A general concordance of the predicted yields of the above radioactivities relative to 26Al can be obtained in the case of an intermediate mass AGB star with hot bottom burning in the envelope (thus producing 26Al), and mixing through a series of third dredge-up episodes a fraction of the C-rich and s-processed material from the He intershell with the extended envelope. Polution of the protosolar nebula with freshly synthesized material may derive from the efficient winds of the AGB star. In AGB stars, the s-process nucleosynthesis occurs both during the maximum phase of every thermal runaway, driven by the partial activation of the 22Ne(alpha,n)25Mg reaction, and in the interpulse phase, where the 13C nuclei are fully consumed in radiative conditions by the activation of the 13C(alpha,n)16O reaction. We have used different prescriptions for the amount of the 13C nuclei present in the intershell. A minimum amount of 13C is naturally expected in the ashes of H-shell burning. Possible formation of an extra "13C-pocket" derives from the injection of a small amount of protons from the envelope into the 12C-rich intershell during any third dredge-up episode, when the H-shell is inactivated. Prediction for other short-lived, 36Cl, 135Cs, and 205Pb, are given. General consequences for the pollution of the protosolar nebula with newly synthesized stable isotopes from the AGB winds are outlined. The origin of other detected short-lived nuclei, in particular 53Mn, 129I, and 182Hf, which cannot come from an AGB source, is analysed. The alternative trigger hypothesis by a close-by Supernova is discussed.

  19. 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.

  20. Galactic-scale civilization

    NASA Technical Reports Server (NTRS)

    Kuiper, T. B. H.

    1980-01-01

    Evolutionary arguments are presented in favor of the existence of civilization on a galactic scale. Patterns of physical, chemical, biological, social and cultural evolution leading to increasing levels of complexity are pointed out and explained thermodynamically in terms of the maximization of free energy dissipation in the environment of the organized system. The possibility of the evolution of a global and then a galactic human civilization is considered, and probabilities that the galaxy is presently in its colonization state and that life could have evolved to its present state on earth are discussed. Fermi's paradox of the absence of extraterrestrials in light of the probability of their existence is noted, and a variety of possible explanations is indicated. Finally, it is argued that although mankind may be the first occurrence of intelligence in the galaxy, it is unjustified to presume that this is so.

  1. The Galactic Bulge

    NASA Astrophysics Data System (ADS)

    Barbuy, B.

    2016-06-01

    The Galactic bulge is the least studied component of our Galaxy. Yet, its formation and evolution are key to understand the formation of the Galaxy itself. Studies on the Galactic bulge have increased significantly in the last years, but still there are many points of controversy. This volume contains several contributions from experts in different aspects of the bulge. Issues discussed include the following: the presence of an old spheroidal bulge, or identification of its old stellar population with the thick disk or halo; fraction of stars younger than 10 Gyr is estimated to be of < 5 to 22% depending on method and authors; multiple populations or only a metal-poor and a metal-rich ones; spheroidal or ellipsoidal distribution of RR Lyrae; formation of the bulge from early mergers or from secular evolution of the bar; different methods of mapping extinction; selection and identification of bulge globular clusters.

  2. Grains in galactic haloes.

    NASA Astrophysics Data System (ADS)

    Ferrara, A.; Barsella, B.; Ferrini, F.; Greenberg, J. M.; Aiello, S.

    1989-12-01

    The authors considered the effect of extensive forces on dust grains subjected to the light and matter distribution of the spiral galaxy NGC 3198. They have shown that the combined force on a small particle located above the plane of a galactic disk may be either attractive or repulsive depending on a variety of parameters. The authors present here the preliminary results of the study of the motion of a dust grain for NGC 3198.

  3. Galactic oscillator symmetry

    NASA Technical Reports Server (NTRS)

    Rosensteel, George

    1995-01-01

    Riemann ellipsoids model rotating galaxies when the galactic velocity field is a linear function of the Cartesian coordinates of the galactic masses. In nuclear physics, the kinetic energy in the linear velocity field approximation is known as the collective kinetic energy. But, the linear approximation neglects intrinsic degrees of freedom associated with nonlinear velocity fields. To remove this limitation, the theory of symplectic dynamical symmetry is developed for classical systems. A classical phase space for a self-gravitating symplectic system is a co-adjoint orbit of the noncompact group SP(3,R). The degenerate co-adjoint orbit is the 12 dimensional homogeneous space Sp(3,R)/U(3), where the maximal compact subgroup U(3) is the symmetry group of the harmonic oscillator. The Hamiltonian equations of motion on each orbit form a Lax system X = (X,F), where X and F are elements of the symplectic Lie algebra. The elements of the matrix X are the generators of the symplectic Lie algebra, viz., the one-body collective quadratic functions of the positions and momenta of the galactic masses. The matrix F is composed from the self-gravitating potential energy, the angular velocity, and the hydostatic pressure. Solutions to the hamiltonian dynamical system on Sp(3,R)/U(3) are given by symplectic isospectral deformations. The Casimirs of Sp(3,R), equal to the traces of powers of X, are conserved quantities.

  4. Galactic Diffuse Emissions

    SciTech Connect

    Digel, Seth W.; /SLAC

    2007-10-25

    Interactions of cosmic rays with interstellar nucleons and photons make the Milky Way a bright, diffuse source of high-energy {gamma}-rays. Observationally, the results from EGRET, COMPTEL, and OSSE have now been extended to higher energies by ground-based experiments, with detections of diffuse emission in the Galactic center reported by H.E.S.S. in the range above 100 GeV and of diffuse emission in Cygnus by MILAGRO in the TeV range. In the range above 100 keV, INTEGRAL SPI has found that diffuse emission remains after point sources are accounted for. I will summarize current knowledge of diffuse {gamma}-ray emission from the Milky Way and review some open issues related to the diffuse emission -- some old, like the distribution of cosmic-ray sources and the origin of the 'excess' of GeV emission observed by EGRET, and some recently recognized, like the amount and distribution of molecular hydrogen not traced by CO emission -- and anticipate some of the advances that will be possible with the Large Area Telescope on GLAST. We plan to develop an accurate physical model for the diffuse emission, which will be useful for detecting and accurately characterizing emission from Galactic point sources as well as any Galactic diffuse emission from exotic processes, and for studying the unresolved extragalactic emission.

  5. Galactic diffuse gamma rays from galactic plane

    NASA Astrophysics Data System (ADS)

    Tateyama, N.; Nishimura, J.

    2001-08-01

    The dominant part of the diffuse gamma rays from the Galactic plane, with energy greater than 1TeV, has been thought as due to the inverse Compton scattering of the interstellar photons with the high-energy cosmic electrons. In these energy regions, the diffuse gamma-ray observation gives us unique infor-mation on the energy spectrum of the high-energy electrons in the interstellar space, since we cannot observe those electrons directly. This provides us information on the cosmicray source, production mechanism and propagation in the Galaxy. We discuss the implication of our results by comparing with the work of Porter and Protheroe, and also compare with the data observed by the most recent extensive air showers. It is also pointed out that the patchy structure of gammaray distribution will appear at high-energy side, if we observe the distribution with a higher angular resolution of a few arc degrees. This patchy structure will become clear beyond 10TeV of IC gamma rays, where the number of contributing sources of parent decrease and the diffusion distance of the electrons become smaller.

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  7. 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.

  8. The Nearby AGB Star L2 Puppis: The Birth Of a Planetary Nebula?

    NASA Astrophysics Data System (ADS)

    Kervella, P.; Montargès, M.; Lagadec, E.

    2015-12-01

    Adaptive optics observations in the infrared (VLT/NACO, Kervella et al. [6]) and visible (VLT/SPHERE, Kervella et al. [7]) domains revealed that the nearby AGB star L2 Pup (d = 64 pc) is surrounded by a dust disk seen almost edge-on. Thermal emission from a large dust "loop" is detected at 4 μm up to more than 10 AU from the star. We also detect a secondary source at a separation of 32 mas, whose nature is uncertain. L2 Pup is currently a relatively "young" AGB star, so we may witness the formation of a planetary nebula. The mechanism that breaks the spherical symmetry of mass loss is currently uncertain, but we propose that the dust disk and companion are key elements in the shaping of the bipolar structure. L2 Pup emerges as an important system to test this hypothesis.

  9. 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.

  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. 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.

  12. 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.

  13. 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.

  14. Winds of M-type AGB stars driven by micron-sized grains

    NASA Astrophysics Data System (ADS)

    Höfner, S.

    2008-11-01

    Context: In view of the recent problem regarding the dynamical modelling of winds of M-type AGB stars (insufficient radiation pressure on silicate grains), some of the basic assumptions of these models need to be re-evaluated critically. Aims: Accepting the conclusion that non-grey effects will force silicate grains to be virtually Fe-free, the viability of driving winds with micron-sized Fe-free silicates, instead of small particles, is examined. Methods: Using both simple estimates and detailed dynamical atmosphere and wind models, it is demonstrated that radiation pressure on Fe-free silicate grains is sufficient to drive outflows if the restriction to the small particle limit is relaxed, and prevailing thermodynamic conditions allow grains to grow to sizes in the micrometer range. Results: The predicted wind properties, such as mass loss rates and outflow velocities, are in good agreement with observations of M-type AGB stars. Due to a self-regulating feedback between dust condensation and wind acceleration, grain growth naturally comes to a halt at particle diameters of about 1~μm. Conclusions: The most efficient grain sizes to drive winds are in a rather narrow interval around 1~μm. These values are set by the wavelength range corresponding to the flux maximum in typical AGB stars, and are very similar to interstellar grains.

  15. The lead discrepancy in intrinsically s-process enriched post-AGB stars in the Magellanic Clouds

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    Context. Our understanding of the s-process nucleosynthesis in asymptotic giant branch (AGB) stars is incomplete. AGB models predict, for example, large overabundances of lead (Pb) compared to other s-process elements in metal-poor low-mass AGB stars. This is indeed observed in some extrinsically enhanced metal-poor stars, but not in all. An extensive study of intrinsically s-process enriched objects is essential for improving our knowledge of the AGB third dredge-up and associated s-process nucleosynthesis. Aims: We compare the spectral abundance analysis of the SMC post-AGB star J004441.04-732136.4 with state-of-the-art AGB model predictions with a main focus on Pb. The low signal-to-noise (S/N) in the Pb line region made the result of our previous study inconclusive. We acquired additional data covering the region of the strongest Pb line. Methods: By carefully complementing re-reduced previous data, with newly acquired UVES optical spectra, we improve the S/N of the spectrum around the strongest Pb line. Therefore, an upper limit for the Pb abundance is estimated from a merged weighted mean spectrum using synthetic spectral modeling. We then compare the abundance results from the combined spectra to predictions of tailored AGB evolutionary models from two independent evolution codes. In addition, we determine upper limits for Pb abundances for three previously studied LMC post-AGB objects. Results: Although theoretical predictions for J004441.04-732136.4 match the s-process distribution up to tungsten (W), the predicted very high Pb abundance is clearly not detected. The three additional LMC post-AGB stars show a similar lack of a very high Pb abundance. Conclusions: From our study, we conclude that none of these low-mass, low-metallicity post-AGB stars of the LMC and SMC are strong Pb producers. This conflicts with current theoretical predictions. Based on observations collected with the Very Large Telescope at the ESO Paranal Observatory (Chili) of programme

  16. 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

  17. 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

  18. Full spectrum of turbulence convective mixing. II. Lithium production in AGB stars

    NASA Astrophysics Data System (ADS)

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

    1999-08-01

    We present results from new, detailed computations of lithium production by hot bottom burning (HBB) in asymptotic giant branch (AGB) stars of intermediate mass (3.5 <= M <= 6 M_sun). The dependence of lithium production on stellar mass, metallicity, mass loss rate, convection and overshooting are discussed. In particular, nuclear burning, turbulent mixing and convective overshooting (if any) are self-consistently coupled by a diffusive algorithm, and the Full Spectrum of Turbulence (FST) model of convection is adopted, with test comparisons to Mixing Length Theory (MLT) stellar models. All the evolutions are followed from pre-main sequence down to late AGB, when stars do not appear any longer lithium rich. A ``reference mass" of 6 M_sun has been chosen since, although relatively close to the upper limit for which degenerate (12) C ignition occurs, all the studied mechanisms show up more clearly. HBB is always found above ~ log L/L_sun = 4.4, but the range of (initial) masses reaching HBB is largely dependent on convection model, overshooting and metallicity. For solar chemistry, masses >= 4M_sun evolve through HBB in the FST case and including core overshooting whereas, with solarly tuned MLT models and no overshooting, only masses >= 6M_sun can reach HBB. These constraints can give feedbacks about the more correct convection model and/or the extent of overshooting, thanks to the signatures of HBB in AGB stars in clusters of known turnoff masses and metallicity. Overshooting (when included) is addressed as an exponentially decreasing diffusion above formally convective regions. It makes convective cores during the main sequence to grow larger, and also starting masses and luminosities in AGB are then larger. However, also preliminary results obtained when allowing displacement of convective elements below convective regions in AGB are shown. In the ``reference" case (6M_sun), we find that overshooting from below the convective envelope totally suppresses thermal

  19. 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

  20. Red Sea

    Atmospheric Science Data Center

    2013-04-16

    article title:  The Red Sea     View Larger Image ... Imaging SpectroRadiometer (MISR) image of the Red Sea was acquired on August 13, 2000. Located between the East African coast and the Saudi Arabian peninsula, the Red Sea got its name because the blooms of a type of algae,  Trichodesmium ...

  1. The Inner Galactic Bulge: Evidence for a Nuclear Bar?

    NASA Astrophysics Data System (ADS)

    Gerhard, Ortwin; Martinez-Valpuesta, Inma

    2012-01-01

    Recent data from the VVV survey have strengthened evidence for a structural change in the Galactic bulge inward of |l| <= 4°. Here we show with an N-body barred galaxy simulation that a boxy bulge formed through the bar and buckling instabilities effortlessly matches measured bulge longitude profiles for red clump stars. The same simulation snapshot was earlier used to clarify the apparent boxy bulge—long bar dichotomy, for the same orientation and scaling. The change in the slope of the model longitude profiles in the inner few degrees is caused by a transition from highly elongated to more nearly axisymmetric isodensity contours in the inner boxy bulge. This transition is confined to a few degrees from the Galactic plane; thus the change of slope is predicted to disappear at higher Galactic latitudes. We also show that the nuclear star count map derived from this simulation snapshot displays a longitudinal asymmetry similar to that observed in the Two Micron All Sky Survey (2MASS) data, but is less flattened to the Galactic plane than the 2MASS map. These results support the interpretation that the Galactic bulge originated from disk evolution and question the evidence advanced from star count data for the existence of a secondary nuclear bar in the Milky Way.

  2. THE INNER GALACTIC BULGE: EVIDENCE FOR A NUCLEAR BAR?

    SciTech Connect

    Gerhard, Ortwin; Martinez-Valpuesta, Inma

    2012-01-15

    Recent data from the VVV survey have strengthened evidence for a structural change in the Galactic bulge inward of |l| {<=} 4 Degree-Sign . Here we show with an N-body barred galaxy simulation that a boxy bulge formed through the bar and buckling instabilities effortlessly matches measured bulge longitude profiles for red clump stars. The same simulation snapshot was earlier used to clarify the apparent boxy bulge-long bar dichotomy, for the same orientation and scaling. The change in the slope of the model longitude profiles in the inner few degrees is caused by a transition from highly elongated to more nearly axisymmetric isodensity contours in the inner boxy bulge. This transition is confined to a few degrees from the Galactic plane; thus the change of slope is predicted to disappear at higher Galactic latitudes. We also show that the nuclear star count map derived from this simulation snapshot displays a longitudinal asymmetry similar to that observed in the Two Micron All Sky Survey (2MASS) data, but is less flattened to the Galactic plane than the 2MASS map. These results support the interpretation that the Galactic bulge originated from disk evolution and question the evidence advanced from star count data for the existence of a secondary nuclear bar in the Milky Way.

  3. THE GALACTIC MAGNETIC FIELD

    SciTech Connect

    Jansson, Ronnie; Farrar, Glennys R.

    2012-12-10

    With this Letter, we complete our model of the Galactic magnetic field (GMF), by using the WMAP7 22 GHz total synchrotron intensity map and our earlier results to obtain a 13-parameter model of the Galactic random field, and to determine the strength of the striated random field. In combination with our 22-parameter description of the regular GMF, we obtain a very good fit to more than 40,000 extragalactic Faraday rotation measures and the WMAP7 22 GHz polarized and total intensity synchrotron emission maps. The data call for a striated component to the random field whose orientation is aligned with the regular field, having zero mean and rms strength Almost-Equal-To 20% larger than the regular field. A noteworthy feature of the new model is that the regular field has a significant out-of-plane component, which had not been considered earlier. The new GMF model gives a much better description of the totality of data than previous models in the literature.

  4. Testing Galactic Cosmic Ray Models

    NASA Technical Reports Server (NTRS)

    Adams, James H., Jr.

    2009-01-01

    Models of the Galactic Cosmic Ray Environment are used for designing and planning space missions. The existing models will be reviewed. Spectral representations from these models will be compared with measurements of galactic cosmic ray spectra made on balloon flights and satellite flights over a period of more than 50 years.

  5. Testing Galactic Cosmic Ray Models

    NASA Technical Reports Server (NTRS)

    Adams, James H., Jr.

    2010-01-01

    Models of the Galactic Cosmic Ray Environment are used for designing and planning space missions. The exising models will be reviewed. Spectral representations from these models will be compared with measurements of galactic cosmic ray spectra made on balloon flights and satellite flights over a period of more than 50 years.

  6. Galactic cosmic rays and nucleosynthesis

    SciTech Connect

    Kiener, Juergen

    2010-03-01

    The nucleosynthesis of the light elements Li, Be and B by galactic cosmic rays is presented. Observations of cosmic rays and the nuclear reactions responsible for Li, Be and B nucleosynthesis are described, followed by some words on propagation. At the end, some open questions concerning galactic cosmic rays are discussed.

  7. Distribution of SiO and OH Maser Stars in the Galactic Plane

    NASA Astrophysics Data System (ADS)

    Jiang, Bi-Wei; Jia, Shu-Mei

    2001-04-01

    The observational results of the Nobeyama 45-m SiO maser survey and the Arecibo 305-m OH maser survey are assembled for an analysis of the distribution and kinematics of late-type stars in the Galactic plane. It is found that neither SiO maser stars nor OH maser stars show any concentration to the spiral arms, which imply that they do not belong to the arm population and quite possibly they are low-mass stars in late stage of evolution. A rotational curve is also derived for these objects and a few features which may be real are discussed and compared with those derived from planetary nebulae and AGB stars.

  8. Galactic Hearts of Glass

    NASA Technical Reports Server (NTRS)

    2006-01-01

    [figure removed for brevity, see original site] Click on image for larger graph

    This artist's concept shows delicate greenish crystals sprinkled throughout the violent core of a pair of colliding galaxies. The white spots represent a thriving population of stars of all sizes and ages. NASA's Spitzer Space Telescope detected more than 20 bright and dusty galactic mergers like the one depicted here, all teeming with the tiny gem-like crystals.

    When galaxies collide, they trigger the birth of large numbers of massive stars. Astronomers believe these blazing hot stars act like furnaces to produce silicate crystals in the same way that glass is made from sand. The stars probably shed the crystals as they age, and as they blow apart in supernovae explosions.

    At the same time the crystals are being churned out, they are also being destroyed. Fast-moving particles from supernova blasts easily convert silicates crystals back to their amorphous, or shapeless, form.

    How is Spitzer seeing the crystals if they are rapidly disappearing? Astronomers say that, for a short period of time at the beginning of galactic mergers, massive stars might be producing silicate crystals faster than they are eliminating them. When our own galaxy merges with the Andromeda galaxy in a few billion years, a similar burst of massive stars and silicate crystals might occur.

    Crystal Storm in Distant Galaxy The graph (see inset above) of infrared data from NASA's Spitzer Space Telescope tells astronomers that a distant galaxy called IRAS 08752+3915 is experiencing a storm of tiny crystals made up of silicates. The crystals are similar to the glass-like grains of sand found on Earth's many beaches.

    The data were taken by Spitzer's infrared spectrograph, which splits light open to reveal its rainbow-like components. The resulting spectrum shown here reveals the signatures of both crystalline (green) and non-crystalline (brown) silicates.

    Spitzer detected the same

  9. STELLAR TRANSITS IN ACTIVE GALACTIC NUCLEI

    SciTech Connect

    Beky, Bence; Kocsis, Bence E-mail: bkocsis@cfa.harvard.edu

    2013-01-01

    Supermassive black holes (SMBHs) are typically surrounded by a dense stellar population in galactic nuclei. Stars crossing the line of site in active galactic nuclei (AGNs) produce a characteristic transit light curve, just like extrasolar planets do when they transit their host star. We examine the possibility of finding such AGN transits in deep optical, UV, and X-ray surveys. We calculate transit light curves using the Novikov-Thorne thin accretion disk model, including general relativistic effects. Based on the expected properties of stellar cusps, we find that around 10{sup 6} solar mass SMBHs, transits of red giants are most common for stars on close orbits with transit durations of a few weeks and orbital periods of a few years. We find that detecting AGN transits requires repeated observations of thousands of low-mass AGNs to 1% photometric accuracy in optical, or {approx}10% in UV bands or soft X-ray. It may be possible to identify stellar transits in the Pan-STARRS and LSST optical and the eROSITA X-ray surveys. Such observations could be used to constrain black hole mass, spin, inclination, and accretion rate. Transit rates and durations could give valuable information on the circumnuclear stellar clusters as well. Transit light curves could be used to image accretion disks with unprecedented resolution, allowing us to resolve the SMBH silhouette in distant AGNs.

  10. Stellar Transits in Active Galactic Nuclei

    NASA Astrophysics Data System (ADS)

    Béky, Bence; Kocsis, Bence

    2013-01-01

    Supermassive black holes (SMBHs) are typically surrounded by a dense stellar population in galactic nuclei. Stars crossing the line of site in active galactic nuclei (AGNs) produce a characteristic transit light curve, just like extrasolar planets do when they transit their host star. We examine the possibility of finding such AGN transits in deep optical, UV, and X-ray surveys. We calculate transit light curves using the Novikov-Thorne thin accretion disk model, including general relativistic effects. Based on the expected properties of stellar cusps, we find that around 106 solar mass SMBHs, transits of red giants are most common for stars on close orbits with transit durations of a few weeks and orbital periods of a few years. We find that detecting AGN transits requires repeated observations of thousands of low-mass AGNs to 1% photometric accuracy in optical, or ~10% in UV bands or soft X-ray. It may be possible to identify stellar transits in the Pan-STARRS and LSST optical and the eROSITA X-ray surveys. Such observations could be used to constrain black hole mass, spin, inclination, and accretion rate. Transit rates and durations could give valuable information on the circumnuclear stellar clusters as well. Transit light curves could be used to image accretion disks with unprecedented resolution, allowing us to resolve the SMBH silhouette in distant AGNs.

  11. Grains in galactic haloes

    NASA Technical Reports Server (NTRS)

    Ferrara, Andrea; Barsella, Bruno; Ferrini, F.; Greenberg, J. Mayo; Aiello, Santi

    1989-01-01

    Researchers considered the effect of extensive forces on dust grains subjected to the light and matter distribution of a spiral galaxy (Greenberg et al. (1987), Ferrini et al. (1987), Barsella et al (1988). Researchers showed that the combined force on a small particle located above the plane of a galactic disk may be either attractive or repulsive depending on a variety of parameters. They found, for example, that graphite grains from 20 nm to 250 nm radius are expelled from a typical galaxy, while silicates and other forms of dielectrics, after initial expulsion, may settle in potential minimum within the halo. They discuss only the statistical behavior of the forces for 17 galaxies whose luminosity and matter distribution in the disk, bulge and halo components are reasonably well known. The preliminary results of the study of the motion of a dust grain for NGC 3198 are given.

  12. The Galactic Center

    NASA Astrophysics Data System (ADS)

    Genzel, Reinhard; Karas, Vladimír

    2007-04-01

    In the past decade high resolution measurements in the infrared employing adaptive optics imaging on 10m telescopes have allowed determining the three dimensional orbits stars within ten light hours of the compact radio source SgrA* at the Center of the Milky Way. These observations show that SgrA* is a three million solar mass black hole, beyond any reasonable doubt. The Galactic Center thus constitutes the best astrophysical evidence for the existence of black holes which have long been postulated, and is also an ideal 'lab' for studying the physics in the vicinity of such an object. Remarkably, young massive stars are present there and probably have formed in the innermost stellar cusp. Variable infrared and X-ray emission from SgrA* are a new probe of the physics and space time just outside the event horizon.

  13. Galactic Diffuse Polarized Emission

    NASA Astrophysics Data System (ADS)

    Carretti, Ettore

    2011-12-01

    Diffuse polarized emission by synchrotron is a key tool to investigate magnetic fields in the Milky Way, particularly the ordered component of the large scale structure. Key observables are the synchrotron emission itself and the RM is by Faraday rotation. In this paper the main properties of the radio polarized diffuse emission and its use to investigate magnetic fields will be reviewed along with our current understanding of the galactic magnetic field and the data sets available. We will then focus on the future perspective discussing RM-synthesis - the new powerful instrument devised to unlock the information encoded in such an emission - and the surveys currently in progress like S-PASS and GMIMS.

  14. Galactic Archaeology with the Subaru Prime Focus Spectrograph

    NASA Astrophysics Data System (ADS)

    Chiba, Masashi; Cohen, Judith; Wyse, Rosemary

    2015-08-01

    We present our Galactic Archaeology survey plan with the Prime Focus Spectrograph (PFS) for Subaru. PFS is a massively-multiplexed, fiber-fed optical and near-infrared 3-arm spectrograph (N_fiber = 2,400, 380 < lambda < 1260 nm, 1.3 degree diameter hexagonal field, low- and medium-resolution modes of R = 2,000-3,000 and 5,000, respectively), offering us unique opportunities in survey astronomy. Following successful design reviews, the instrument is now under construction with first light anticipated in 2018. In the Galactic Archaeology program, for which we expect to have about 100 nights over 5 years, radial velocities and chemical abundances of stars in the Milky Way and M31 will be used to infer the past assembly histories of these galaxies and the structure of their dark matter halos. Data will be secured for numerous stars in the Galactic thick-disk, halo and tidal streams as faint as V = 22 mag, including stars with V < 20 mag to complement the goals of the Gaia mission. A medium-resolution mode with R = 5,000 to be implemented in the red arm will allow the measurement of multiple alpha-element abundances and more precise velocities for Galactic stars, elucidating the detailed chemo-dynamical structure and evolution of each of the main stellar components of the Milky Way Galaxy and of its dwarf spheroidal galaxies. The M31 campaign will target red giant branch stars with 21.5 < V < 22.5 mag, obtaining radial velocities and metallicities over an unprecedented large area of its stellar halo. In synergy with these planned PFS survey, the coordinated imaging surveys with Hyper Suprime Cam are going on over wide areas of the Galactic satellites and the M31 halo, based on the combination of broad-band and narrow-band filters to separate candidate giants from foreground dwarfs as spectroscopic targets.

  15. Galactic plane gamma-radiation

    NASA Technical Reports Server (NTRS)

    Hartman, R. C.; Kniffen, D. A.; Thompson, D. J.; Fichtel, C. E.; Ogelman, H. B.; Tumer, T.; Ozel, M. E.

    1979-01-01

    Analysis of the SAS 2 data together with the COS B results shows that the distribution of galactic gamma-radiation has several similarities to that of other large-scale tracers of galactic structure. The radiation is primarily confined to a thin disc which exhibits offsets from b = 0 degrees similar to warping at radio frequencies. The principal distinction of the gamma-radiation is a stronger contrast in intensity between the region from 310 to 45 degrees in longitude and the regions away from the center that can be attributed to a variation in cosmic-ray density as a function of position in Galaxy. The diffuse galactic gamma-ray energy spectrum shows no significant variation in direction, and the spectrum seen along the plane is the same as that for the galactic component of the gamma-radiation at high altitudes. The uniformity of the galactic gamma-ray spectrum, the smooth decrease in intensity as a function of altitude, and the absence of any galactic gamma-ray sources at high altitudes indicate a diffuse origin for bulk of the galactic gamma-radiation rather than a collection of localized sources.

  16. Mapping the 12CO J = 1-0 and J = 2-1 emission in AGB and early post-AGB circumstellar envelopes. I. The COSAS program, first sample

    NASA Astrophysics Data System (ADS)

    Castro-Carrizo, A.; Quintana-Lacaci, G.; Neri, R.; Bujarrabal, V.; Schöier, F. L.; Winters, J. M.; Olofsson, H.; Lindqvist, M.; Alcolea, J.; Lucas, R.; Grewing, M.

    2010-11-01

    We present COSAS (CO Survey of late AGB Stars), a project to map and analyze the 12CO J = 1-0 and J = 2-1 line emission in a representative sample of circumstellar envelopes around AGB and post-AGB stars. The survey was undertaken with the aim of investigating small- and large-scale morphological and kinematical properties of the molecular environment surrounding stars in the late AGB and early post-AGB phases. For this, COSAS combines the high sensitivity and spatial resolving power of the IRAM Plateau de Bure interferometer with the better capability of the IRAM 30 m telescope to map extended emission. The global sample encompasses 45 stars selected to span a range in chemical type, variability type, evolutionary state, and initial mass. COSAS provides means to quantify variations in the mass-loss rates, assess morphological and kinematical features, and to investigate the appearance of fast aspherical winds in the early post-AGB phase. This paper, which is the first of a series of COSAS papers, presents the results from the analyses of a first sample of 16 selected sources. The envelopes around late AGB stars are found to be mostly spherical, often mingled with features such as concentric arcs (R Cas and TX Cam), a broken spiral density pattern (TX Cam), molecular patches testifying to aspherical mass-loss (WX Psc, IK Tau, V Cyg, and S Cep), and also with well-defined axisymmetric morphologies and kinematical patterns (X Her and RX Boo). The sources span a wide range of angular sizes, from relatively compact (CRL 2362, OH 104.9+2.4 and CRL 2477) to very large (χ Cyg and TX Cam) envelopes, sometimes partially obscured by self-absorption features, which particularly for IK Tau and χ Cyg testifies to the emergence of aspherical winds in the innermost circumstellar regions. Strong axial structures with more or less complex morphologies are detected in four early post-AGB stars (IRAS 20028+3910, IRAS 23321+6545, IRAS 19475+3119 and IRAS 21282+5050) of the sub

  17. 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

  18. 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.

  19. The excitation of circumstellar C2 in carbon-rich post-AGB object IRAS 22272+5435

    NASA Astrophysics Data System (ADS)

    Schmidt, M. R.; Začs, L.; Pułecka, M.; Szczerba, R.

    2013-08-01

    Context. Observations of the circumstellar envelopes of post-asymptotic giant branch (post-AGB) stars provide information about their mass-loss history during the AGB phase and about the chemistry inside envelopes after that phase. Aims: We analyze visual observations of C2 molecule in absorption and millimeter and sub-millimeter observations of CO molecule in emission with the aim of determining the physical and chemical conditions in the circumstellar shell of the carbon-rich post-AGB star IRAS 22272+5435. Methods: We determined the column densities and excitation structure of C2 from equivalent width analysis of the molecular absorptions. The thermal and density structure of post-AGB shell (AGB remnant) is constrained by multilevel radiative transfer modeling of CO emission lines. The chemical structure of the envelope was computed and then used in the multilevel radiative transfer in C2 for comparison with observed column densities. Results: We estimate the column density of C2 to be 3.2 × 1015 cm-2. From the chemical model we estimate peak abundance of C2 as 6.8 × 10-6 relative to nucleon density. The absorption of molecular lines originate in the ring between 5 and 10 × 1016 cm. The excitation temperature of the lowest levels of 58 K is consistent with the gas kinetic temperature derived from the CO modeling. The initial abundance of the parent molecule C2H2 inferred from the analysis is found to be 1.27 × 10-5 relative to nucleon density. Conclusions: C2 molecule is a promising tool for probing the temperature structure of the envelopes of post-AGB objects and indirectly for determining the chemical abundance of acetylene. Table 1 is available in electronic form at http://www.aanda.org

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. Spiral Galactic Formation and Evolution

    NASA Astrophysics Data System (ADS)

    Brekke, Stewart

    2009-05-01

    Before the period of galactic formation the uiverse consisted of a vast number of pre-formed systems consisting of two or more pre-galactic arms, the arms orbiting each other. As the orbits of the arms decayed the sides of the fore-sections of the arms tangentially collided and joined and thereby forming multi-armed spiral galaxies which began to rotate.The rotation resulted from the conversion of the orbital motion of the individual arms when joined into faster rotational motion of the newly formed galaxy. The spiral arms were maintained by the centripital force of the rapidly rotational motion of the galaxy system. As the rotational motion of the galaxy slowed down the arms of the spiral galaxy collapsed towards the body of the galaxy due to lessening of centripetal force on the arms and elliptical galaxies were formed and with further lessening of galactic rotational motion galactic disks were formed. One can see in galaxies M51, M100, NGC2336 and NGC4939 the galactic arms came from external orbit, not disks or instabilities in support of this theory. Also in support of this theory of galactic evolution is that spiral galaxies rotate faster than ellipticals or disks.

  6. Silicon and Magnesium Isotopes in SiC from AGB Stars

    NASA Astrophysics Data System (ADS)

    Clayton, D. D.; Brown, L. E.

    1992-07-01

    We report the evolution of Si and Mg isotopic abundances in the envelopes of massive (5-8 solar masses) AGB-star models. These have now been demonstrated (Brown and Clayton 1992) to be capable of generating the slope 1.4 correlation between excess ^29Si and excess ^30Si. Figure 1 shows the Si isotopic evolution of a 5.5 solar mass model, which reaches only moderately large delta values in the envelope (paralleling the dashed particle line). The asterisk identifies the transformation to carbon star at low deltas. Figure 1, which in the hard copy appears here, shows AGB 5.5 solar mass Si evolution and mass loss. For the first time we are presenting the mass of envelope lost (in wind) as a function of the ^30Si excess. When this star entered its superwind phase it lost most of its mass, and inefficient dredgeup had resulted in deltas near only 100o/oo, as in the large SiC particles. Because the remaining envelope mass is small, little material is lost subsequently on the road to larger deltas. As a result, values of ^30delta near 100 characterize most of the lost mass, showing that STARDUST SiC need not have huge ^30delta. However, changing the prescription for dredgeup or mass-loss rate can greatly alter this. A 6.5 solar mass AGB star lost its superwind near ^30delta = 1600 even with the same dredgeup prescription, showing that other star parameters can have a large influence on ^30delta through their effect on the dredgeup. This needs much more study before we can conclude the true provenance of the meteoritic SiC particles. Because the Mg isotopes also undergo large isotopic evolution in those models, we ask whether that evolution may somehow obscure the amount of live ^26Al that is inferred to have decayed in situ within these STARDUST particles. To the contrary, we show that this peak in mass loss (Fig. 1) occurs with ^25delta = 2 ^26delta, but finishes with ^26delta = 2 ^25delta, simulating mass fractionation at the end. Most of this Mg isotopic evolution is

  7. Galactic planetary science.

    PubMed

    Tinetti, Giovanna

    2014-04-28

    Planetary science beyond the boundaries of our Solar System is today in its infancy. Until a couple of decades ago, the detailed investigation of the planetary properties was restricted to objects orbiting inside the Kuiper Belt. Today, we cannot ignore that the number of known planets has increased by two orders of magnitude nor that these planets resemble anything but the objects present in our own Solar System. Whether this fact is the result of a selection bias induced by the kind of techniques used to discover new planets--mainly radial velocity and transit--or simply the proof that the Solar System is a rarity in the Milky Way, we do not know yet. What is clear, though, is that the Solar System has failed to be the paradigm not only in our Galaxy but even 'just' in the solar neighbourhood. This finding, although unsettling, forces us to reconsider our knowledge of planets under a different light and perhaps question a few of the theoretical pillars on which we base our current 'understanding'. The next decade will be critical to advance in what we should perhaps call Galactic planetary science. In this paper, I review highlights and pitfalls of our current knowledge of this topic and elaborate on how this knowledge might arguably evolve in the next decade. More critically, I identify what should be the mandatory scientific and technical steps to be taken in this fascinating journey of remote exploration of planets in our Galaxy.

  8. Galactic planetary science

    PubMed Central

    Tinetti, Giovanna

    2014-01-01

    Planetary science beyond the boundaries of our Solar System is today in its infancy. Until a couple of decades ago, the detailed investigation of the planetary properties was restricted to objects orbiting inside the Kuiper Belt. Today, we cannot ignore that the number of known planets has increased by two orders of magnitude nor that these planets resemble anything but the objects present in our own Solar System. Whether this fact is the result of a selection bias induced by the kind of techniques used to discover new planets—mainly radial velocity and transit—or simply the proof that the Solar System is a rarity in the Milky Way, we do not know yet. What is clear, though, is that the Solar System has failed to be the paradigm not only in our Galaxy but even ‘just’ in the solar neighbourhood. This finding, although unsettling, forces us to reconsider our knowledge of planets under a different light and perhaps question a few of the theoretical pillars on which we base our current ‘understanding’. The next decade will be critical to advance in what we should perhaps call Galactic planetary science. In this paper, I review highlights and pitfalls of our current knowledge of this topic and elaborate on how this knowledge might arguably evolve in the next decade. More critically, I identify what should be the mandatory scientific and technical steps to be taken in this fascinating journey of remote exploration of planets in our Galaxy. PMID:24664916

  9. Galactic planetary science.

    PubMed

    Tinetti, Giovanna

    2014-04-28

    Planetary science beyond the boundaries of our Solar System is today in its infancy. Until a couple of decades ago, the detailed investigation of the planetary properties was restricted to objects orbiting inside the Kuiper Belt. Today, we cannot ignore that the number of known planets has increased by two orders of magnitude nor that these planets resemble anything but the objects present in our own Solar System. Whether this fact is the result of a selection bias induced by the kind of techniques used to discover new planets--mainly radial velocity and transit--or simply the proof that the Solar System is a rarity in the Milky Way, we do not know yet. What is clear, though, is that the Solar System has failed to be the paradigm not only in our Galaxy but even 'just' in the solar neighbourhood. This finding, although unsettling, forces us to reconsider our knowledge of planets under a different light and perhaps question a few of the theoretical pillars on which we base our current 'understanding'. The next decade will be critical to advance in what we should perhaps call Galactic planetary science. In this paper, I review highlights and pitfalls of our current knowledge of this topic and elaborate on how this knowledge might arguably evolve in the next decade. More critically, I identify what should be the mandatory scientific and technical steps to be taken in this fascinating journey of remote exploration of planets in our Galaxy. PMID:24664916

  10. 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.

  11. 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.

  12. NIRSPEC observations of the galactic center

    NASA Astrophysics Data System (ADS)

    Figer, Donald F.; McLean, Ian S.; Becklin, Eric E.; Graham, James R.; Larkin, James E.; Levenson, N. A.; Teplitz, Harry I.

    2000-06-01

    We report NIRSPEC/Keck observations of the Galactic Center obtained in both low and high resolution modes under excellent seeing conditions. The data were obtained as part of the NIRSPEC commissioning program and will be used to determine: 1) the nature of the stars in the central 0.02 pc, 2) the velocities and accelerations of stars around the central black hole, 3) the velocities of ionized gas in the central parsec, 4) the extent of the main sequence population and star formation history in central parsec, 5) the mass magnitude relation and initial mass function in the Arches cluster, 6) the nature of the MIR sources in the central parsec and Quintuplet clusters, 7) the physical parameters of stellar atmosphere/winds of super luminous stars, and 8) the metallicity in the GC as inferred from observations of red supergiants, red giants, and hot stars. We present a sample of these data, including a high resolution slit scan movie of the central parsec, and show how they can be used to vastly improve the current state of the art in the related science topics. Further, we discuss preliminary results concerning the nature of the central cusp stars and the resultant implications for star formation near a supermassive black hole.

  13. Red Sky with Red Mesa

    ScienceCinema

    None

    2016-07-12

    The Red Sky/Red Mesa supercomputing platform dramatically reduces the time required to simulate complex fuel models, from 4-6 months to just 4 weeks, allowing researchers to accelerate the pace at which they can address these complex problems. Its speed also reduces the need for laboratory and field testing, allowing for energy reduction far beyond data center walls.

  14. Red Sky with Red Mesa

    SciTech Connect

    2011-04-14

    The Red Sky/Red Mesa supercomputing platform dramatically reduces the time required to simulate complex fuel models, from 4-6 months to just 4 weeks, allowing researchers to accelerate the pace at which they can address these complex problems. Its speed also reduces the need for laboratory and field testing, allowing for energy reduction far beyond data center walls.

  15. Red Capes, Red Herrings, and Red Flags.

    ERIC Educational Resources Information Center

    Fiske, Donald W.

    The argument that the personality structures obtained from retrospective ratings reflect semantic similarity structures has been as provocative as a red cape in the bull ring. High congruence between those two kinds of structures seems well established. What is less clear is how and why those structures differ from that for immediate judgments of…

  16. Active galactic nuclei as scaled-up Galactic black holes.

    PubMed

    McHardy, I M; Koerding, E; Knigge, C; Uttley, P; Fender, R P

    2006-12-01

    A long-standing question is whether active galactic nuclei (AGN) vary like Galactic black hole systems when appropriately scaled up by mass. If so, we can then determine how AGN should behave on cosmological timescales by studying the brighter and much faster varying Galactic systems. As X-ray emission is produced very close to the black holes, it provides one of the best diagnostics of their behaviour. A characteristic timescale--which potentially could tell us about the mass of the black hole--is found in the X-ray variations from both AGN and Galactic black holes, but whether it is physically meaningful to compare the two has been questioned. Here we report that, after correcting for variations in the accretion rate, the timescales can be physically linked, revealing that the accretion process is exactly the same for small and large black holes. Strong support for this linkage comes, perhaps surprisingly, from the permitted optical emission lines in AGN whose widths (in both broad-line AGN and narrow-emission-line Seyfert 1 galaxies) correlate strongly with the characteristic X-ray timescale, exactly as expected from the AGN black hole masses and accretion rates. So AGN really are just scaled-up Galactic black holes.

  17. Active galactic nuclei as scaled-up Galactic black holes.

    PubMed

    McHardy, I M; Koerding, E; Knigge, C; Uttley, P; Fender, R P

    2006-12-01

    A long-standing question is whether active galactic nuclei (AGN) vary like Galactic black hole systems when appropriately scaled up by mass. If so, we can then determine how AGN should behave on cosmological timescales by studying the brighter and much faster varying Galactic systems. As X-ray emission is produced very close to the black holes, it provides one of the best diagnostics of their behaviour. A characteristic timescale--which potentially could tell us about the mass of the black hole--is found in the X-ray variations from both AGN and Galactic black holes, but whether it is physically meaningful to compare the two has been questioned. Here we report that, after correcting for variations in the accretion rate, the timescales can be physically linked, revealing that the accretion process is exactly the same for small and large black holes. Strong support for this linkage comes, perhaps surprisingly, from the permitted optical emission lines in AGN whose widths (in both broad-line AGN and narrow-emission-line Seyfert 1 galaxies) correlate strongly with the characteristic X-ray timescale, exactly as expected from the AGN black hole masses and accretion rates. So AGN really are just scaled-up Galactic black holes. PMID:17151661

  18. 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,…

  19. JASMINE: galactic structure surveyor

    NASA Astrophysics Data System (ADS)

    Gouda, Naoteru; Kobayashi, Yukiyasu; Yamada, Yoshiyuki; Yano, Taihei; Tsujimoto, Takuji; Suganuma, Masahiro; Niwa, Yoshito; Yamauchi, Masahiro; Kawakatsu, Yasuhiro; Matsuhara, Hideo; Noda, Atsushi; Tsuiki, Atsuo; Utashima, Masayoshi; Ogawa, Akira

    2006-06-01

    We introduce a Japanese plan of infrared(z-band:0.9μm) space astrometry(JASMINE-project). JASMINE is the satellite (Japan Astrometry Satellite Mission for INfrared Exploration) which will measure distances and apparent motions of stars around the center of the Milky Way with yet unprecedented precision. It will measure parallaxes, positions with the accuracy of 10 micro-arcsec and proper motions with the accuracy of ~ 4microarcsec/ year for stars brighter than z=14mag. JASMINE can observe about ten million stars belonging to the bulge components of our Galaxy, which are hidden by the interstellar dust extinction in optical bands. Number of stars with σ/π < 0.1 in the direction of the Galactic central bulge is about 1000 times larger than those observed in optical bands, where π is a parallax and σ is an error of the parallax. With the completely new "map of the bulge in the Milky Way", it is expected that many new exciting scientific results will be obtained in various fields of astronomy. Presently, JASMINE is in a development phase, with a target launch date around 2015. We adopt the following instrument design of JASMINE in order to get the accurate positions of many stars. A 3-mirrors optical system(modified Korsch system)with a primary mirror of~ 0.85m is one of the candidate for the optical system. On the astro-focal plane, we put dozens of new type of CCDs for z-band to get a wide field of view. The accurate measurements of the astrometric parameters requires the instrument line-of-sight highly stability and the opto-mechanical highly stability of the payload in the JASMINE spacecraft. The consideration of overall system(bus) design is now going on in cooperation with Japan Aerospace Exploration Agency(JAXA).

  20. Galactic Habitable Orbits

    NASA Astrophysics Data System (ADS)

    Rahimi, A.; Mao, S.; Kawata, D.

    2014-03-01

    The fossil record shows that the Earth has experienced several mass extinctions over the past 500 million years1, and it has been suggested that there is a periodicity in extinction events on timescales of tens1 and/or hundreds of millions of years. Various hypotheses have been proposed to explain the cause of the mass extinctions, including the suggestion that the Earth's ozone layer may have been destroyed by intense radiation from a nearby supernovae2- 3, exposing the Earth's surface to damaging UV radiation. Recent observations of cores taken from the ocean floor revealed atoms of a very rare isotope of iron (60Fe) believed to have arrived on Earth around 2 million years ago as fallout from a nearby supernovae4. Astronomical evidence for that past supernovae was recently found in the debris of a young cluster of massive stars5, by tracing its past orbit, putting it at the right place at the right time to explain the mild extinction event. Here we report new high-resolution (both in space and time) N-body chemodynamical simulations (carried out with our novel code GCD+6) of the evolution of a model Milky Way Galaxy, tracing the orbit of èsun-like' stars over a 500 million year period, checking the proximity to supernovae throughout the history of the orbit and comparing the times when this occurs with past mass extinctions on Earth. We additionally explain the important effects of the spiral arm pattern, radial migration of stars and Galactic chemistry on habitability.

  1. A Disturbed Galactic Duo

    NASA Astrophysics Data System (ADS)

    2011-04-01

    The galaxies in this cosmic pairing, captured by the Wide Field Imager on the MPG/ESO 2.2-metre telescope at the La Silla Observatory in Chile, display some curious features, demonstrating that each member of the duo is close enough to feel the distorting gravitational influence of the other. The gravitational tug of war has warped the spiral shape of one galaxy, NGC 3169, and fragmented the dust lanes in its companion NGC 3166. Meanwhile, a third, smaller galaxy to the lower right, NGC 3165, has a front-row seat to the gravitational twisting and pulling of its bigger neighbours. This galactic grouping, found about 70 million light-years away in the constellation Sextans (The Sextant), was discovered by the English astronomer William Herschel in 1783. Modern astronomers have gauged the distance between NGC 3169 (left) and NGC 3166 (right) as a mere 50 000 light-years, a separation that is only about half the diameter of the Milky Way galaxy. In such tight quarters, gravity can start to play havoc with galactic structure. Spiral galaxies like NGC 3169 and NGC 3166 tend to have orderly swirls of stars and dust pinwheeling about their glowing centres. Close encounters with other massive objects can jumble this classic configuration, often serving as a disfiguring prelude to the merging of galaxies into one larger galaxy. So far, the interactions of NGC 3169 and NGC 3166 have just lent a bit of character. NGC 3169's arms, shining bright with big, young, blue stars, have been teased apart, and lots of luminous gas has been drawn out from its disc. In NGC 3166's case, the dust lanes that also usually outline spiral arms are in disarray. Unlike its bluer counterpart, NGC 3166 is not forming many new stars. NGC 3169 has another distinction: the faint yellow dot beaming through a veil of dark dust just to the left of and close to the galaxy's centre [1]. This flash is the leftover of a supernova detected in 2003 and known accordingly as SN 2003cg. A supernova of this

  2. A Disturbed Galactic Duo

    NASA Astrophysics Data System (ADS)

    2011-04-01

    The galaxies in this cosmic pairing, captured by the Wide Field Imager on the MPG/ESO 2.2-metre telescope at the La Silla Observatory in Chile, display some curious features, demonstrating that each member of the duo is close enough to feel the distorting gravitational influence of the other. The gravitational tug of war has warped the spiral shape of one galaxy, NGC 3169, and fragmented the dust lanes in its companion NGC 3166. Meanwhile, a third, smaller galaxy to the lower right, NGC 3165, has a front-row seat to the gravitational twisting and pulling of its bigger neighbours. This galactic grouping, found about 70 million light-years away in the constellation Sextans (The Sextant), was discovered by the English astronomer William Herschel in 1783. Modern astronomers have gauged the distance between NGC 3169 (left) and NGC 3166 (right) as a mere 50 000 light-years, a separation that is only about half the diameter of the Milky Way galaxy. In such tight quarters, gravity can start to play havoc with galactic structure. Spiral galaxies like NGC 3169 and NGC 3166 tend to have orderly swirls of stars and dust pinwheeling about their glowing centres. Close encounters with other massive objects can jumble this classic configuration, often serving as a disfiguring prelude to the merging of galaxies into one larger galaxy. So far, the interactions of NGC 3169 and NGC 3166 have just lent a bit of character. NGC 3169's arms, shining bright with big, young, blue stars, have been teased apart, and lots of luminous gas has been drawn out from its disc. In NGC 3166's case, the dust lanes that also usually outline spiral arms are in disarray. Unlike its bluer counterpart, NGC 3166 is not forming many new stars. NGC 3169 has another distinction: the faint yellow dot beaming through a veil of dark dust just to the left of and close to the galaxy's centre [1]. This flash is the leftover of a supernova detected in 2003 and known accordingly as SN 2003cg. A supernova of this

  3. Birthmarks - red

    MedlinePlus

    Strawberry mark; Vascular skin changes; Angioma cavernosum; Capillary hemangioma; Hemangioma simplex ... There are two main categories of birthmarks: Red birthmarks are ... are called vascular birthmarks. Pigmented birthmarks are areas ...

  4. 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

  5. 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

  6. OPACOS: OVRO POST-AGB CO (1-0) EMISSION SURVEY. I. DATA AND DERIVED NEBULAR PARAMETERS

    SciTech Connect

    Sanchez Contreras, C.; Sahai, R.

    2012-11-15

    We have performed interferometric observations of the {sup 12}CO (J = 1-0) emission in a sample of 27 objects spanning different evolutionary stages from the late asymptotic giant branch (late-AGB), through the post-AGB (pAGB) phase, and to the planetary nebula (PN) stage, but dominated by pAGB objects and young PNs ({>=}81%). In this paper (the first in a series) we present our maps and main nebular properties derived for the whole sample. Observations were performed with the Caltech Millimeter Array at the Owens Valley Radio Observatory. The angular resolution obtained in our survey ranges between 2.''3 and 10.''7. The {sup 13}CO and C{sup 18}O (J = 1-0) transitions as well as the 2.6 mm continuum emission have also been observed in several objects. The detection statistics in the {sup 12}CO, {sup 13}CO, C{sup 18}O transitions and 2.6 mm continuum are 89%, 83%, 0%, and 37%, respectively. We report first detections of {sup 12}CO (J = 1-0) emission in 13 targets and confirm emission from several previous marginal detections. The molecular envelope probed by {sup 12}CO (J = 1-0) emission is extended for 18 (out of 24) sources; envelope asymmetries and/or velocity gradients are found in most extended objects. Our data have been used to derive accurate target coordinates and systemic velocities and to characterize the envelope size, morphology, and kinematics. We also provide an estimate of the total molecular mass and the fraction of it contained in fast flows, lower limits to the linear momentum and to the isotopic {sup 12}C/{sup 13}C ratio, as well as the AGB mass-loss rate and timescale for sources with extended CO emission.

  7. 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.

  8. 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

  9. 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.

  10. Super- and massive AGB stars - IV. Final fates - initial-to-final mass relation

    NASA Astrophysics Data System (ADS)

    Doherty, Carolyn L.; Gil-Pons, Pilar; Siess, Lionel; Lattanzio, John C.; Lau, Herbert H. B.

    2015-01-01

    We explore the final fates of massive intermediate-mass stars by computing detailed stellar models from the zero-age main sequence until near the end of the thermally pulsing phase. These super-asymptotic giant branch (super-AGB) and massive AGB star models are in the mass range between 5.0 and 10.0 M⊙ for metallicities spanning the range Z = 0.02-0.0001. We probe the mass limits Mup, Mn and Mmass, the minimum masses for the onset of carbon burning, the formation of a neutron star and the iron core-collapse supernovae, respectively, to constrain the white dwarf/electron-capture supernova (EC-SN) boundary. We provide a theoretical initial-to-final mass relation for the massive and ultra-massive white dwarfs and specify the mass range for the occurrence of hybrid CO(Ne) white dwarfs. We predict EC-SN rates for lower metallicities which are significantly lower than existing values from parametric studies in the literature. We conclude that the EC-SN channel (for single stars and with the critical assumption being the choice of mass-loss rate) is very narrow in initial mass, at most ≈0.2 M⊙. This implies that between ˜2 and 5 per cent of all gravitational collapse supernova are EC-SNe in the metallicity range Z = 0.02-0.0001. With our choice for mass-loss prescription and computed core growth rates, we find, within our metallicity range, that CO cores cannot grow sufficiently massive to undergo a Type 1.5 SN explosion.

  11. Gas clouds in galactic bulges

    SciTech Connect

    Mathews, W.G.; Murray, S.D.

    1987-01-01

    An analytical model is defined for the orbits of gas clouds moving through a low-density, hot resisting medium in a spiral galactic bulge. The model includes a virial equation that accounts for internal and magnetic energy, external self-pressure, self-gravity and tidal and differential shear stresses, and a criterion for assessing the Rayleigh-Taylor stability of clouds moving within a confining medium. Results are discussed from use of the model to predict the orbital decay efficiency of clouds at different radii moving in a galactic bulge similar to that of the Galaxy. 52 references.

  12. The Heliosphere and Galactic Cosmic Rays

    NASA Video Gallery

    The heliosphere deflects galactic cosmic rays from entering the system. Galactic cosmic rays are a very high energy form of particle radiation that are extremely difficult to shield against and are...

  13. Galactic gamma-ray observations and galactic structure

    NASA Technical Reports Server (NTRS)

    Stecker, F. W.

    1975-01-01

    Recent observations of gamma-rays originating in the galactic disk together with radio observations, support an emerging picture of the overall structure of our galaxy with higher interstellar gas densities and star formation rates in a region which corresponds to that of the inner arms. The emerging picture is one where molecular clouds make up the dominant constituent of the interstellar gas in the inner galaxy and play a key role in accounting for the gamma-rays and phenomena associated with the production of young stars and other population 1 objects. In this picture, cosmic rays are associated with supernovae and are primarily of galactic origin. These newly observed phenomena can be understood as consequences of the density wave theories of spiral structure. Based on these new developments, the suggestion is made that a new galactic population class, Population O, be added to the standard Populations 1 and 2 in order to recognize important differences in dynamics and distribution between diffuse galactic H1 and interstellar molecular clouds.

  14. Far-ultraviolet diffuse galactic light

    NASA Technical Reports Server (NTRS)

    Henry, R. C.

    1981-01-01

    Diffuse galactic light is detected at very low galactic latitudes, and useful upper limits are obtained at moderate and high galactic latitudes. Together, these data indicate that the albedo of the interstellar grains is high (a greater than 0.5) and that the grains very strongly (g greater than 0.7) forward-scatter far-ultraviolet radiation.

  15. 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

  16. Particle acceleration on Galactic scales

    NASA Astrophysics Data System (ADS)

    Axford, W. I.

    The history of and current ideas concerning the origin of cosmic rays in the Galaxy and in extragalactic sources are surveyed. The observed properties of Galactic cosmic rays and shock acceleration are discussed. It is argued that shock acceleration in various guises is an essential and conceptually the most economical acceleration mechanism.

  17. The Formation of Galactic Bulges

    NASA Astrophysics Data System (ADS)

    Carollo, C. Marcella; Ferguson, Henry C.; Wyse, Rosemary F. G.

    2000-03-01

    Part I. Introduction: What are galactic bulges?; Part II. The Epoch of Bulge Formation: Origin of bulges; Deep sub-mm surveys: High-z ULIRGs and the formation of spheroids; Ages and metallicities for stars in the galactic bulge; Integrated stellar populations of bulges: First results; HST-NICMOS observations of galactic bulges: Ages and dust; Inside-out bulge formation and the origin of the Hubble sequence; Part III. The Timescales of Bulge Formation: Constraints on the bulge formation timescale from stellar populations; Bulge building with mergers and winds; Role of winds, starbursts, and activity in bulge formation; Dynamical timescales of bulge formation; Part IV. Physical Processes in Bulge Formation: the role of bars for secular bulge formation; Bars and boxy/peanut-shaped bulges: an observational point of view; Boxy- and peanut-shaped bulges; A new class of bulges; The role of secondary bars in bulge formation; Radial transport of molecular gas to the nuclei of spiral galaxies; Dynamical evolution of bulge shapes; Two-component stellar systems: Phase-space constraints; Central NGC 2146 - a firehose-type bending instability?; Bulge formation: the role of the multi-phase ISM; Global evolution of a self-gravitating multi-phase ISM in the central kpc region of galaxies; Part V. Bulge Phenomenology: Bulge-disk decomposition of spiral galaxies in the near-infrared; The triaxial bulge of NGC 1371; The bulge-disk orthogonal decoupling in galaxies: NGC 4698 and NGC 4672; The kinematics and the origin of the ionized gas in NGC 4036; Optically thin thermal plasma in the galactic bulge; X-ray properties of bulges; The host galaxies of radio-loud AGN; The centers of radio-loud early-type galaxies with HST; Central UV spikes in two galactic spheroids; Conference summary: where do we stand?

  18. Studies of Evolved Star Mass Loss: GRAMS Modeling of Red Supergiant and Asymptotic Giant Branch Stars in the Magellanic Clouds

    NASA Astrophysics Data System (ADS)

    Sargent, Benjamin A.; Srinivasan, S.; Riebel, D.; Boyer, M.; Meixner, M.

    2012-01-01

    As proposed in our NASA Astrophysics Data Analysis Program (ADAP) proposal, my colleagues and I are studying mass loss from evolved stars. Such stars lose their own mass in their dying stages, and in their expelled winds they form stardust. To model mass loss from these evolved stars, my colleagues and I have constructed GRAMS: the Grid of Red supergiant and Asymptotic giant branch star ModelS. These GRAMS radiative transfer models are fit to optical through mid-infrared photometry of red supergiant (RSG) stars and asymptotic giant branch (AGB) stars. I will discuss our current studies of mass loss from AGB and RSG stars in the Small Magellanic Cloud (SMC), fitting GRAMS models to the photometry of SMC evolved star candidates identified from the SAGE-SMC (PI: K. Gordon) Spitzer Space Telescope Legacy survey. This work will be briefly compared to similar work we have done for the LMC. I will also discuss Spitzer Infrared Spectrograph (IRS) studies of the dust produced by AGB and RSG stars in the LMC. BAS is grateful for support from the NASA-ADAP grant NNX11AB06G.

  19. 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.

  20. Luminous AGB Stars beyond the Local Group: Tracers of Intermediate-age Populations in the Cen A Group

    NASA Astrophysics Data System (ADS)

    Crnojević, D.; Rejkuba, M.; Grebel, E. K.; da Costa, G.; Jerjen, H.

    2011-09-01

    We investigate the resolved stellar content of three predominantly old and metal-poor early-type dwarf galaxies in the Centaurus A group (at a distance of ˜4 Mpc). Our goal is to estimate the fraction of the intermediate-age populations (IAPs) and the period of most recent star formation from their luminous AGB stars. We combine optical HST/ACS and near-infrared VLT/ISAAC images to identify AGB star candidates. The first dataset provides high-resolution photometry while the second one permits us to disentangle the galaxies’ stellar content from the foreground contamination and to characterize the IAPs. The IAP fraction is found to be very low in the target galaxies (up to ˜15%). We compare the results to our own Local Group.

  1. Galactic arm structure and gamma ray astronomy

    NASA Technical Reports Server (NTRS)

    Bignami, G. F.; Fichtel, C. E.

    1974-01-01

    Unexpectedly high energy gamma radiation over a broad region of the galactic plane in the general direction of the galactic center was observed. A model is proposed wherein the galactic cosmic rays are preferentially located in the high matter density regions of galactic arm segments, as a result of the weight of the matter in these arms tieing the magnetic fields and hence the cosmic rays to these regions. The presently observed galactic gamma ray longitudinal distribution can be explained with the current estimate of the average galactic matter density: if the average arm to interarm matter ratio is five to one for the major arm segments toward the galactic center from the sun; and if the cosmic ray density normalized to its local value is assumed to be directly proportional to the matter density.

  2. Spitzer-IRS Spectroscopic Studies of the Properties of Dust from Oxygen-Rich Asymptotic Giant Branch and Red Supergiant Stars

    NASA Astrophysics Data System (ADS)

    Sargent, Benjamin A.; Speck, A.; Volk, K.; Kemper, C.; Reach, W. T.; Lagadec, E.; Bernard, J.; McDonald, I.; Meixner, M.; Srinivasan, S.

    2014-01-01

    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 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. BAS acknowledges funding from NASA ADAP grant NNX13AD54G.

  3. 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

  4. Radiation Hazard from Galactic Cosmic Rays

    NASA Astrophysics Data System (ADS)

    Farahat, Ashraf

    2006-03-01

    Space radiation is a major hazard to astronauts in long-duration human space explosion. Astronauts are exposed to an enormous amount of radiation during their missions away from the Earth in outer space. Deep space is a rich environment of protons, gamma rays and cosmic rays. A healthy 40 years old man staying on Earth away from large doses of radiation stands a 20% chance of dying from cancer. If the same person travels into a 3- year Mars mission, the added risk should increase by 19%. This indicates that there is 39% chance of having cancer after he comes back to Earth. Female astronaut chances to get cancer is even almost double the above percentage. The greatest threat to astronauts en route to the red planet is galactic cosmic rays (GCR). GCRs penetrate through the skin of spaceships and people like tiny firearm bullets, breaking the strands of DNA molecules, damaging genes, and killing cells. Understanding the nature of the GCRs, their effect on biological cells, and their interactions with different shielding materials is the key point to shield against them in long space missions. In this paper we will present a model to evaluate the biological effects of GCRs and suggestion different ways to shield against them.

  5. 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.

  6. The RGB and AGB Star Nucleosynthesis in 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.

    2013-02-01

    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 18O(p, α)15N and 17O(p, α)14N reactions, respectively, have been extracted, as well as the contribution of the tail of the broad 656 keV resonance in the 18O(p, α)15N reaction inside the Gamow window. 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. As a result, more accurate reaction rates for the 18O(p, α)15N, 17O(p, α)14N, and 17O(p, γ)18F 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 14N/15N found in SiC grains cannot be explained by the revised nuclear reaction rates and remains a serious problem that has not been satisfactorily addressed.

  7. ALMA observations of the Red Rectangle, a preliminary analysis

    NASA Astrophysics Data System (ADS)

    Bujarrabal, V.; Castro-Carrizo, A.; Alcolea, J.; Van Winckel, H.; Sánchez Contreras, C.; Santander-García, M.; Neri, R.; Lucas, R.

    2013-09-01

    Aims: We aim to study equatorial disks in rotation and axial outflows in post-AGB objects so as to disclose the formation and shaping mechanisms in planetary nebulae. So far, both disks and outflows have not been observed simultaneously. Methods: We obtained high-quality ALMA observations of 12CO and 13CO J = 3-2 and 12CO J = 6-5 line emission in the Red Rectangle, the only post-AGB/protoplanetary object for which a disk in rotation has been mapped. Results: These observations provide an unprecedented description of the complex structure of this source. Together with an equatorial disk in rotation, we find a low-velocity outflow that more or less occupies the region situated between the disk and the optical X-shaped nebula. From our observations and preliminary modeling of the data, we confirm the previously known properties of the disk and obtain a first description of the structure, dynamics, and physical conditions of the outflow. Appendix A is available in electronic form at http://www.aanda.org

  8. ALMA observations of the vibrationally excited rotational CO transitionv= 1,J= 3 - 2 towards five AGB stars

    NASA Astrophysics Data System (ADS)

    Khouri, T.; Vlemmings, W. H. T.; Ramstedt, S.; Lombaert, R.; Maercker, M.; De Beck, E.

    2016-11-01

    We report the serendipitous detection with ALMA of the vibrationally-excited pure-rotational CO transition $v=1, J=3-2$ towards five asymptotic giant branch (AGB) stars, $o$ Cet, R Aqr, R Scl, W Aql, and $\\pi^1$ Gru. The observed lines are formed in the poorly-understood region located between the stellar surface and the region where the wind starts, the so-called warm molecular layer. We successfully reproduce the observed lines profiles using a simple model. We constrain the extents, densities, and kinematics of the region where the lines are produced. R Aqr and R Scl show inverse P-Cygni line profiles which indicate infall of material onto the stars. The line profiles of $o$ Cet and R Scl show variability. The serendipitous detection towards these five sources shows that vibrationally-excited rotational lines can be observed towards a large number of nearby AGB stars using ALMA. This opens a new possibility for the study of the innermost regions of AGB circumstellar envelopes.

  9. Pulsational Light Variability in a Sample of Carbon-rich Post-AGB Stars in the Magellanic Clouds

    NASA Astrophysics Data System (ADS)

    Hrivnak, Bruce J.; Lu, W.; Soszynski, I.; Szczerba, R.; Volk, K.

    2013-06-01

    A sample of 17 carbon-rich post-AGB stars has been identified based on Spitzer spectra of candidate objects in the Magellanic Clouds (Volk et al. 2011, ApJ, 735, 127). We have studied the light variability of these using Ogle II and III data for 15 of these that have such data. We find periodic variability in three, with periods of 74, 96, and 158 days; these have F spectral types. These three we compare with the pulsation properties of carbon-rich post-AGB objects (proto-planetary nebulae) in the Galaxy (Hrivnak et al. 2010, ApJ, 709, 1042). The others all vary, but generally with a shorter timescale. The pulsation amplitudes of the variables range from 0.1 to 0.5 mag in I, and are larger in V. In addition, several show long-term, monotonic changes in brightness. Only a few of these have spectra from which to determine spectral types. Based on our study of post-AGB objects in the Galaxy, we would expect the short-term variables to be objects that have evolved to higher temperatures (B stars) on the HR diagram. This research has been supported by the NSF (AST 1009974).

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    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

  11. 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

  12. Link between Mass-loss and Variability Type for AGB Stars?

    NASA Astrophysics Data System (ADS)

    Ivezić, Ž.; Knapp, G. R.

    We find that AGB stars separate in the 25-12 vs. 12-K color-color diagram according to their chemistry (O, S vs. C) and variability type (Miras vs. SRb/Lb). While discrimination according to the chemical composition is not surprising, the separation of Miras from SRb/Lb variables is unexpected. We show that ``standard'' steady-state radiatively driven models provide excellent fits to the color distribution of Miras of all chemical types. However, these models are incapable of explaining the dust emission from O-rich SRb/Lb stars. The models can be altered to fit the data by postulating different optical properties for silicate grains, or by assuming that the dust temperature at the inner envelope radius is significantly lower (300-400 K) than typical condensation temperatures (800-1,000 K), a possibility which is also supported by the detailed characteristics of LRS data. While such lower temperatures are required only for O- and S-rich SRb/Lb stars, they are also consistent with the colors of C-rich SRb/Lb stars. The absence of hot dust for SRb/Lb stars can be interpreted as a recent (order of 100 yr) decrease in the mass-loss rate. The distribution of O-rich SRb/Lb stars in the 25-12 vs. K-12 color-color diagram shows that the mass-loss rate probably resumes again, on similar time scales. It cannot be ruled out that the mass-loss rate is changing periodically on such time scales, implying that the stars might oscillate between the Mira and SRb/Lb phases during their AGB evolution as proposed by Kerschbaum et al. (1996). Such a possibility appears to be supported by recent HST images of the Egg Nebula obtained by Sahai et al. (1997), the discovery of multiple CO winds reported by Knapp et al. (1998), and long-term visual light-curve changes detected for some stars by Mattei (1998).

  13. Link between Mass-loss and Variability Type for AGB Stars?

    NASA Astrophysics Data System (ADS)

    Ivezic, Z.; Knapp, G. R.

    1998-12-01

    We find that AGB stars separate in the 25-12 vs. 12-K color-color diagram according to their chemistry (O, S vs. C) and variability type (Miras vs. SRb/Lb). While discrimination according to the chemical composition is not surprising, the separation of Miras from SRb/Lb variables is unexpected. We show that ``standard'' steady-state radiatively driven models provide excellent fits to the color distribution of Miras of all chemical types. However, these models are incapable of explaining the dust emission from O-rich SRb/Lb stars. The models can be altered to fit the data by postulating different optical properties for silicate grains, or by assuming that the dust temperature at the inner envelope radius is significantly lower (300-400 K) than typical condensation temperatures (800-1000 K), a possibility which is also supported by the detailed characteristics of LRS data. While such lower temperatures are required only for O- and S-rich SRb/Lb stars, they are also consistent with the colors of C-rich SRb/Lb stars. The absence of hot dust for SRb/Lb stars can be interpreted as a recent (order of 100 yr) decrease in the mass-loss rate. The distribution of O-rich SRb/Lb stars in the 25-12 vs. K-12 color-color diagram shows that the mass-loss rate probably resumes again, on similar time scales. It cannot be ruled out that the mass-loss rate is changing periodically on such time scales, implying that the stars might oscillate between the Mira and SRb/Lb phases during their AGB evolution as proposed by Kerschbaum et al. (1996). Such a possibility appears to be supported by recent HST images of the Egg Nebula obtained by Sahai et al. (1997), the discovery of multiple CO winds reported by Knapp et al. (1998), and long-term visual light-curve changes detected for some stars by Mattei (1998).

  14. Shielding against galactic cosmic rays

    NASA Technical Reports Server (NTRS)

    Schimmerling, W.; Wilson, J. W.; Nealy, J. E.; Thibeault, S. A.; Cucinotta, F. A.; Shinn, J. L.; Kim, M.; Kiefer, R.

    1996-01-01

    Ions of galactic origin are modified but not attenuated by the presence of shielding materials. Indeed, the number of particles and the absorbed energy behind most shield materials increases as a function of shield thickness. The modification of the galactic cosmic ray composition upon interaction with shielding is the only effective means of providing astronaut protection. This modification is intimately conntected with the shield transport porperties and is a strong function of shield composition. The systematic behavior of the shield properites in terms of microscopic energy absorption events will be discussed. The shield effectiveness is examined with respect to convectional protection practice and in terms of a biological endpoint: the efficiency for reduction of the probability of transformation of shielded C3H1OT1/2 mouse cells. The relative advantage of developing new shielding technologies is discussed in terms of a shield performance as related to biological effect and the resulting uncertainty in estimating astronaut risk.

  15. INTEGRAL Galactic bulge monitoring program

    NASA Astrophysics Data System (ADS)

    Kuulkers, E.; Kouveliotou, C.; van der Horst, A. J.; Belloni, T.; Chenevez, J.; Ibarra, A.; Munoz-Darias, T.; Bazzano, A.; Cadolle Bel, M.; De Cesare, G.; Diaz Trigo, M.; Jourdain, E.; Lubinski, P.; Natalucci, L.; Ness, J. U.; Parmar, A.; Pollock, A. M. T.; Rodriguez, J.; Roques, J. P.; Sanchez-Fernandez; C.; Ubertini, P.; Winkler, C.

    2010-12-01

    The central region of our Galaxy, the Galactic bulge, is a rich host of variable high-energy X-ray and gamma-ray point sources. These sources include bright and relatively faint X-ray transients, X-ray bursters, persistent neutron star and black-hole candidate binaries, high-mass X-ray binaries, etc.. We have a program to monitor the Galactic bulge region regularly and frequently with the gamma-ray observatory INTEGRAL, whenever it is observable. As a service to the scientific community the high-energy light curves of sources present, as well as the images of the region are made available through the WWW at http://integral.esac.esa.int/BULGE/ as soon as possible after the observations have been performed. We show the ongoing results of this exciting program.

  16. MID-INFRARED EXTINCTION AND ITS VARIATION WITH GALACTIC LONGITUDE

    SciTech Connect

    Gao Jian; Jiang, B. W.; Li Aigen E-mail: bjiang@bnu.edu.c

    2009-12-10

    Based on the data obtained from the Spitzer/Galactic Legacy Infrared Midplane Survey Extraordinaire (GLIPMSE) Legacy Program and the Two Micron All Sky Survey (2MASS) project, we derive the extinction in the four IRAC bands, [3.6], [4.5], [5.8], and [8.0] mum, relative to the 2MASS K{sub s} band (at 2.16 mum) for 131 GLIPMSE fields along the Galactic plane within |l| <= 65 deg., using red giants and red clump giants as tracers. As a whole, the mean extinction in the IRAC bands (normalized to the 2MASS K{sub s} band), A{sub [3.6]}/A{sub K{sub s}}approx0.63+-0.01, A{sub [4.5]}/A{sub K{sub s}}approx0.57+-0.03, A{sub [5.8]}/A{sub K{sub s}}approx0.49+-0.03, A{sub [8.0]}/A{sub K{sub s}}approx0.55+-0.03, exhibits little variation with wavelength (i.e., the extinction is somewhat flat or gray). This is consistent with previous studies and agrees with that predicted from the standard interstellar grain model for R{sub V} = 5.5 by Weingartner and Draine. As far as individual sightline is concerned, however, the wavelength dependence of the mid-infrared interstellar extinction A{sub l}ambda/A{sub K{sub s}} varies from one sightline to another, suggesting that there may not exist a 'universal' IR extinction law. We, for the first time, demonstrate the existence of systematic variations of extinction with Galactic longitude which appears to correlate with the locations of spiral arms as well as with the variation of the far-infrared luminosity of interstellar dust.

  17. Inversions for axisymmetric galactic disks

    NASA Astrophysics Data System (ADS)

    Hiotelis, N.; Patsis, P. A.

    1993-08-01

    We use two models for the distribution function to solve an inverse problem for axisymmetric disks. These systems may be considered - under certain assumptions - as galactic disks. In some cases the solutions of the resulting integral equations are simple, which allows the determination of the kinematic properties of self-consistent models for these systems. These properties for then = 1 Toomre disk are presented in this study.

  18. Constraints on galactic wind models

    NASA Astrophysics Data System (ADS)

    Meiksin, Avery

    2016-09-01

    Observational implications are derived for two standard models of supernovae-driven galactic winds: a freely expanding steady-state wind and a wind sourced by a self-similarly expanding superbubble including thermal heat conduction. It is shown that, for the steady-state wind, matching the measured correlation between the soft X-ray luminosity and star formation rate of starburst galaxies is equivalent to producing a scaled wind mass-loading factor relative to the star formation rate of 0.5-3, in agreement with the amount inferred from metal absorption line measurements. The match requires the asymptotic wind velocity v∞ to scale with the star formation rate dot{M}_{ast } (in M⊙ yr-1) approximately as v_∞ ≃ (700-1000) {{km s^{-1}}} {dot{M}_{ast }}^{1/6}. The implied mass injection rate is close to the amount naturally provided by thermal evaporation from the wall of a superbubble in a galactic disc, suggesting that thermal evaporation may be a major source of mass loading. The predicted mass-loading factors from thermal evaporation within the galactic disc alone, however, are somewhat smaller, 0.2-2, so that a further contribution from cloud ablation or evaporation within the wind may be required. Both models may account for the 1.4 GHz luminosity of unresolved radio sources within starburst galaxies for plausible parameters describing the distribution of relativistic electrons. Further observational tests to distinguish the models are suggested.

  19. Densities of Galactic Center Clouds

    NASA Astrophysics Data System (ADS)

    Barnes, Jonathan; Mills, Elisabeth A. C.; Morris, Mark R.

    2015-04-01

    The central 300 parsecs of the Galaxy is full of giant molecular clouds containing 107 solar masses worth of gas. However, our Galactic center is not forming as many stars as we think it can, based on the amount of molecular gas in this region. By studying the densities of the Galactic center clouds we hope to better understand why there is not much star formation occurring. Using data from the Green Bank and MOPRA telescopes we have observed multiple rotation transitions of HC3N and its 13C isotopologues. By measuring the integrated intensity of the HC3 N we are able to calculate the densities of these giant molecular clouds. The measured intensities are used with a radiative transfer code called RADEX, to determine volume densities. Our initial results suggest that there may be either less dense or cooler gas in these clouds that previously thought. If there is a significant quantity of gas less dense than 104 molecules/cm3 , this could explain the lack of ongoing star formation in these clouds, and might also suggest a shorter timescale for dynamical disruption of theses clouds. In the future, we plan to improve these results by observing additional HC3N transitions, allowing us better to constrain the relative contributions of multiple temperature and density components in Galactic center clouds.

  20. A 1.2 mm MAMBO survey of post-AGB stars

    NASA Astrophysics Data System (ADS)

    Buemi, C. S.; Umana, G.; Trigilio, C.; Leto, P.

    2007-02-01

    Aims:We performed a millimetric survey of a sample of 24 post-AGB stars aimed at searching for emission from circumstellar matter, in order to investigate the physical properties of the outer parts of the envelopes. Methods: The observations were conducted using the 37-channel Max-Planck Millimeter Bolometer array at the 30-meter IRAM telescope. The continuum emission toward the detected sources was used to quantify the mass of the emitting dust. We combined our observations with data available in the literature to construct the spectral energy distribution (SED) of the sources. When the observational data covered a spectral range wide enough, some properties of circumstellar envelopes were derived by comparison with spectra computed using a radiative transfer code. Results: Of the 24 objects in our sample, we detected millimetric continuum emission toward 11 sources. Two other sources were detected at a flux level close to 3σ. The derived circumstellar dust masses range between 0.4 and 24 × 10-4 M⊙, but these results are affected by the uncertainty about the source distances. The parameters derived from the SED fits are consistent with the values characteristic of this kind of object. As confirmed from the flux density extrapolated in the first light channels of the Atacama Large Millimetric Array, these sources could be good targets for future high-resolution mapping with the ALMA facility.

  1. Watching Stars Evolve: Rapid Evolutionary Changes of the Post-AGB Star - FG SGE

    NASA Astrophysics Data System (ADS)

    Guinan, E. F.; Efimov, Yu. S.; Margheim, S. J.

    The variable post-AGB star FG Sge has provided an unique opportunity to study phenomenon which may be characteristic of the post-PN stage of stellar evolution. FG Sge is the central star in the 36-arcsec PN He 1-5 that over the last 50 yrs has been undergoing rapid evolutionary changes. Most notable are changes in temperature, luminosity, chemical composition and pulsation period. Starting in mid-1992, the star has undergone several large dimming events from which it still has yet to recover. These events closely resemble the dimming events commonly observed in R CrB stars which result from dust formation in ejected envelopes. From all the evidence, it now appears that FG Sge has evolved into a R CrB star. In this paper we summarize the recent photometric history of the FG Sge from UBVRI photometry obtained during 1990-1997. We combine these data with earlier photometry to define the star's light bevavior over the last 100 yrs. The photometry is also combined with available spectroscopic polarimetric, and IR observations. Particlar attention is given to comparing FG Sge's post-dimming behavoir with contemporaneous observations of R CrB itself, also done on the same photometric system.

  2. The Arabidopsis adaptor protein AP-3μ interacts with the G-protein β subunit AGB1 and is involved in abscisic acid regulation of germination and post-germination development.

    PubMed

    Kansup, Jeeraporn; Tsugama, Daisuke; Liu, Shenkui; Takano, Tetsuo

    2013-12-01

    Heterotrimeric G-proteins (G-proteins) have been implicated in ubiquitous signalling mechanisms in eukaryotes. In plants, G-proteins modulate hormonal and stress responses and regulate diverse developmental processes. However, the molecular mechanisms of their functions are largely unknown. A yeast two-hybrid screen was performed to identify interacting partners of the Arabidopsis G-protein β subunit AGB1. One of the identified AGB1-interacting proteins is the Arabidopsis adaptor protein AP-3µ. The interaction between AGB1 and AP-3µ was confirmed by an in vitro pull-down assay and bimolecular fluorescence complementation assay. Two ap-3µ T-DNA insertional mutants were found to be hyposensitive to abscisic acid (ABA) during germination and post-germination growth, whereas agb1 mutants were hypersensitive to ABA. During seed germination, agb1/ap-3µ double mutants were more sensitive to ABA than the wild type but less sensitive than agb1 mutants. However, in post-germination growth, the double mutants were as sensitive to ABA as agb1 mutants. These data suggest that AP-3µ positively regulates the ABA responses independently of AGB1 in seed germination, while AP-3µ does require AGB1 to regulate ABA responses during post-germination growth.

  3. Diffuse Galactic Light in the Field of the Translucent High Galactic Latitude Cloud MBM32

    NASA Astrophysics Data System (ADS)

    Ienaka, N.; Kawara, K.; Matsuoka, Y.; Sameshima, H.; Oyabu, S.; Tsujimoto, T.; Peterson, B. A.

    2013-04-01

    We have conducted B-, g-, V-, and R-band imaging in a 45' × 40' field containing part of the high Galactic latitude translucent cloud MBM32, and correlated the intensity of diffuse optical light S ν(λ) with that of 100 μm emission S ν(100 μm). A χ2 minimum analysis is applied to fit a linear function to the measured correlation and derive the slope parameter b(λ) = ΔS ν(λ)/ΔS ν(100 μm) of the best-fit linear function. Compiling a sample by combining our b(λ) and published ones, we show that the b(λ) strength varies from cloud to cloud by a factor of four. Finding that b(λ) decreases as S ν(100 μm) increases in the sample, we suggest that a nonlinear correlation including a quadratic term of S ν(100 μm)2 should be fitted to the measured correlation. The variation of optical depth, which is AV = 0.16-2.0 in the sample, can change b(λ) by a factor of 2-3. There would be some contribution to the large b(λ) variation from the forward-scattering characteristic of dust grains which is coupled to the non-isotropic interstellar radiation field (ISRF). Models of the scattering of diffuse Galactic light (DGL) underestimate the b(λ) values by a factor of two. This could be reconciled by deficiency in UV photons in the ISRF or by a moderate increase in dust albedo. Our b(λ) spectrum favors a contribution from extended red emission (ERE) to the diffuse optical light; b(λ) rises from B to V faster than the models, seems to peak around 6000 Å and decreases toward long wavelengths. Such a characteristic is expected from the models in which the DGL is combined with ERE.

  4. 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.

  5. SAS-2 galactic gamma ray results, 1

    NASA Technical Reports Server (NTRS)

    Thompson, D. J.; Fichtel, C. E.; Hartman, R. C.; Kniffen, D. A.; Bignami, G. F.; Lamb, R. C.; Oegelman, H.; Oezel, M. E.; Tuemer, T.

    1976-01-01

    Continuing analysis of the data from the SAS-2 high energy gamma-ray experiment has produced an improved picture of the sky at photon energies above 35 MeV. On a large scale, the diffuse emission from the galactic plane is the dominant feature observed by SAS-2. This galactic plane emission is most intense between galactic longitude 310 and 45 deg, corresponding to a region within 7kpc of the galactic center. Within the high-intensity region, SAS-2 observes peaks around galactic longitudes 315 deg, 330 deg, 345 deg, 0 deg, and 35 deg. These peaks appear to be correlated with such galactic features and components as molecular hydrogen, atomic hydrogen, magnetic fields, cosmic ray concentrations, and photon fields.

  6. ATOMIC HYDROGEN IN A GALACTIC CENTER OUTFLOW

    SciTech Connect

    McClure-Griffiths, N. M.; Green, J. A.; Hill, A. S.; Lockman, F. J.; Dickey, J. M.; Gaensler, B. M.; Green, A. J.

    2013-06-10

    We describe a population of small, high-velocity, atomic hydrogen clouds, loops, and filaments found above and below the disk near the Galactic center. The objects have a mean radius of 15 pc, velocity widths of {approx}14 km s{sup -1}, and are observed at |z| heights up to 700 pc. The velocity distribution of the clouds shows no signature of Galactic rotation. We propose a scenario where the clouds are associated with an outflow from a central star-forming region at the Galactic center. We discuss the clouds as entrained material traveling at {approx}200 km s{sup -1} in a Galactic wind.

  7. 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.

  8. Development of a near infrared camera for conducting a survey of northern Galactic Cepheid variable stars

    NASA Astrophysics Data System (ADS)

    Monson, Andrew John

    In the past few decades there has been growing realization that the Cepheid Near-Infrared (NIR) Period-Luminosity (PL) relation is superior to the Optical PL relation, however, there has been little to no new NIR data gathered on Galactic Cepheids despite the growing popularity and availability of NIR detectors. Galactic Cepheids are, in general, too bright to be observed by telescopes with apertures larger than 1-meter and most NIR detector arrays are too costly to justify placing on sub-1m class telescopes. I describe the development of a near-infrared (NIR) camera for the University of Wyoming's 0.6m telescope at Red Buttes Observatory. The camera, known as BIRCAM (Buttes InfraRed CAMera), was conceived to be a temporary, inexpensive test-bed instrument designed to test the electronic and cryo-mechanical components of another large-scale NIR imaging camera. BIRCAM was designed to make use of a CMOS HgCdTe Hawaii-2 detector array sensitive from 0.9-2.5 microns and during its relatively short lifetime I used BIRCAM to synoptically survey 130 fields containing Galactic Cepheids. These data will help provide the means to calibrate the NIR Cepheid Period-Luminosity Relation. The Cepheid Period-Luminosity (PL) Relation is fundamental to determining distances to nearby galaxies and as such is essential to calibrating the distance scale of the Universe. The accuracy and precision of the distance scale is determined in part by the accuracy and precision of the Galactic PL relation. Observations of Galactic Cepheids in the NIR play an important role in reducing systematic errors inherent to optical observations. The future calibration and refinement of the distance scale relies on providing accurate NIR photometry of Galactic Cepheid Variable Stars. Current photometric studies of Galactic Cepheids in the NIR are limited in size and homo-geneity. The goal of this project is to provide a homogenous photometric study that triples the number of well-sampled Galactic Cepheid

  9. THE GALACTIC CENTER: NOT AN ACTIVE GALACTIC NUCLEUS

    SciTech Connect

    An, Deokkeun; Ramirez, Solange V.; Sellgren, Kris

    2013-06-01

    We present 10 {mu}m-35 {mu}m Spitzer spectra of the interstellar medium in the Central Molecular Zone (CMZ), the central 210 pc Multiplication-Sign 60 pc of the Galactic center (GC). We present maps of the CMZ in ionic and H{sub 2} emission, covering a more extensive area than earlier spectroscopic surveys in this region. The radial velocities and intensities of ionic lines and H{sub 2} suggest that most of the H{sub 2} 0-0 S(0) emission comes from gas along the line-of-sight, as found by previous work. We compare diagnostic line ratios measured in the Spitzer Infrared Nearby Galaxies Survey to our data. Previous work shows that forbidden line ratios can distinguish star-forming galaxies from low-ionization nuclear emission-line regions (LINERs) and active galactic nuclei (AGNs). Our GC line ratios agree with star-forming galaxies and not with LINERs or AGNs.

  10. HEGRA Observations of Galactic Sources

    NASA Astrophysics Data System (ADS)

    Völk, H.; Hegea Collaboration

    2000-06-01

    In this talk I will first give a summary of the observations of expected Galactic TeV gamma-ray sources with the HEGRA CT-Sytem since the Kruger Park Workshop in 1997. Then I will go into some detail regarding the observations of Supernova Remnants (SNRs), especially those of Tycho's SNR and of Cas A. The emphasis will not be on all aspects of these published data. I will rather review the selection of these observational targets, and discuss some of the physical implications of the results.

  11. HEGRA observations of Galactic sources

    NASA Astrophysics Data System (ADS)

    HEGRA Collaboration

    2000-06-01

    In this talk I will first give a summary of the observations of expected Galactic TeV γ-ray sources with the HEGRA CT-System since the Kruger Park Workshop in 1997. Then I will go into some detail regarding the observations of Supernova Remnants (SNRs), especially those of Tycho's SNR and of Cas A. The emphasis will not be on all aspects of these published data. I will rather review the selection of these observational targets, and discuss some of the physical implications of the results. .

  12. Exploring masses and CNO surface abundances of red giant stars

    NASA Astrophysics Data System (ADS)

    Halabi, Ghina M.; Eid, Mounib El

    2015-08-01

    A grid of evolutionary sequences of stars in the mass range 1.2-7M⊙, with solar-like initial composition is presented. We focus on this mass range in order to estimate the masses and calculate the CNO surface abundances of a sample of observed red giants. The stellar models are calculated from the zero-age main sequence till the early asymptotic giant branch (AGB) phase. Stars of M ≤ 2.2M⊙ are evolved through the core helium flash. In this work, an approach is adopted that improves the mass determination of an observed sample of 21 RGB and early AGB stars. This approach is based on comparing the observationally derived effective temperatures and absolute magnitudes with the calculated values based on our evolutionary tracks in the Hertzsprung-Russell diagram. A more reliable determination of the stellar masses is achieved by using evolutionary tracks extended to the range of observation. In addition, the predicted CNO surface abundances are compared to the observationally inferred values in order to show how far standard evolutionary calculation can be used to interpret available observations and to illustrate the role of convective mixing. We find that extra mixing beyond the convective boundary determined by the Schwarzschild criterion is needed to explain the observational oxygen isotopic ratios in low-mass stars. The effect of recent determinations of proton capture reactions and their uncertainties on the 16O/17O and 14N/15N ratios is also shown. It is found that the 14N( p, γ)15O reaction is important for predicting the 14N/15N ratio in red giants.

  13. The color dependent morphology of the post-AGB star HD 161796

    NASA Astrophysics Data System (ADS)

    Min, M.; Jeffers, S. V.; Canovas, H.; Rodenhuis, M.; Keller, C. U.; Waters, L. B. F. M.

    2013-06-01

    Context. Many protoplanetary nebulae show strong asymmetries in their surrounding shells, pointing to asymmetries during the mass loss phase. Questions concerning the origin and the onset of deviations from spherical symmetry are important for our understanding of the evolution of these objects. Here we focus on the circumstellar shell of the post-AGB star HD 161796. Aims: We aim to detect signatures of an aspherical outflow, and to derive its properties. Methods: We used the imaging polarimeter the Extreme Polarimeter (ExPo), a visitor instrument at the William Herschel Telescope, to accurately image the dust shell surrounding HD 161796 in various wavelength filters. Imaging polarimetry allows us to separate the faint, polarized, light that comes from circumstellar material from the bright, unpolarized, light from the central star. Results: The shell around HD 161796 is highly aspherical. A clear signature of an equatorial density enhancement can be seen. This structure is optically thick at short wavelengths and changes its appearance to optically thin at longer wavelengths. In the classification of the two different appearances of planetary nebulae from HST images it changes from being classified as DUst-Prominent Longitudinally-EXtended (DUPLEX) at short wavelengths to star-obvious low-level-elongated (SOLE) at longer wavelengths. This strengthens the interpretation that these two appearances are manifestations of the same physical structure. Furthermore, we find that the central star is hotter than often assumed and the relatively high observed reddening is a consequence of circumstellar rather than interstellar extinction. Based 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 Astrofsicaŋsica de Canarias.

  14. Radial-Velocity Analysis of the Post-AGB Star, HD101584

    NASA Astrophysics Data System (ADS)

    Díaz, F.; Hearnshaw, J.; Rosenzweig, P.; Guzman, E.; Sivarani, T.; Parthasarathy, M.

    2007-08-01

    This project concerns the analysis of the periodicity of the radial velocity of the peculiar emission-line supergiant star HD 101584 (F0 Ia), and also we propose a physical model to account for the observations. From its peculiarities, HD 101584 is a star that is in the post-AGB phase. This study is considered as a key to clarify the multiple aspects related with the evolution of the circum-stellar layer associated with this star's last phase. The star shows many lines with P Cygni profiles, including H-alpha, Na D lines in the IR Ca triplet, indicating a mass outflow. For HD 101584 we have performed a detailed study of its radial-velocity variations, using both emission and absorption lines over a wide range of wavelength. We have analyzed the variability and found a periodicity for all types of lines of 144 days, which must arise from the star's membership in a binary system. The data span a period of five consecutive years and were obtained using the 1-m telescope of Mt John Observatory, in New Zealand., with the echelle and Hercules high resolution spectrographs and CCD camera. HD101584 is known to be an IRAS source, and our model suggests it is a proto-planetary nebula, probably with a bipolar outflow and surrounded by a dusty disk as part of a binary system. We have found no evidence for HD101584 to contain a B9 star as found by Bakker et al (1996). A low resolution IUE spectrum shows the absence of any strong UV continuum that would be expected for a B star to be in this system.

  15. Three Dimensional Stellar Kinematics of the Galactic Bar and Disk: Where APOGEE Meets GLIMPSE

    NASA Astrophysics Data System (ADS)

    Benjamin, Robert; Babler, Brian; D'Onghia, Elena; Clarkson, Will; Churchwell, Ed; Kirkpatrick, Davy; Zasowski, Gail; Majewski, Steve

    2016-08-01

    We propose to use the Spitzer Space Telescope to re-image 53 square degrees (fourteen fields) of the inner Galactic plane (galactic longitudes \\|L\\|=6-45 degrees) that have also been targeted by the APOGEE/APOGEE-2 surveys-Sloan III and IV programs to obtain high resolution H band spectroscopy for hundreds of thousands of red giants. We will combine the proposed observations (198 hours) with the original GLIMPSE observations of the Galactic plane in 2004-2005 to measure the proper motions of sources along the Galactic plane over the past decade. When combined with the 43 square degrees of Priority 1 data being obtained for Cycle 12--which cover \\|L\\|< 5 degrees and \\|B\\|<2 degrees, plus Baade's window -we will have proper motion constraints for over 25 million sources. The combination of Spitzer proper motions for millions of sources and APOGEE radial velocities for thousands of sources will be used to constrain models of stellar kinematics for the Galactic bar(s) and disk. We will also use this data to test several bar formation models that have been developed to explain the mysterious 'high-velocity' Milky Way bar stars (Nidever et al 2012b), one of the first APOGEE discoveries. This program will be the most uniform and deep Galactic plane proper motion study as mid-infrared observations are minimally affected by extinction over most of the region we propose to cover. We also expect to be able to find at least 150 high proper motion stars which could be substellar objects and possible micro-lensing candidates against the crowded Galactic disk.

  16. Galactic Archaeology with CoRoT and APOGEE: Creating mock observations from a chemodynamical model

    NASA Astrophysics Data System (ADS)

    Anders, F.; Chiappini, C.; Rodrigues, T. S.; Piffl, T.; Mosser, B.; Miglio, A.; Montalbán, J.; Girardi, L.; Minchev, I.; Valentini, M.; Steinmetz, M.

    2016-09-01

    In a companion paper, we have presented the combined asteroseismic-spectroscopic dataset obtained from CoRoT light curves and APOGEE infra-red spectra for 606 solar-like oscillating red giants in two fields of the Galactic disc (CoRoGEE). We have measured chemical abundance patterns, distances, and ages of these field stars which are spread over a large radial range of the Milky Way's disc. Here we show how to simulate this dataset using a chemodynamical Galaxy model. We also demonstrate how the observation procedure influences the accuracy of our estimated ages.

  17. VizieR Online Data Catalog: Metallicity and kinematics in Galactic bar (Babusiaux+, 2014)

    NASA Astrophysics Data System (ADS)

    Babusiaux, C.; Katz, D.; Hill, V.; Royer, F.; Gomez, A.; Arenou, F.; Combes, F.; Di Matteo, P.; Gilmore, G.; Haywood, M.; Robin, A. C.; Rodriguez-Fernandez, N.; Sartoretti, M.; Schultheis, P.

    2014-01-01

    We observe red clump stars in four fields along the Galactic bar major axis (l=10°, -6°, 6° and b=0°, plus a field at l=0°, b=1°) with low-resolution spectroscopy from FLAMES/GIRAFFE (setup LR08) at the VLT, observing around the CaII triplet. We developed robust methods to extract radial velocity and metallicity estimates from these low signal-to-noise spectra. Results have been derived by fixing atmospheric parameters typical of a red clump star (Teff=4750K, logg=2.5). For some targets, the metallicity could not be derived. (1 data file).

  18. Local Stellar Kinematics from RAVE data - V. Kinematic Investigation of the Galaxy with Red Clump Stars

    NASA Astrophysics Data System (ADS)

    Karaali, S.; Bilir, S.; Ak, S.; Gökçe, E. Yaz; Önal, Ö.; Ak, T.

    2014-02-01

    We investigated the space velocity components of 6 610 red clump (RC) stars in terms of vertical distance, Galactocentric radial distance and Galactic longitude. Stellar velocity vectors are corrected for differential rotation of the Galaxy which is taken into account using photometric distances of RC stars. The space velocity components estimated for the sample stars above and below the Galactic plane are compatible only for the space velocity component in the direction to the Galactic rotation of the thin disc stars. The space velocity component in the direction to the Galactic rotation (V lsr) shows a smooth variation relative to the mean Galactocentric radial distance (Rm ), while it attains its maximum at the Galactic plane. The space velocity components in the direction to the Galactic centre (U lsr) and in the vertical direction (W lsr) show almost flat distributions relative to Rm , with small changes in their trends at Rm ~ 7.5 kpc. U lsr values estimated for the RC stars in quadrant 180° < l ⩽ 270° are larger than the ones in quadrants 0° < l ⩽ 90° and 270° < l ⩽ 360°. The smooth distribution of the space velocity dispersions reveals that the thin and thick discs are kinematically continuous components of the Galaxy. Based on the W lsr space velocity components estimated in the quadrants 0° < l ⩽ 90° and 270° < l ⩽ 360°, in the inward direction relative to the Sun, we showed that RC stars above the Galactic plane move towards the North Galactic Pole, whereas those below the Galactic plane move in the opposite direction. In the case of quadrant 180° < l ⩽ 270°, their behaviour is different, i.e. the RC stars above and below the Galactic plane move towards the Galactic plane. We stated that the Galactic long bar is the probable origin of many, but not all, of the detected features.

  19. Detection of HCN and C2H2 in ISO Spectra of Oxygen-Rich AGB Stars

    NASA Technical Reports Server (NTRS)

    Carbon, Duane F.; Chiar, Jean; Goorvitch, David; Kwak, Dochan (Technical Monitor)

    2002-01-01

    Cool oxygen-rich AGB stars were not expected to have organic molecules like HCN in either their photospheres or circumstellar envelopes (CSEs). The discovery of HCN and CS microwave emission from the shallowest CSE layers of these stars was a considerable surprise and much theoretical effort has been expended in explaining the presence of such organics. To further explore this problem, we have undertaken a systematic search of oxygen-rich AGB stellar spectra in the Infrared Space Observatory (ISO) data archive. Our purposes are to find evidence regarding critical molecular species that could be of value in choosing among the proposed theoretical models, to locate spectral features which might give clues to conditions deeper in the CSEs, and to lay the groundwork for future SIRTF (Space Infrared Telescope Facility) and SOFIA (Stratospheric Observatory for Infrared Astronomy) observations. Using carefully reduced observations, we have detected weak absorption features arising from HCN and possibly C2H2 in a small number of oxygen-rich AGB stars. The most compelling case is NML Cyg which shows both HCN (14 microns) and CO2 (15 microns). VY CMa, a similar star, shows evidence for HCN, but not CO2. Two S-type stars show evidence for the C-H bending transitions: W Aql at 14 microns (HCN) and both W Aql and S Cas at 13.7 microns (C2H2). Both W Aql and S Cas as well as S Lyr, a SC-type star, show 3 micron absorption which may arise from the C-H stretch of HCN and C2H2. In the case of NML Cyg, we show that the HCN and CO2 spectral features are formed in the CSE at temperatures well above those of the outermost CSE layers and derive approximate column densities. In the case of the S-stars, we discuss the evidence for the organic features and their photospheric origin.

  20. Super and massive AGB stars - II. Nucleosynthesis and yields - Z = 0.02, 0.008 and 0.004

    NASA Astrophysics Data System (ADS)

    Doherty, Carolyn L.; Gil-Pons, Pilar; Lau, Herbert H. B.; Lattanzio, John C.; Siess, Lionel

    2014-01-01

    We have computed detailed evolution and nucleosynthesis models for super and massive asymptotic giant branch (AGB) stars over the mass range 6.5-9.0 M⊙ in divisions of 0.5 M⊙ with metallicities Z = 0.02, 0.008 and 0.004. These calculations, in which we find third dredge-up and hot bottom burning, fill the gap between existing low- and intermediate-mass AGB star models and high-mass star models that become supernovae. For the considered metallicities, the composition of the yields is largely dominated by the thermodynamic conditions at the base of the convective envelope rather than by the pollution arising from third dredge-up. We investigate the effects of various uncertainties, related to the mass-loss rate, mixing length parameter, and the treatment of evolution after the envelope instability that develops near the end of the (super)AGB phase. Varying these parameters alters the yields mainly because of their impact on the amount of third dredge-up enrichment, and to a lesser extent on the hot bottom burning conditions. Our models produce significant amounts of 4He, 7Li (depending on the mass-loss formulation) 13C, 14N, 17O, 23Na, 25Mg, as well the radioactive isotope 26Al in agreement with previous investigation. In addition, our results show enrichment of 22Ne, 26Mg and 60Fe, as well as a substantial increase in our proxy neutron capture species representing all species heavier than iron. These stars may provide important contributions to the Galaxy's inventory of the heavier Mg isotopes, 14N, 7Li and 27Al.

  1. Introduction to Galactic Chemical Evolution

    NASA Astrophysics Data System (ADS)

    Matteucci, Francesca

    2016-04-01

    In this lecture I will introduce the concept of galactic chemical evolution, namely the study of how and where the chemical elements formed and how they were distributed in the stars and gas in galaxies. The main ingredients to build models of galactic chemical evolution will be described. They include: initial conditions, star formation history, stellar nucleosynthesis and gas flows in and out of galaxies. Then some simple analytical models and their solutions will be discussed together with the main criticisms associated to them. The yield per stellar generation will be defined and the hypothesis of instantaneous recycling approximation will be critically discussed. Detailed numerical models of chemical evolution of galaxies of different morphological type, able to follow the time evolution of the abundances of single elements, will be discussed and their predictions will be compared to observational data. The comparisons will include stellar abundances as well as interstellar medium ones, measured in galaxies. I will show how, from these comparisons, one can derive important constraints on stellar nucleosynthesis and galaxy formation mechanisms. Most of the concepts described in this lecture can be found in the monograph by Matteucci (2012).

  2. Star formation in Galactic flows

    NASA Astrophysics Data System (ADS)

    Smilgys, Romas; Bonnell, Ian A.

    2016-06-01

    We investigate the triggering of star formation in clouds that form in Galactic scale flows as the interstellar medium passes through spiral shocks. We use the Lagrangian nature of smoothed particle hydrodynamics simulations to trace how the star-forming gas is gathered into self-gravitating cores that collapse to form stars. Large-scale flows that arise due to Galactic dynamics create shocks of the order of 30 km s-1 that compress the gas and form dense clouds (n > several × 102 cm-3) in which self-gravity becomes relevant. These large-scale flows are necessary for creating the dense physical conditions for gravitational collapse and star formation. Local gravitational collapse requires densities in excess of n > 103 cm-3 which occur on size scales of ≈1 pc for low-mass star-forming regions (M < 100 M⊙), and up to sizes approaching 10 pc for higher mass regions (M > 103 M⊙). Star formation in the 250 pc region lasts throughout the 5 Myr time-scale of the simulation with a star formation rate of ≈10-1 M⊙ yr-1 kpc-2. In the absence of feedback, the efficiency of the star formation per free-fall time varies from our assumed 100 per cent at our sink accretion radius to values of <10-3 at low densities.

  3. Special Features of Galactic Dynamics

    NASA Astrophysics Data System (ADS)

    Efthymiopoulos, Christos; Voglis, Nikos; Kalapotharakos, Constantinos

    This is an introductory article to some basic notions and currently open problems of galactic dynamics. The focus is on topics mostly relevant to the so-called `new methods' of celestial mechanics or Hamiltonian dynamics, as applied to the ellipsoidal components of galaxies, i.e., to the elliptical galaxies and to the dark halos and bulges of disk galaxies. Traditional topics such as Jeans theorem, the role of a `third integral' of motion, Nekhoroshev theory, violent relaxation, and the statistical mechanics of collisionless stellar systems are first discussed. The emphasis is on modern extrapolations of these old topics. Recent results from orbital and global dynamical studies of galaxies are then shortly reviewed. The role of various families of orbits in supporting self-consistency, as well as the role of chaos in galaxies, are stressed. A description is then given of the main numerical techniques of integration of the N-body problem in the framework of stellar dynamics and of the results obtained via N-Body experiments. A final topic is the secular evolution and self-organization of galactic systems.

  4. The Bolocam Galactic Plane Survey

    NASA Technical Reports Server (NTRS)

    Glenn, Jason; Aguirre, James; Bally, John; Battersby, Cara; Bradley, Eric Todd; Cyganowski, Claudia; Dowell, Darren; Drosback, Meredith; Dunham, Miranda K.; Evans, Neal J., II; Ginsburg, Adam; Harvey, Paul; Rosolowsky, Erik; Schlingman, Wayne; Shirley, Yancy L.; Stringfellow, Guy S.; Walawender, Josh; Williams, Jonathan

    2009-01-01

    The Bolocam Galactic Plane Survey (BGPS) is a 1.1 millimeter continuum survey of the northern Galactic Plane made with Bolocam and the Caltech Submillimeter Observatory. The coverage totals 170 square degrees, comprised of a contiguous range from -10.5 deg is less than or equal to 90.5 deg, 0.5 deg is less than or equal to b is less than or equal to 0.5 deg, with extended coverage in b in selected regions, and four targeted regions in the outer Galaxy, including: IC1396, toward the Perseus arm at l is approximately 111 deg, W3/4/5, and Gem OB1. Depths of the maps range from 30 to 60 mJy beam (sup 1). Approximately 8,400 sources were detected and the maps and source catalog have been made publicly available. Millimeter-wave thermal dust emission reveals dense regions within molecular clouds, thus the BGPS serves as a database for studies of the dense interstellar medium and star formation within the Milky Way.

  5. A new galactic chemical evolution model with dust: results for dwarf irregular galaxies and DLA systems

    NASA Astrophysics Data System (ADS)

    Gioannini, L.; Matteucci, F.; Vladilo, G.; Calura, F.

    2016-09-01

    We present a galactic chemical evolution model which adopts updated prescriptions for all the main processes governing the dust cycle. We follow in detail the evolution of the abundances of several chemical species (C, O, S, Si, Fe and Zn) in the gas and dust of a typical dwarf irregular galaxy. The dwarf irregular galaxy is assumed to evolve with a low but continuous level of star formation and experience galactic winds triggered by supernova explosions. We predict the evolution of the gas to dust ratio in such a galaxy and discuss critically the main processes involving dust, such as dust production by AGB stars and Type II SNe, destruction and accretion (gas condensation in clouds). We then apply our model to Damped Lyman-α systems which are believed to be dwarf irregulars, as witnessed by their abundance patterns. Our main conclusions are: i) we can reproduce the observed gas to dust ratio in dwarf galaxies. ii) We find that the process of dust accretion plays a fundamental role in the evolution of dust and in certain cases it becomes the dominant process in the dust cycle. On the other hand, dust destruction seems to be a negligible process in irregulars. iii) Concerning Damped Lyman-α systems, we show that the observed gas-phase abundances of silicon, normalized to volatile elements (zinc and sulfur), are in agreement with our model. iv) The abundances of iron and silicon in DLA systems suggest that the two elements undergo a different history of dust formation and evolution. Our work casts light on the nature of iron-rich dust: the observed depletion pattern of iron is well reproduced only when an additional source of iron dust is considered. Here we explore the possibility of a contribution from Type Ia SNe as well as an efficient accretion of iron nano-particles.

  6. 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.

  7. Seeing red in M32: Constraints on the stellar content from near- and mid-infrared observations and applications for studies of more distant galaxies {sup ,} {sup ,}

    SciTech Connect

    Davidge, T. J.

    2014-08-10

    The properties of asymptotic giant branch (AGB) stars in the Local Group galaxy M32 are investigated using ground- and space-based observations that span the 1-8 μm wavelength interval, with the goal of demonstrating the utility of infrared observations as probes of stellar content. Comparisons with isochrones indicate that the brightest resolved stars in M32 have ages of a few gigayears and are younger on average than AGB stars with the same intrinsic brightness in the outer disk of M31. Accounting for stellar variability is shown to be essential for modeling AGB luminosity functions (LFs). Model LFs that assume the star-forming history measured by Monachesi et al. and the variability properties of Galactic AGB stars match both the K and [5.8] LFs of M32. Models also suggest that the slope of the [5.8] LF between M{sub [5.8]} = –8.5 and –10.0 is sensitive to the mix of stellar ages, and a sizeable fraction of the stars in M32 must have an age older than 7 Gyr in order to match the [5.8] LF. The structural properties of M32 in the infrared are also investigated. The effective radii that are computed from near-infrared and mid-infrared isophotes are similar to those measured at visible wavelengths, suggesting that the stellar content of M32 is well mixed. However, isophotes at radii >16'' (>60 pc) in the near- and mid-infrared are flatter than those at visible wavelengths. The coefficient of the fourth-order cosine term in the Fourier expansion of isophotes changes from 'boxy' values at r < 16'' to 'disky' values at r > 48''in [3.6] and [4.5]. The mid-infrared colors near the center of M32 do not vary systematically with radius, providing evidence of a well mixed stellar content in this part of the galaxy.

  8. Observações espectroscópicas da candidata a pós-AGB IRAS 19386+0155

    NASA Astrophysics Data System (ADS)

    Lorenz-Martins, S.; Pereira, C. B.

    2003-08-01

    Nesse trabalho apresentamos a análise fotosférica da estrela candidata a pós-AGB IRAS 19386+0155. Com os dados obtidos no espectrógrafo FEROS foram determinados os parâmetros atmosféricos e abundâncias fotosféricas utilizando o código MOOG. A análise do espectro mostrou que IRAS 19386+0155 possui os seguintes parâmetros atmosféricos : Teff = 6800K, log g = 1.4, [M/H] = -1.5 e Vt = 8.4 km/s. O padrão de abundância obtido para os elementos mais leves (Carbono, Nitrogênio e Oxigênio) e elementos a (Magnésio, Silício e Cálcio) foi inferior ao solar (log C = 7.74, log N = 7.28, Log O = 8.43, log Mg = 7.14, log Si = 7.54 e log Ca = 5.91). Uma inspeção visual do espectro ISO deste objeto revela a presença de poeira fria na forma de silicatos cristalinos. Embora as bandas mais marcantes de silicatos amorfos (em 10 mm e 18mm) não sejam observadas, a emissão em 21 mm, presente em algumas pós-AGBs também não está presente. O espectro ISO parece revelar um meio rico em oxigênio, mas a forma da distribuição de energia no infravermelho não obedece ao padrão apresentado por outras pós-AGBs. Nossos resultados nos levam a sugerir que IRAS 19386+0155 talvez faça parte de um sistema binário, uma vez que outras pós-AGBs que são membros de sistemas binários apresentam padrão de abundância semelhante.

  9. A CATALOG OF GALACTIC INFRARED CARBON STARS

    SciTech Connect

    Chen, P. S.

    2012-02-15

    We collected almost all of the Galactic infrared carbon stars (IRCSs) from literature published up to the present to organize a catalog of 974 Galactic IRCSs in this paper. Some of their photometric properties in the near-, mid-, and far-infrared are discussed.

  10. Seeing Red

    NASA Technical Reports Server (NTRS)

    2008-01-01

    This New Horizons image of Jupiter's volcanic moon Io was taken at 13:05 Universal Time during the spacecraft's Jupiter flyby on February 28, 2007. It shows the reddish color of the deposits from the giant volcanic eruption at the volcano Tvashtar, near the top of the sunlit crescent, as well as the bluish plume itself and the orange glow of the hot lava at its source. The relatively unprocessed image on the left provides the best view of the volcanic glow and the plume deposits, while the version on the right has been brightened to show the much fainter plume, and the Jupiter-lit night side of Io.

    New Horizons' color imaging of Io's sunlit side was generally overexposed because the spacecraft's color camera, the super-sensitive Multispectral Visible Imaging Camera (MVIC), was designed for the much dimmer illumination at Pluto. However, two of MVIC's four color filters, the blue and 'methane' filter (a special filter designed to map methane frost on the surface of Pluto at an infrared wavelength of 0.89 microns), are less sensitive than the others, and thus obtained some well-exposed views of the surface when illumination conditions were favorable. Because only two color filters are used, rather than the usual three, and because one filter uses infrared light, the color is only a rough approximation to what the human eye would see.

    The red color of the Tvashtar plume fallout is typical of Io's largest volcanic plumes, including the previous eruption of Tvashtar seen by the Galileo and Cassini spacecraft in 2000, and the long-lived Pele plume on the opposite side of Io. The color likely results from the creation of reddish three-atom and four-atom sulfur molecules (S3 and S4) from plume gases rich in two-atom sulfur molecules (S2 After a few months or years, the S3 and S4 molecules recombine into the more stable and familiar yellowish form of sulfur consisting of eight-atom molecules (S8), so these red deposits are only seen around recently-active Io

  11. Spectroscopic Determination of Masses (and Implied Ages) for Red Giants

    NASA Astrophysics Data System (ADS)

    Ness, M.; Hogg, David W.; Rix, H.-W.; Martig, M.; Pinsonneault, Marc H.; Ho, A. Y. Q.

    2016-06-01

    The mass of a star is arguably its most fundamental parameter. For red giant stars, tracers luminous enough to be observed across the Galaxy, mass implies a stellar evolution age. It has proven to be extremely difficult to infer ages and masses directly from red giant spectra using existing methods. From the Kepler and apogee surveys, samples of several thousand stars exist with high-quality spectra and asteroseismic masses. Here we show that from these data we can build a data-driven spectral model using The Cannon, which can determine stellar masses to ˜0.07 dex from apogee dr12 spectra of red giants; these imply age estimates accurate to ˜0.2 dex (40%). We show that The Cannon constrains these ages foremost from spectral regions with CN absorption lines, elements whose surface abundances reflect mass-dependent dredge-up. We deliver an unprecedented catalog of 70,000 giants (including 20,000 red clump stars) with mass and age estimates, spanning the entire disk (from the Galactic center to R˜ 20 kpc). We show that the age information in the spectra is not simply a corollary of the birth-material abundances {{[Fe/H]}} and [α /{Fe}], and that, even within a monoabundance population of stars, there are age variations that vary sensibly with Galactic position. Such stellar age constraints across the Milky Way open up new avenues in Galactic archeology.

  12. 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.

  13. MASS OUTFLOW AND CHROMOSPHERIC ACTIVITY OF RED GIANT STARS IN GLOBULAR CLUSTERS. II. M13 AND M92

    SciTech Connect

    Meszaros, Sz.; Dupree, A. K.; Szalai, T. E-mail: dupree@cfa.harvard.edu

    2009-05-15

    High-resolution spectra of 123 red giant stars in the globular cluster M13 and 64 red giant stars in M92 were obtained with Hectochelle at the MMT telescope. Emission and line asymmetries in H{alpha} and Ca II K are identified, characterizing motions in the extended atmospheres and seeking differences attributable to metallicity in these clusters and M15. On the red giant branch, emission in H{alpha} generally appears in stars with T {sub eff} {approx}< 4500 K and log L/L {sub sun}{approx}> 2.75. Fainter stars showing emission are asymptotic giant branch (AGB) stars or perhaps binary stars. The line-bisector for H{alpha} reveals the onset of chromospheric expansion in stars more luminous than log (L/L {sub sun}) {approx} 2.5 in all clusters, and this outflow velocity increases with stellar luminosity. However, the coolest giants in the metal-rich M13 show greatly reduced outflow in H{alpha} most probably due to decreased T {sub eff} and changing atmospheric structure. The Ca II K{sub 3} outflow velocities are larger than shown by H{alpha} at the same luminosity and signal accelerating outflows in the chromospheres. Stars clearly on the AGB show faster chromospheric outflows in H{alpha} than RGB objects. While the H{alpha} velocities on the RGB are similar for all metallicities, the AGB stars in the metal-poor M15 and M92 have higher outflow velocities than in the metal-rich M13. Comparison of these chromospheric line profiles in the paired metal-poor clusters, M15 and M92, shows remarkable similarities in the presence of emission and dynamical signatures, and does not reveal a source of the 'second-parameter' effect.

  14. THE SAGITTARIUS STREAMS IN THE SOUTHERN GALACTIC HEMISPHERE

    SciTech Connect

    Koposov, Sergey E.; Belokurov, V.; Evans, N. W.; Gilmore, G.; Gieles, M.; Irwin, M. J.; Lewis, G. F.; Niederste-Ostholt, M.; Penarrubia, J.; Smith, M. C.; Bizyaev, D.; Malanushenko, E.; Malanushenko, V.; Schneider, D. P.; Wyse, R. F. G.

    2012-05-01

    The structure of the Sagittarius stream in the southern Galactic hemisphere is analyzed with the Sloan Digital Sky Survey Data Release 8. Parallel to the Sagittarius tidal track, but {approx}10 Degree-Sign away, there is another fainter and more metal-poor stream. We provide evidence that the two streams follow similar distance gradients but have distinct morphological properties and stellar populations. The brighter stream is broader, contains more metal-rich stars, and has a richer color-magnitude diagram with multiple turnoffs and a prominent red clump as compared to the fainter stream. Based on the structural properties and the stellar population mix, the stream configuration is similar to the Northern 'bifurcation'. In the region of the South Galactic Cap, there is overlapping tidal debris from the Cetus stream, which crosses the Sagittarius stream. Using both photometric and spectroscopic data, we show that the blue straggler population belongs mainly to Sagittarius and the blue horizontal branch stars belong mainly to the Cetus stream in this confused location in the halo.

  15. Exploring the vertical age structure of the Galactic disc

    NASA Astrophysics Data System (ADS)

    Casagrande, Luca

    While in external or high-redshift galaxies we can only measure integrated stellar properties at best, the Milky Way offers us the unique opportunity to study its individual baryonic components, including stars. We use oscillations measured in red giant stars by the Kepler satellite to derive stellar ages and explore the vertical age structure across few kpc of the Milky Way disc. We find that old stars dominate at increasing Galactic heights, whereas closer to the plane a rich zoology of ages exists. The age distribution of stars shows a smooth distribution over the last 10 Gyr, which together with a flat age-metallicity relation is consistent with a quiescent evolution for the Milky Way disc since a redshift of about two.

  16. Emission-line objects projected upon the galactic bulge.

    PubMed

    Herbig, G H

    1969-08-01

    Low-dispersion slit spectrograms have been obtained of 34 faint objects that lie in the direction of the galactic bulge and have the Halpha line in emission upon a detectable continuum. Eleven of these are certain or probable symbiotic stars. A rough comparison with R CrB stars in the same area suggests that these brightest symbiotics in the bulge have in the mean M(v) approximately -3 to -4, which suggest Population II red giants rather than conventional Population I M-type objects. The sample also contains a number of hot stars having H and [O II] or [O III] in emission, as well as four conventional Be stars, and six certain or possible planetary nebulae. PMID:16578699

  17. Galactic Center Fly-in

    NASA Astrophysics Data System (ADS)

    Hanson, A.; Fu, C.-W.; Li, Y.; Frisch, P. C.

    2006-06-01

    Beginning with the familiar constellations of the night sky, we present a multispectral zoom into the core of the Milky Way Galaxy. After traveling over seven orders of magnitude in spatial scale, we discover the violent phenomena occurring within one light year of the Black Hole at the Galactic Core. This animated zoom includes data with wavelengths from radio to X-ray, and is based entirely on data or models that have been aligned at all spatial scales in order to provide a single continuous visual trip into the Center of the Milky Way Galaxy. The visualization challenge has been to align and choreograph data acquired over a wide range of wavelength and spatial scales, and obtain a new scientific as well as educational perspective of the dense core of our Galaxy.

  18. Theory of active galactic nuclei

    NASA Technical Reports Server (NTRS)

    Shields, G. A.

    1986-01-01

    The involvement of accretion disks around supermassive black holes in the theory of active galactic nuclei (AGN) is discussed. The physics of thin and thick accretion disks is discussed and the partition between thermal and nonthermal energy production in supermassive disks is seen as uncertain. The thermal limit cycle may operate in supermassive disks (Shields, 1985), with accumulation of gas in the disk for periods of 10 to the 4th to 10 to the 7th years, punctuated by briefer outbursts during which the mass is rapidly transferred to smaller radii. An extended X-ray source in AGN is consistent with observations (Tennant and Mushotsky, 1983), and a large wind mass loss rate exceeding the central accretion rate means that only a fraction of the mass entering the disk will reach the central object; the rest being lost to the wind. Controversy in the relationship between the broad lines and the disk is also discussed.

  19. Star formation across galactic environments

    NASA Astrophysics Data System (ADS)

    Young, Jason

    I present here parallel investigations of star formation in typical and extreme galaxies. The typical galaxies are selected to be free of active galactic nuclei (AGN), while the extreme galaxies host quasars (the most luminous class of AGN). These two environments are each insightful in their own way; quasars are among the most violent objects in the universe, literally reshaping their host galaxies, while my sample of AGN-free star-forming galaxies ranges from systems larger than the Milky Way to small galaxies which are forming stars at unsustainably high rates. The current paradigm of galaxy formation and evolution suggests that extreme circumstances are key stepping stones in the assembly of galaxies like our Milky Way. To test this paradigm and fully explore its ramifications, this dual approach is needed. My sample of AGN-free galaxies is drawn from the KPNO International Spectroscopic Survey. This Halpha-selected, volume-limited survey was designed to detect star-forming galaxies without a bias toward continuum luminosity. This type of selection ensures that this sample is not biased toward galaxies that are large or nearby. My work studies the KISS galaxies in the mid- and far-infrared using photometry from the IRAC and MIPS instruments aboard the Spitzer Space Telescope. These infrared bands are particularly interesting for star formation studies because the ultraviolet light from young stars is reprocessed into thermal emission in the far-infrared (24mum MIPS) by dust and into vibrational transitions features in the mid-infrared (8.0mum IRAC) by polycyclic aromatic hydrocarbons (PAHs). The work I present here examines the efficiencies of PAH and thermal dust emission as tracers of star-formation rates over a wide range of galactic stellar masses. I find that the efficiency of PAH as a star-formation tracer varies with galactic stellar mass, while thermal dust has a highly variable efficiency that does not systematically depend on galactic stellar mass

  20. The galactic model of GRBs

    SciTech Connect

    Colgate, S.A.; Li, H.

    1997-09-01

    The galactic model of gamma ray bursts (GRBs) is based upon the observed production of soft gamma ray repeaters (SGRs) in the galaxy and the consequences of a reasonable model to explain them. In this view GRBs are the long term result of the burn-out conditions of the SGRs in this and in other galaxies. A delay of {approximately} 30 million years before GRBs are being actively produced can be understood as the time required for the ejected matter during the SGR phase to cool, condense, and form planetesimals that are eventually captured by the central neutron star. The amount of disk matter and the interaction between each GRB and the disk determine the rate of burst production and turn-off time of GRBs. The x-ray afterglow as well as optical emission is derived from x-ray fluorescence and ionization of previously ablated matter.

  1. The Physical Nature of the Circum-Galactic Medium

    NASA Astrophysics Data System (ADS)

    Faucher-Giguere, Claude-Andre

    The installation of the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST) as part of its last servicing mission has revolutionized the study of gas in and around galaxies through the study of ultra-violet (UV) diagnostics. These diagnostics are enabling studies of gas flows in and out of low-redshift, evolved galaxies that are not feasible from the ground. Despite the great observational advances made possible with COS, it is necessary to complement the high-quality spectra with theoretical modeling sufficiently accurate for robust and complete physical interpretation so that the full scientific potential of the mission can be realized. The clear correlation between O VI absorption in galactic halos and the specific star formation rate of central galaxies revealed by COS, in particular, highlights the close connection between circum-galactic gas and galaxies. It is now also appreciated that the gaseous halos of galaxies contain a total mass and a mass in metals that are at least comparable to (and likely significantly greater than) the total and metal masses in the interstellar medium of galaxies. The circum-galactic medium (CGM) is thus intimately related to galaxy evolution, including the transformation of blue star-forming disks into red passive ellipticals. However, the physical origin of observed galaxy-halo gas correlations and of halo gas in general is presently not understood. We will model the CGM of low-redshift galaxies probed by HST observations with cosmological simulations of unprecedented resolution and with much more physically predictive models of star formation and stellar and black hole feedback than previously available. Our simulations will also employ a numerical solver that resolves all the main historical differences between grid- and particle-based hydrodynamical codes. Importantly, we will process all of our simulations with radiative transfer calculations to faithfully map the simulations to observable quantities, a

  2. Dust formation in the oxygen-rich AGB star IK Tauri

    NASA Astrophysics Data System (ADS)

    Gobrecht, D.; Cherchneff, I.; Sarangi, A.; Plane, J. M. C.; Bromley, S. T.

    2016-01-01

    interferometric observations. The derived dust-to-gas mass ratio for IK Tau is in the range 1-6 × 10-3 and agrees with values derived from observations of O-rich Mira-type stars. Conclusions: Our results confirm the importance of periodic shocks in chemically shaping the inner wind of AGB stars and providing gas conditions conducive to the efficient synthesis of molecules and dust by non-equilibrium processes. They indicate that the wind acceleration will possibly develop in the radius range 4-8 R⋆ in IK Tau.

  3. The Nature of the lithium rich giants. Mixing episodes on the RGB and early-AGB

    NASA Astrophysics Data System (ADS)

    Charbonnel, C.; Balachandran, S. C.

    2000-07-01

    We present a critical analysis of the nature of the so-called Li-rich RGB stars. For a majority of the stars, we have used Hipparcos parallaxes to determine masses and evolutionary states by comparing their position on the Hertzsprung-Russell diagram with theoretical evolutionary tracks. Among the twenty Li-rich giants whose location on the HR diagram we were able to determine precisely, five appear to be Li-rich because they have not completed the standard first dredge-up dilution, and three have abundances compatible with the maximum allowed by standard dilution. Thus, these should be re-classified as Li-normal. For the remaining stars, the high Li abundance must be a result of fresh synthesis of this fragile element. We identify two distinct episodes of Li production which occur in advanced evolutionary phases depending upon the mass of the star. Low-mass RGB stars, which later undergo the helium flash, produce Li at the phase referred to as the bump in the luminosity function. At this evolutionary phase, the outwardly-moving hydrogen shell burns through the mean molecular weight discontinuity created by the first dredge-up. Any extra-mixing process can now easily connect the 3He-rich envelope material to the outer regions of the hydrogen-burning shell, enabling Li production by the Cameron & Fowler (1971) process. While very high Li abundances are then reached, this Li-rich phase is extremely short lived because once the mixing extends deep enough to lower the carbon isotopic ratio below the standard dilution value, the freshly synthesized Li is quickly destroyed. In intermediate-mass stars, the mean molecular weight gradient due to the first dredge-up is not erased until after the star has begun to burn helium in its core. The Li-rich phase in these stars occurs when the convective envelope deepens at the base of the AGB, permitting extra-mixing to play an effective role. Li production ceases when a strong mean molecular weight gradient is built up between the

  4. MIPS Infrared Imaging of AGB Dustshells (MIRIAD): tracing mass-loss histories in the extremely large shells around evolved stars

    NASA Astrophysics Data System (ADS)

    Speck, Angela; Elitzur, Moshe; Gehrz, Robert; Herwig, Falk; Izumiura, Hideyuki; Latter, William; Matsuura, Mikako; Meixner, Margaret; Steffen, Matthias; Stencel, Robert; Szczerba, Ryszard; Ueta, Toshiya; Zijlstra, Albert

    2005-06-01

    Evolved intermediate mass stars are major contributors to the interstellar medium. However, the mechanisms by which they do this are not well understood. The circumstellar shells of evolved stars (AGB and post-AGB stars) contain the fossil record of their mass loss, and therefore have the potential to verify many aspects of stellar evolution. IRAS and ISO data indicate that huge dust shells exist around many such objects, extending several parsecs from the central star. Furthermore, these large dust shells show evidence for mass-loss variations that correlate with evolutionary changes in the star itself. Previous observations lacked the sensitivity and spatial resolution to investigate the full extent and detailed structure of these large dust shells. Using Spitzer/MIPS's unique sensitivity and mapping capabilities, we propose to produce far-IR images of the parsec-sized dust shells around four carefully selected evolved stars in order to determine the distribution of material in these circumstellar envelopes. These maps will be the deepest yet (sensitivity 1MJy/sr) and have the most complete spatial coverage to date. Crucially, mapping in this level of detail will allow us to: (a) constrain the masses of the progenitor stars; (b) test theories of stellar evolution and mass-loss mechanisms; (c) determine the effect of dust chemistry on mass loss (and therefore on stellar evolution); (d) determine when the aspherical structures so prevalent in planetary nebulae actually develop and thus constrain the cause.

  5. 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.

  6. VizieR Online Data Catalog: Water maser emission toward post-AGB and PN (Gomez+, 2015)

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    The observed sources are listed in Table 1. They comprise most of the sources in Ramos-Larios et al. (2009A&A...501.1207R). They are post-AGB stars and PN candidates with the IRAS color criteria of Suarez et al. (2006A&A...458..173S) and with signs of strong optical obscuration. We have also included some optically visible post-AGB stars from Suarez et al. (2006A&A...458..173S) that were not included in our previous water maser observations of Suarez et al. (2007A&A...467.1085S, 2009A&A...505..217S) or for which those observations had poor sensitivity. We observed the 616-523 transition of H2O (rest frequency = 22235.08MHz) using three different telescopes: the DSS-63 antenna (70m diameter) at the Madrid Deep Space Communications Complex (MDSCC) near Robledo de Chavela (Spain), the 64m antenna at the Parkes Observatory of the Australia Telescope National Facility (ATNF), and the 100m Robert C. Byrd Green Bank Telescope (GBT) of the National Radio Astronomy Observatory. The observed positions, rms noise per spectral channel, and observing dates are listed in Table 1. (3 data files).

  7. The Galactic evolution of phosphorus

    NASA Astrophysics Data System (ADS)

    Caffau, E.; Bonifacio, P.; Faraggiana, R.; Steffen, M.

    2011-08-01

    Context. As a galaxy evolves, its chemical composition changes and the abundance ratios of different elements are powerful probes of the underlying evolutionary processes. Phosphorous is an element whose evolution has remained quite elusive until now, because it is difficult to detect in cool stars. The infrared weak P i lines of the multiplet 1, at 1050-1082 nm, are the most reliable indicators of the presence of phosphorus. The availability of CRIRES at VLT has permitted access to this wavelength range in stellar spectra. Aims: We attempt to measure the phosphorus abundance of twenty cool stars in the Galactic disk. Methods: The spectra are analysed with one-dimensional model-atmospheres computed in local thermodynamic equilibrium (LTE). The line formation computations are performed assuming LTE. Results: The ratio of phosphorus to iron behaves similarly to sulphur, increasing towards lower metallicity stars. Its ratio with respect to sulphur is roughly constant and slightly larger than solar, [P/S] = 0.10 ± 0.10. Conclusions: We succeed in taking an important step towards the understanding of the chemical evolution of phosphorus in the Galaxy. However, the observed rise in the P/Fe abundance ratio is steeper than predicted by Galactic chemical evolution model developed by Kobayashi and collaborators. Phosphorus appears to evolve differently from the light odd-Z elements sodium and aluminium. The constant value of [P/S] with metallicity implies that P production is insensitive to the neutron excess, thus processes other than neutron captures operate. We suggest that proton captures on 30Si and α captures on 27Al are possibilities to investigate. We see no clear distinction between our results for stars with planets and stars without any detected planet. Based on observations obtained with the CRIRES spectrograph at ESO-VLT Antu 8.2 m telescope at Paranal, Programme 386.D-0130, P.I. E. Caffau.

  8. Star Formation Across Galactic Environments

    NASA Astrophysics Data System (ADS)

    Young, Jason

    2013-01-01

    I present here parallel investigations of star formation in AGN-free and quasar host galaxies. These environments are both insightful; quasars are among the most violent objects known, reshaping their host galaxies, while my sample of AGN-free star-forming galaxies ranges from systems larger than the Milky Way to dwarf star-forming galaxies. The AGN-free galaxies are drawn from the KPNO International Spectroscopic Survey, an Hα-selected, volume-limited survey was designed to avoid continuum luminosity bias. This work studies the KISS galaxies in mid- and far-IR using Spitzer IRAC and MIPS photometry. These IR bands are interesting because the UV light from young stars is reprocessed into thermal emission in the far-IR (24μm MIPS) by dust and into vibrational transition features in the mid-IR (8.0μm IRAC) by polycyclic aromatic hydrocarbons (PAHs). This work examines the efficiencies of PAH and dust emission as tracers of star-formation. I find that the efficiency of PAH as a star-formation tracer varies with galactic stellar mass, while thermal dust has no systematic dependance on galactic mass. My study of quasar host galaxies utilizes images of eight PG quasars from the WFPC2 and NICMOS instruments aboard HST. I use narrow-band images centered on the Hβ, [OII]λ3727, [OIII]λ5007, and Paα emission lines to construct extinction and star formation maps. Additionally, I use line-ratio maps to distinguish AGN-powered line emission from star formation powered line emission. I find star formation, albeit at rates are lower than expected, suggesting that quasar host galaxies are dynamically more advanced than suspected. Seven of the galaxies have higher mass-specific star-formation rates. Additionally, I see evidence of shocked gas, supporting the hypotheses from earlier works that AGN activity quenches star formation in host galaxies by disrupting gas reservoirs.

  9. Microlensing by the galactic bar

    NASA Technical Reports Server (NTRS)

    Zhao, Hongsheng; Spergel, David N.; Rich, R. Michael

    1995-01-01

    We compute the optical depth and duration distribution of microlensing events towrd Baade's window in a model composed of a Galactic disk and a bar. The bar model is a self-consistent dynamical model built out of individual orbits that has been populated to be consistent with the COBE maps of the Galaxy and kinematic observations of the Galactic bulge. We find that most of the lenses are in the bulge with a line-of-sight distance 6.25 kpc (adopting R(sub 0) = 8 kpc). The microlensing optical depth of a 2 x 10(exp 10) solar mass bar plus a truncated disk is (2.2 +/- 0.45) x 10(exp -6), consistent with the large optical depth (3.2 +/- 1.2) x 10(exp -6) found by Udalski et al. (1994). This model optical depth is enhanced over the predictions of axisymmetric models by Kiraga & Paczynski (1994) by slightly more than a factor of 2, since the bar is elongated along the line of sight. The large Einstein radius and small transverse velocity dispersion also predict a longer event duration in the self-consistent bar model than in the Kiraga-Paczynski model. The event rate and duration distribution also depend on the lower mass cutoff of the lens mass function. With a 0.1 solar mass cutoff, five to seven events (depending on the contribution of disk lenses) with a logarithmic mean duration of 20 days are expected for the Optical Gravitational Lensing Experiment (OGLE) according to our model, while Udalski et al. (1994) observed nine events with durations from 8 to 62 days. On the other hand, if most of the lenses are brown dwarfs, our model predicts too many short-duration events. A Kolmogorov-Smirnov test finds only 7% probability for the model with 0.01 solar mass cutoff to be consistent with current data.

  10. PREFACE: Galactic Center Workshop 2006

    NASA Astrophysics Data System (ADS)

    Schödel, Rainer; Bower, Geoffrey C.; Muno, Michael P.; Nayakshin, Sergei; Ott, Thomas

    2006-12-01

    We are pleased to present the proceedings from the Galactic Center Workshop 2006—From the Center of the Milky Way to Nearby Low-Luminosity Galactic Nuclei. The conference took place in the Physikzentrum, Bad Honnef, Germany, on 18 to 22 April 2006. It is the third workshop of this kind, following the Galactic Center Workshops held 1998 in Tucson, Arizona, and 2002 in Kona, Hawaii. The center of the Milky Way is the only galactic nucleus of a fairly common spiral galaxy that can be observed in great detail. With a distance of roughly 8 kpc, the resolution that can currently be achieved is of the order 40 mpc/8000 AU in the X-ray domain, 2 mpc/400 AU in the near-infrared, and 0.01 mpc/1 AU with VLBI in the millimeter domain. This is two to three orders of magnitude better than for any comparable nearby galaxy, making thus the center of the Milky Way thetemplate object for the general physical interpretation of the phenomena that can be observed in galactic nuclei. We recommend the summary article News from the year 2006 Galactic Centre workshopby Mark Morris and Sergei Nayakshin—who also gave the summary talk of the conference—to the reader in order to obtain a first, concise overview of the results presented at the workshop and some of the currently most exciting—and debated—developments in recent GC research. While the workshops held in 1998 and 2002 were dedicated solely to the center of the Milky Way, the field of view was widened in Bad Honnef to include nearby low-luminosity nuclei. This new feature followed the realization that not only the GC serves as a template for understanding extragalactic nuclei, but that the latter can also provide the context and broader statistical base for understanding the center of our Milky Way. This concerns especially the accretion and emission processes related to the Sagittarius A*, the manifestation of the super massive black hole in the GC, but also the surprising observation of great numbers of massive, young

  11. Clouds Dominate the Galactic Halo

    NASA Astrophysics Data System (ADS)

    2003-01-01

    Using the exquisite sensitivity of the National Science Foundation's Robert C. Byrd Green Bank Telescope (GBT), astronomer Jay Lockman of the National Radio Astronomy Observatory (NRAO) in Green Bank, W. Va., has produced the best cross-section ever of the Milky Way Galaxy's diffuse halo of hydrogen gas. This image confirms the presence of discrete hydrogen clouds in the halo, and could help astronomers understand the origin and evolution of the rarefied atmosphere that surrounds our Galaxy. Lockman presented his findings at the American Astronomical Society meeting in Seattle, WA. Hydrogen Clouds Graphic Artist's Rendering of the Milky Way (background) with insert showing GBT image of cross-section of neutral atomic Hydrogen Credit: Kirk Woellert/National Science Foundation Patricia Smiley, NRAO. "The first observations with the Green Bank Telescope suggested that the hydrogen in the lower halo, the transition zone between the Milky Way and intergalactic space, is very clumpy," said Lockman. "The latest data confirm these results and show that instead of trailing away smoothly from the Galactic plane, a significant fraction of the hydrogen gas in the halo is concentrated in discrete clouds. There are even some filaments." Beyond the star-filled disk of the Milky Way, there exists an extensive yet diffuse halo of hydrogen gas. For years, astronomers have speculated about the origin and structure of this gas. "Even the existence of neutral hydrogen in the halo has been somewhat of a puzzle," Lockman remarked. "Unlike the Earth's atmosphere, which is hot enough to hold itself up against the force of gravity, the hydrogen in the halo is too cool to support itself against the gravitational pull of the Milky Way." Lockman points out that some additional factor has to be involved to get neutral hydrogen to such large distances from the Galactic plane. "This force could be cosmic rays, a supersonic wind, the blast waves from supernovae, or something we have not thought of

  12. PREFACE: Galactic Center Workshop 2006

    NASA Astrophysics Data System (ADS)

    Schödel, Rainer; Bower, Geoffrey C.; Muno, Michael P.; Nayakshin, Sergei; Ott, Thomas

    2006-12-01

    We are pleased to present the proceedings from the Galactic Center Workshop 2006—From the Center of the Milky Way to Nearby Low-Luminosity Galactic Nuclei. The conference took place in the Physikzentrum, Bad Honnef, Germany, on 18 to 22 April 2006. It is the third workshop of this kind, following the Galactic Center Workshops held 1998 in Tucson, Arizona, and 2002 in Kona, Hawaii. The center of the Milky Way is the only galactic nucleus of a fairly common spiral galaxy that can be observed in great detail. With a distance of roughly 8 kpc, the resolution that can currently be achieved is of the order 40 mpc/8000 AU in the X-ray domain, 2 mpc/400 AU in the near-infrared, and 0.01 mpc/1 AU with VLBI in the millimeter domain. This is two to three orders of magnitude better than for any comparable nearby galaxy, making thus the center of the Milky Way thetemplate object for the general physical interpretation of the phenomena that can be observed in galactic nuclei. We recommend the summary article News from the year 2006 Galactic Centre workshopby Mark Morris and Sergei Nayakshin—who also gave the summary talk of the conference—to the reader in order to obtain a first, concise overview of the results presented at the workshop and some of the currently most exciting—and debated—developments in recent GC research. While the workshops held in 1998 and 2002 were dedicated solely to the center of the Milky Way, the field of view was widened in Bad Honnef to include nearby low-luminosity nuclei. This new feature followed the realization that not only the GC serves as a template for understanding extragalactic nuclei, but that the latter can also provide the context and broader statistical base for understanding the center of our Milky Way. This concerns especially the accretion and emission processes related to the Sagittarius A*, the manifestation of the super massive black hole in the GC, but also the surprising observation of great numbers of massive, young

  13. A study of galactic light, extragalactic light, and galactic structure using Pioneer 10 observations of background starlight

    NASA Astrophysics Data System (ADS)

    Toller, G. N.

    The diffuse astronomical background sky brightness (background starlight) was determined over 95 percent of the sky using Pioneer 10 photometric measurements in sky regions where the zodiacal light is negligible. Brightness levels are presented at blue (3950-4850A) and red (5900-6800A) wavelengths. The B-R color index distribution is established over the celestial sphere. A computer model of our galaxy was constructed which computes the emitted and observed brightness from any volume element. The relation between DGL, direct starlight, and extinction along the line of sight is established. A small influence of galactic spiral structure on surface brightness levels exists at 1 = 2 deg (Sagittarius arm), 1 = 69 deg (Orion arm), and 1 = 288 deg (Carina arm). A correlation between brightness features and interstellar extinction is established. Analysis of the distribution of brightness peaks and dips and the location of the brightness symmetry plane establishes the Sun's elevation above the galactic plane as 12.2 + or - 2.1 pc.

  14. Galactic Bulge Giants: Probing Stellar and Galactic Evolution. 1. Catalogue of Spitzer IRAC and MIPS Sources (PREPRINT)

    NASA Technical Reports Server (NTRS)

    Uttenthaler, Stefan; Stute, Matthias; Sahai, Raghvendra; Blommaert, Joris A.; Schultheis, Mathias; Kraemer, Kathleen E.; Groenewegen, Martin A.; Price, Stephan D.

    2010-01-01

    Aims. We aim at measuring mass-loss rates and the luminosities of a statistically large sample of Galactic bulge stars at several galactocentric radii. The sensitivity of previous infrared surveys of the bulge has been rather limited, thus fundamental questions for late stellar evolution, such as the stage at which substantial mass-loss begins on the red giant branch and its dependence on fundamental stellar properties, remain unanswered. We aim at providing evidence and answers to these questions. Methods. To this end, we observed seven 15 15 arcmin2 fields in the nuclear bulge and its vicinity with unprecedented sensitivity using the IRAC and MIPS imaging instruments on-board the Spitzer Space Telescope. In each of the fields, tens of thousands of point sources were detected. Results. In the first paper based on this data set, we present the observations, data reduction, the final catalogue of sources, and a detailed comparison to previous mid-IR surveys of the Galactic bulge, as well as to theoretical isochrones. We find in general good agreement with other surveys and the isochrones, supporting the high quality of our catalogue.

  15. DIFFUSE GALACTIC LIGHT IN THE FIELD OF THE TRANSLUCENT HIGH GALACTIC LATITUDE CLOUD MBM32

    SciTech Connect

    Ienaka, N.; Kawara, K.; Matsuoka, Y.; Oyabu, S.; Sameshima, H.; Tsujimoto, T.; Peterson, B. A.

    2013-04-10

    We have conducted B-, g-, V-, and R-band imaging in a 45' Multiplication-Sign 40' field containing part of the high Galactic latitude translucent cloud MBM32, and correlated the intensity of diffuse optical light S{sub {nu}}({lambda}) with that of 100 {mu}m emission S{sub {nu}}(100 {mu}m). A {chi}{sup 2} minimum analysis is applied to fit a linear function to the measured correlation and derive the slope parameter b({lambda}) = {Delta}S{sub {nu}}({lambda})/{Delta}S{sub {nu}}(100 {mu}m) of the best-fit linear function. Compiling a sample by combining our b({lambda}) and published ones, we show that the b({lambda}) strength varies from cloud to cloud by a factor of four. Finding that b({lambda}) decreases as S{sub {nu}}(100 {mu}m) increases in the sample, we suggest that a nonlinear correlation including a quadratic term of S{sub {nu}}(100 {mu}m){sup 2} should be fitted to the measured correlation. The variation of optical depth, which is A{sub V} = 0.16-2.0 in the sample, can change b({lambda}) by a factor of 2-3. There would be some contribution to the large b({lambda}) variation from the forward-scattering characteristic of dust grains which is coupled to the non-isotropic interstellar radiation field (ISRF). Models of the scattering of diffuse Galactic light (DGL) underestimate the b({lambda}) values by a factor of two. This could be reconciled by deficiency in UV photons in the ISRF or by a moderate increase in dust albedo. Our b({lambda}) spectrum favors a contribution from extended red emission (ERE) to the diffuse optical light; b({lambda}) rises from B to V faster than the models, seems to peak around 6000 A and decreases toward long wavelengths. Such a characteristic is expected from the models in which the DGL is combined with ERE.

  16. A New Survey for Red Supergiants in the Magellanic Clouds

    NASA Astrophysics Data System (ADS)

    González-Fernández, C.; Negueruela, I.; Dorda, R.

    2016-10-01

    We present a pilot program focused on the red supergiant population of the Magellanic Clouds, with the intent of extending the current known sample to include the unexplored low end of the brightness distribution of these stars, building a more representative dataset with which to extrapolate their behavior to other Galactic and extra-galactic environments. For a pool of candidates selected over near-infrared photometry, we obtain medium resolution multi-object spectroscopy to confirm their nature and their membership in the clouds. Around two hundred new red supergiants have been detected, hinting at a yet-to-be-observed large population. Based on this sample, new a priori classification criteria are investigated, combining mid- and near-infrared photometry to improve the observational efficiency of programs similar to this. A more complete and detailed analysis of this dataset can be found in González- Fernández et al. (2015).

  17. How to Spot a Disrupted Galactic Satellite

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-03-01

    orbit and is currently at its furthest distance from the Galactic center. They suggest that the elliptic orbit and advanced age of the clump indicate it is most likely to be a disrupted globular cluster, rather than a dwarf galaxy.Interestingly, when the authors went back to search for a stellar overdensity corresponding to Lamost 1 in photometric data, they were unable to detect it. This reaffirms that their approach of searching for velocity and metallicity clumping is an important tool for discovering otherwise-invisible diffuse streams.BonusCheck out this cool graphic Vickers made using Stellarium and Aladin to demonstratewhere in the sky the stars ofLamost 1 are located. Lamost 1sstars are the red dots in the constellation Draco.CitationJohn J. Vickers et al 2016 ApJ 816 L2. doi:10.3847/2041-8205/816/1/L2

  18. Production of Lithium in the Galactic Disk

    NASA Astrophysics Data System (ADS)

    Casuso, E.; Beckman, J. E.

    2000-07-01

    +disk) of abundances of 12C, 13C, 14N, 16O, 26Fe, the two main peaks (one in the halo and one in the disk) in the G-dwarf stellar frequency distribution, and the evolution of 9Be and 10B+11B via GCR spallation reactions without requiring the very high local cosmic-ray fluxes implied by the spallation close to SN. Adding a natural mechanism of differential depletion in red supergiant envelopes, we can explain the observed time evolution of the abundance of D and that of the isotopic ratios 7Li/6Li and 11B/10B starting from a standard big bang nucleosynthesis model with baryon density ~0.05. Our model also predicts the second Li ``plateau'' found for [Fe/H] between -0.2 and +0.2, due to the ``loop back'' implied for Li (also for 9Be and B) because of the required infall of low-metallicity gas to the disk. Without ruling out other mechanisms for the main production of Li in the Galactic disk, the low-energy α+α fusion reaction in the interstellar medium offers a promising contribution.

  19. The nature of the red disc-like galaxies at high redshift: dust attenuation and intrinsically red stellar populations

    NASA Astrophysics Data System (ADS)

    Pierini, D.; Maraston, C.; Gordon, K. D.; Witt, A. N.

    2005-10-01

    We investigate which conditions of dust attenuation and stellar populations allow models of dusty, continuously star-forming, bulge-less disc galaxies at 0.8 <~z<~ 3.2 to meet the different colour selection criteria of high-z`red' galaxies (e.g. RC-K > 5.3, IC-K > 4, J-K > 2.3). As a main novelty, we use stellar population models that include the thermally pulsating asymptotic giant branch (TP-AGB) phase of stellar evolution. The star formation rate of the models declines exponentially as a function of time, the e-folding time being longer than 3 Gyr. In addition, we use calculations of radiative transfer of the stellar and scattered radiation through different dusty interstellar media in order to explore the wide parameter space of dust attenuation. We find that synthetic discs can exhibit red optical/near-infrared colours because of reddening by dust, but only if they have been forming stars for at least ~1 Gyr. Extremely few models barely exhibit RC-K > 5.3, if the inclination i= 90° and if the opacity 2 ×τV>~ 6. Hence, RC-K-selected galaxies at 1 <~z<~ 2 most probably are either systems with an old, passively evolving bulge or starbursts. Synthetic discs at 1 <~z<~ 2 exhibit 4 < IC-K < 4.8, if they are seen edge on (i.e. at i~ 90°) and if 2 ×τV>~ 0.5. This explains the large fraction of observed, edge-on disc-like galaxies with Ks < 19.5 and F814W-Ks>~ 4. Finally, models with 2 <~z<~ 3.2 exhibit 2.3 < J-K < 3, with no bias towards i~ 90° and for a large range in opacity (e.g. 2 ×τV > 1 for i~ 70°). In conclusion, red disc-like galaxies at 0.8 <~z<~ 3.2 may not necessarily be dustier than nearby disc galaxies (with 0.5 <~ 2 ×τV<~ 2) and/or much older than ~1 Gyr. This result is due both to a realistic description of dust attenuation and to the emission contribution by TP-AGB stars, with ages of 0.2 to 1-2 Gyr and intrinsically red colours.

  20. HEAVY ELEMENT NUCLEOSYNTHESIS IN THE BRIGHTEST GALACTIC ASYMPTOTIC GIANT BRANCH STARS

    SciTech Connect

    Karakas, Amanda I.; Garcia-Hernandez, D. A.

    2012-05-20

    We present updated calculations of stellar evolutionary sequences and detailed nucleosynthesis predictions for the brightest asymptotic giant branch (AGB) stars in the Galaxy with masses between 5 M{sub Sun} and 9 M{sub Sun }, with an initial metallicity of Z = 0.02 ([Fe/H] = 0.14). In our previous studies we used the Vassiliadis and Wood mass-loss rate, which stays low until the pulsation period reaches 500 days after which point a superwind begins. Vassiliadis and Wood noted that for stars over 2.5 M{sub Sun} the superwind should be delayed until P Almost-Equal-To 750 days at 5 M{sub Sun }. We calculate evolutionary sequences where we delay the onset of the superwind to pulsation periods of P Almost-Equal-To 700-800 days in models of M = 5, 6, and 7 M{sub Sun }. Post-processing nucleosynthesis calculations show that the 6 and 7 M{sub Sun} models produce the most Rb, with [Rb/Fe] Almost-Equal-To 1 dex, close to the average of most of the Galactic Rb-rich stars ([Rb/Fe] Almost-Equal-To 1.4 {+-} 0.8 dex). Changing the rate of the {sup 22}Ne +{alpha} reactions results in variations of [Rb/Fe] as large as 0.5 dex in models with a delayed superwind. The largest enrichment in heavy elements is found for models that adopt the NACRE rate of the {sup 22}Ne({alpha}, n){sup 25}Mg reaction. Using this rate allows us to best match the composition of most of the Rb-rich stars. A synthetic evolution algorithm is then used to remove the remaining envelope resulting in final [Rb/Fe] of Almost-Equal-To 1.4 dex although with C/O ratios >1. We conclude that delaying the superwind may account for the large Rb overabundances observed in the brightest metal-rich AGB stars.

  1. The Galactic Center Seen Through the Precise, Multiplexed Eye of JWST

    NASA Astrophysics Data System (ADS)

    Lu, Jessica R.

    2013-01-01

    The Galactic center harbors the closest supermassive black hole and contains warm, turbulent molecular clouds, dense stellar populations, and some of the most active star forming regions in the Milky Way. These unique conditions make the Galactic Center a compelling target for understanding how star formation varies with environment, how nuclear star clusters in galaxies evolve, and how supermassive black holes influence their surroundings. Detailed studies of the Galactic center have previously been conducted with ground-based telescopes equipped with adaptive optics in pencil-beam studies. However, Galactic center studies can be dramatically expanded with JWST's combination of large fields-of-view (FOV) and high spatial resolution in the infrared. Of particular relevance for the Galactic Center are NIRCam's suite of narrow-band imaging filters and NIRSpec's IFU spectrograph. The narrow-band imaging should provide precise astrometry, rough spectral types, and emission line maps for ~50,000 stars within a 2' x 2' FOV, while follow up IFU spectroscopy will give precise types and radial velocities for the most interesting subsets of stars. Potential results include: (1) counting the intermediate age red and yellow supergiants that will give information about the recent star formation history; (2) measuring the initial mass function below 1 Msun and studying young stellar objects in known and new young star clusters; (3) using 3D dynamics to model the kinematic evolution of the entire nuclear cluster, find hypervelocity stars, and trace the orbits of gas features and clusters in the region. Galactic Center observations with JWST will give us a more complete picture of the gas, stars, black hole, and their interactions in this dynamic region.

  2. Formation of Circumstellar Dust Around an Oxygen-Rich AGB Star W Hya: AlO and SiO Observations with ALMA

    NASA Astrophysics Data System (ADS)

    Takigawa, A.; Kamizuka, T.; Tachibana, S.; Yamamura, I.

    2016-08-01

    In order to understand the formation of circumstellar dust and the origin of presolar grains, we observed spatial distributions of AlO and SiO molecules around an oxygen-rich AGB star, W Hya, with ALMA (cycle 3).

  3. H II REGION DRIVEN GALACTIC BUBBLES AND THEIR RELATIONSHIP TO THE GALACTIC MAGNETIC FIELD

    SciTech Connect

    Pavel, Michael D.; Clemens, D. P. E-mail: clemens@bu.edu

    2012-12-01

    The relative alignments of mid-infrared traced Galactic bubbles are compared to the orientation of the mean Galactic magnetic field in the disk. The orientations of bubbles in the northern Galactic plane were measured and are consistent with random orientations-no preferential alignment with respect to the Galactic disk was found. A subsample of H II region driven Galactic bubbles was identified, and as a single population they show random orientations. When this subsample was further divided into subthermal and suprathermal H II regions, based on hydrogen radio recombination linewidths, the subthermal H II regions showed a marginal deviation from random orientations, but the suprathermal H II regions showed significant alignment with the Galactic plane. The mean orientation of the Galactic disk magnetic field was characterized using new near-infrared starlight polarimetry and the suprathermal H II regions were found to preferentially align with the disk magnetic field. If suprathermal linewidths are associated with younger H II regions, then the evolution of young H II regions is significantly affected by the Galactic magnetic field. As H II regions age, they cease to be strongly linked to the Galactic magnetic field, as surrounding density variations come to dominate their morphological evolution. From the new observations, the ratios of magnetic-to-ram pressures in the expanding ionization fronts were estimated for younger H II regions.

  4. The Heliosphere and the Galactic Environment

    NASA Video Gallery

    The boundaries surrounding our heliosphere can change both due to changes in our galactic environment and through changes in the solar wind emitted by the Sun. We see here an animation of the bound...

  5. Evaluation of Galactic Cosmic Ray Models

    NASA Technical Reports Server (NTRS)

    Adams, James H., Jr.; Heiblim, Samuel; Malott, Christopher

    2009-01-01

    Models of the galactic cosmic ray spectra have been tested by comparing their predictions to an evaluated database containing more than 380 measured cosmic ray spectra extending from 1960 to the present.

  6. Dark matter particles in the galactic halo

    SciTech Connect

    Bernabei, R. Belli, P.; Montecchia, F.; Nozzoli, F.; Cappella, F.; D'Angelo, A.; Incicchitti, A.; Prosperi, D.; Cerulli, R.; Dai, C. J.; He, H. L.; Kuang, H. H.; Ma, J. M.; Sheng, X. D.; Ye, Z. P.

    2009-12-15

    Arguments on the investigation of the DarkMatter particles in the galactic halo are addressed. Recent results obtained by exploiting the annual modulation signature are summarized and the perspectives are discussed.

  7. Dark matter particles in the galactic halo

    NASA Astrophysics Data System (ADS)

    Bernabei, R.; Belli, P.; Montecchia, F.; Nozzoli, F.; Cappella, F.; D'Angelo, A.; Incicchitti, A.; Prosperi, D.; Cerulli, R.; Dai, C. J.; He, H. L.; Kuang, H. H.; Ma, J. M.; Sheng, X. D.; Ye, Z. P.

    2009-12-01

    Arguments on the investigation of the DarkMatter particles in the galactic halo are addressed. Recent results obtained by exploiting the annual modulation signature are summarized and the perspectives are discussed.

  8. The galactic globular cluster system

    NASA Technical Reports Server (NTRS)

    Djorgovski, S.; Meylan, G.

    1994-01-01

    We explore correlations between various properties of Galactic globular clusters, using a database on 143 objects. Our goal is identify correlations and trends which can be used to test and constrain theoretical models of cluster formation and evolution. We use a set of 13 cluster parameters, 9 of which are independently measured. Several arguments suggest that the number of clusters still missing in the obscured regions of the Galaxy is of the order of 10, and thus the selection effects are probably not severe for our sample. Known clusters follow a power-law density distribution with a slope approximately -3.5 to -4, and an apparent core with a core radius approximately 1 kpc. Clusters show a large dynamical range in many of their properties, more so for the core parameters (which are presumably more affected by dynamical evolution) than for the half-light parameters. There are no good correlations with luminosity, although more luminous clusters tend to be more concentrated. When data are binned in luminosity, several trends emerge: more luminous clusters tend to have smaller and denser cores. We interpret this as a differential survival effect, with more massive clusters surviving longer and reaching more evolved dynamical states. Cluster core parameters and concentrations also correlate with the position in the Galaxy, with clusters closer to the Galactic center or plane being more concentrated and having smaller and denser cores. These trends are more pronounced for the fainter (less massive) clusters. This is in agreement with a picture where tidal shocks form disk or bulge passages accelerate dynamical evolution of clusters. Cluster metallicities do not correlate with any other parameter, including luminosity and velocity dispersion; the only detectable trend is with the position in the Galaxy, probably reflecting Zinn's disk-halo dichotomy. This suggests that globular clusters were not self-enriched systems. Velocity dispersions show excellent correlations

  9. Relativistic Dark Matter at the Galactic Center

    SciTech Connect

    Amin, Mustafa A.; Wizansky, Tommer; /SLAC

    2007-11-16

    In a large region of the supersymmetry parameter space, the annihilation cross section for neutralino dark matter is strongly dependent on the relative velocity of the incoming particles. We explore the consequences of this velocity dependence in the context of indirect detection of dark matter from the galactic center. We find that the increase in the annihilation cross section at high velocities leads to a flattening of the halo density profile near the galactic center and an enhancement of the annihilation signal.

  10. A Galactic Binary Detection Pipeline

    NASA Technical Reports Server (NTRS)

    Littenberg, Tyson B.

    2011-01-01

    The Galaxy is suspected to contain hundreds of millions of binary white dwarf systems, a large fraction of which will have sufficiently small orbital period to emit gravitational radiation in band for space-based gravitational wave detectors such as the Laser Interferometer Space Antenna (LISA). LISA's main science goal is the detection of cosmological events (supermassive black hole mergers, etc.) however the gravitational signal from the galaxy will be the dominant contribution to the data - including instrumental noise over approximately two decades in frequency. The catalogue of detectable binary systems will serve as an unparalleled means of studying the Galaxy. Furthermore, to maximize the scientific return from the mission, the data must be "cleansed" of the galactic foreground. We will present an algorithm that can accurately resolve and subtract 2:: 10000 of these sources from simulated data supplied by the Mock LISA Data Challenge Task Force. Using the time evolution of the gravitational wave frequency, we will reconstruct the position of the recovered binaries and show how LISA will sample the entire compact binary population in the Galaxy.

  11. WIMPs at the galactic center

    SciTech Connect

    Agrawal, Prateek; Batell, Brian; Fox, Patrick J.; Harnik, Roni

    2015-05-07

    Simple models of weakly interacting massive particles (WIMPs) predict dark matter annihilations into pairs of electroweak gauge bosons, Higgses or tops, which through their subsequent cascade decays produce a spectrum of gamma rays. Intriguingly, an excess in gamma rays coming from near the Galactic center has been consistently observed in Fermi data. A recent analysis by the Fermi collaboration confirms these earlier results. Taking into account the systematic uncertainties in the modelling of the gamma ray backgrounds, we show for the first time that this excess can be well fit by these final states. In particular, for annihilations to (WW, ZZ, hh, tt{sup -bar}), dark matter with mass between threshold and approximately (165, 190, 280, 310) GeV gives an acceptable fit. The fit range for bb{sup -bar} is also enlarged to 35 GeV≲m{sub χ}≲165 GeV. These are to be compared to previous fits that concluded only much lighter dark matter annihilating into b, τ, and light quark final states could describe the excess. We demonstrate that simple, well-motivated models of WIMP dark matter including a thermal-relic neutralino of the MSSM, Higgs portal models, as well as other simplified models can explain the excess.

  12. Radioactivity in the galactic plane

    NASA Technical Reports Server (NTRS)

    Walraven, G. D.; Haymes, R. C.

    1976-01-01

    The paper reports the detection of a large concentration of interstellar radioactivity during balloon-altitude measurements of gamma-ray energy spectra in the band between 0.02 and 12.27 MeV from galactic and extragalactic sources. Enhanced counting rates were observed in three directions towards the plane of the Galaxy; a power-law energy spectrum is computed for one of these directions (designated B 10). A large statistical deviation from the power law in a 1.0-FWHM interval centered near 1.16 MeV is discussed, and the existence of a nuclear gamma-ray line at 1.15 MeV in B 10 is postulated. It is suggested that Ca-44, which emits gamma radiation at 1.156 MeV following the decay of radioactive Sc-44, is a likely candidate for this line, noting that Sc-44 arises from Ti-44 according to explosive models of supernova nucleosynthesis. The 1.16-MeV line flux inferred from the present data is shown to equal the predicted flux for a supernova at a distance of approximately 3 kpc and an age not exceeding about 100 years.

  13. WIMPs at the galactic center

    SciTech Connect

    Agrawal, Prateek; Batell, Brian; Fox, Patrick J.; Harnik, Roni

    2015-05-07

    Simple models of weakly interacting massive particles (WIMPs) predict dark matter annihilations into pairs of electroweak gauge bosons, Higgses or tops, which through their subsequent cascade decays produce a spectrum of gamma rays. Intriguingly, an excess in gamma rays coming from near the Galactic center has been consistently observed in Fermi data. A recent analysis by the Fermi collaboration confirms these earlier results. Taking into account the systematic uncertainties in the modelling of the gamma ray backgrounds, we show for the first time that this excess can be well fit by these final states. In particular, for annihilations to (WW, ZZ, hh, tt¯), dark matter with mass between threshold and approximately (165, 190, 280, 310) GeV gives an acceptable fit. The fit range for bb¯ is also enlarged to 35 GeV ≲ mχ ≲ 165 GeV. These are to be compared to previous fits that concluded only much lighter dark matter annihilating into b, τ, and light quark final states could describe the excess. We demonstrate that simple, well-motivated models of WIMP dark matter including a thermal-relic neutralino of the MSSM, Higgs portal models, as well as other simplified models can explain the excess.

  14. WIMPs at the galactic center

    DOE PAGESBeta

    Agrawal, Prateek; Batell, Brian; Fox, Patrick J.; Harnik, Roni

    2015-05-07

    Simple models of weakly interacting massive particles (WIMPs) predict dark matter annihilations into pairs of electroweak gauge bosons, Higgses or tops, which through their subsequent cascade decays produce a spectrum of gamma rays. Intriguingly, an excess in gamma rays coming from near the Galactic center has been consistently observed in Fermi data. A recent analysis by the Fermi collaboration confirms these earlier results. Taking into account the systematic uncertainties in the modelling of the gamma ray backgrounds, we show for the first time that this excess can be well fit by these final states. In particular, for annihilations to (WW,more » ZZ, hh, tt¯), dark matter with mass between threshold and approximately (165, 190, 280, 310) GeV gives an acceptable fit. The fit range for bb¯ is also enlarged to 35 GeV ≲ mχ ≲ 165 GeV. These are to be compared to previous fits that concluded only much lighter dark matter annihilating into b, τ, and light quark final states could describe the excess. We demonstrate that simple, well-motivated models of WIMP dark matter including a thermal-relic neutralino of the MSSM, Higgs portal models, as well as other simplified models can explain the excess.« less

  15. WIMPs at the galactic center

    SciTech Connect

    Agrawal, Prateek; Fox, Patrick J.; Harnik, Roni; Batell, Brian E-mail: brian.batell@cern.ch E-mail: roni@fnal.gov

    2015-05-01

    Simple models of weakly interacting massive particles (WIMPs) predict dark matter annihilations into pairs of electroweak gauge bosons, Higgses or tops, which through their subsequent cascade decays produce a spectrum of gamma rays. Intriguingly, an excess in gamma rays coming from near the Galactic center has been consistently observed in Fermi data. A recent analysis by the Fermi collaboration confirms these earlier results. Taking into account the systematic uncertainties in the modelling of the gamma ray backgrounds, we show for the first time that this excess can be well fit by these final states. In particular, for annihilations to (WW, ZZ, hh, t t-bar ), dark matter with mass between threshold and approximately (165, 190, 280, 310) GeV gives an acceptable fit. The fit range for b b-bar is also enlarged to 35 GeV ∼< m{sub χ} ∼< 165 GeV. These are to be compared to previous fits that concluded only much lighter dark matter annihilating into b, τ, and light quark final states could describe the excess. We demonstrate that simple, well-motivated models of WIMP dark matter including a thermal-relic neutralino of the MSSM, Higgs portal models, as well as other simplified models can explain the excess.

  16. Assessing Performance of P-Band Backscattering Coefficients and TSAR in Hemi-Boreal Forest AGB Estimation

    NASA Astrophysics Data System (ADS)

    Li, Wenmei; Chen, Erxue; Li, Zengyuan; Feng, Qi

    2014-11-01

    To assess performance of P-band backscattering coefficients and TSAR for hemi-boreal forest AGB estimation, airborne P-band repeat-path Pol-InSAR data collected by ESAR in Ramingstorp test site during March and May 2007 are applied. The correlation coefficient (R) between P-band backscattering coefficients and in-situ biomass reaches 0.87 for HH polarization. Meanwhile, the R between P-band backscattering power at specific height and in-situ biomass are higher in VV polarization than that in HH and HV polarization. And R between P-band backscattering power and in-situ biomass reaches 0.70 at 5m and 10m height in VV polarization.

  17. VizieR Online Data Catalog: LMC post-AGB, post-RGB star and YSOs (Kamath+, 2015)

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    To obtain an initial sample selection for our spectroscopic survey, we adopted the sample selected by van Aarle et al. (2011A&A...530A..90V, Cat. J/A+A/530/A90), who identified optically visible post-AGB star candidates in the LMC based on photometry. We obtained low-resolution spectra of stars selected from the initial sample of objects. The spectra were taken using the AAOmega double-beam multi-fibre spectrograph mounted on the 3.9m Anglo Australian Telescope (AAT) at Siding Spring Observatory (SSO). AAOmega allows for the simultaneous observation of 392 targets (including science objects, sky-positions, and fiducial guide stars) over a 2 degree field using the 2dF fibre positioner. (11 data files).

  18. 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}⊙ , 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}⊙ . 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.

  19. ARCADE 2 Observations of Galactic Radio Emission

    NASA Technical Reports Server (NTRS)

    Kogut, A.; Fixsen, D. J.; Levin, S. M.; Limon, M.; Lubin, P. M.; Mirel, P.; Seiffert, M.; Singal, J.; Villela, T.; Wollack, E.; Wuensche, C. A.

    2010-01-01

    We use absolutely calibrated data from the Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission (ARCADE 2) flight in July 2006 to model Galactic emission at frequencies 3, 8, and 10 GHz. The spatial structure in the data is consistent with a superposition of free-free and synchrotron emission. Emission with spatial morphology traced by the Haslam 408 MHz survey has spectral index beta_synch = -2.5 +/- 0.1, with free-free emission contributing 0.10 +/- 0.01 of the total Galactic plane emission in the lowest ARCADE 2 band at 3.15 GHz. We estimate the total Galactic emission toward the polar caps using either a simple plane-parallel model with csc|b| dependence or a model of high-latitude radio emission traced by the COBE/FIRAS map of CII emission. Both methods are consistent with a single power-law over the frequency range 22 MHz to 10 GHz, with total Galactic emission towards the north polar cap T_Gal = 0.498 +/- 0.028 K and spectral index beta = -2.55 +/- 0.03 at reference frequency 0.31 GHz. The well calibrated ARCADE 2 maps provide a new test for spinning dust emission, based on the integrated intensity of emission from the Galactic plane instead of cross-correlations with the thermal dust spatial morphology. The Galactic plane intensity measured by ARCADE 2 is fainter than predicted by models without spinning dust, and is consistent with spinning dust contributing 0.4 +/- 0.1 of the Galactic plane emission at 23 GHz.

  20. Masses for Galactic Beat Cepheids

    NASA Astrophysics Data System (ADS)

    D'Cruz, Noella L.; Morgan, Siobahn M.; Böhm-Vitense, Erika

    2000-08-01

    Accurate mass determinations for Cepheids may be used to determine the degree of excess mixing in the interiors of their main-sequence progenitors: the larger the excess mixing, the larger the luminosity of the Cepheid of a given mass, or the smaller the mass of a Cepheid with given luminosity. Dynamical masses determined recently for a few Cepheid binaries indicate excess mixing somewhat stronger than that corresponding to the convective overshoot models by Schaller et al. Beat Cepheids can be used similarly to test main-sequence mixing in stellar interiors. The period ratios for beat Cepheids depend on luminosity, Teff, heavy element abundance, and mass. By comparing pulsational models and the observationally derived luminosity, Teff, metallicities, and period ratios it is possible to obtain masses for these stars, the so-called beat masses. With the old opacities masses much smaller than the evolutionary masses were obtained. With the new OPAL opacities a beat mass close to the dynamical mass was obtained for the binary beat Cepheid Y Carinae, showing that it is now possible to obtain reliable beat masses. In this paper, we determine beat masses for seven Galactic beat Cepheids for which photometric and spectroscopic data are available. We find an average mass around 4.2+/-0.3 Msolar for these stars, though the actual error limits for each star may be larger mainly because of uncertainties in E(B-V) and the heavy element abundances. (As derived spectroscopically, beat Cepheids are in general metal-poor, with -0.4<~[Fe/H]<~0.0). The relation between the derived beat masses and the luminosities again indicates excess mixing that is somewhat larger than that corresponding to the models by Schaller et al.

  1. Galactic Globular Cluster Relative Ages

    NASA Astrophysics Data System (ADS)

    De Angeli, Francesca; Piotto, Giampaolo; Cassisi, Santi; Busso, Giorgia; Recio-Blanco, Alejandra; Salaris, Maurizio; Aparicio, Antonio; Rosenberg, Alfred

    2005-07-01

    We present accurate relative ages for a sample of 55 Galactic globular clusters. The ages have been obtained by measuring the difference between the horizontal branch and the turnoff in two internally photometrically homogeneous databases. The mutual consistency of the two data sets has been assessed by comparing the ages of 16 globular clusters in common between the two databases. We have also investigated the consistency of our relative age determination within the recent stellar model framework. All clusters with [Fe/H]<-1.7 are found to be old and coeval, with the possible exception of two objects, which are marginally younger. The age dispersion for the metal-poor clusters is 0.6 Gyr (rms), consistent with a null age dispersion. Intermediate-metallicity clusters (-1.7<[Fe/H]<-0.8) are on average 1.5 Gyr younger than the metal-poor ones, with an age dispersion of 1.0 Gyr (rms) and a total age range of ~3 Gyr. About 15% of the intermediate-metallicity clusters are coeval with the oldest clusters. All the clusters with [Fe/H]>-0.8 are ~1 Gyr younger than the most metal-poor ones, with a relatively small age dispersion, although the metal-rich sample is still too small to allow firmer conclusions. There is no correlation of the cluster age with the galactocentric distance. We briefly discuss the implication of these observational results for the formation history of the Galaxy. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555, and on observations made at the European Southern Observatory, La Silla, Chile, and with the Isaac Newton Group Telescopes.

  2. Reinforcing the link between the double red clump and the X-shaped bulge of the Milky Way

    NASA Astrophysics Data System (ADS)

    Gonzalez, O. A.; Zoccali, M.; Debattista, V. P.; Alonso-García, J.; Valenti, E.; Minniti, D.

    2015-11-01

    The finding of a double red clump in the luminosity function of the Milky Way bulge has been interpreted as evidence for an X-shaped structure. Recently, an alternative explanation has been suggested, where the double red clump is an effect of multiple stellar populations in a classical spheroid. In this Letter we provide an observational assessment of this scenario and show that it is not consistent with the behaviour of the red clump across different lines of sight, particularly at high distances from the Galactic plane. Instead, we confirm that the shape of the red clump magnitude distribution closely follows the distance distribution expected for an X-shaped bulge at critical Galactic latitudes. We also emphasize some key observational properties of the bulge red clump that should not be neglected in the search for alternative scenarios. Based on observations taken within the ESO VISTA Public Survey VVV, Programme ID 179.B-2002.

  3. On the atmospheric structure and fundamental parameters of red supergiants

    NASA Astrophysics Data System (ADS)

    Wittkowski, M.; Arroyo-Torres, B.; Marcaide, J. M.; Abellan, F. J.; Chiavassa, A.; Freytag, B.; Scholz, M.; Wood, P. R.; Hauschildt, P. H.

    2015-01-01

    We present near-infrared spectro-interferometric studies of red supergiant (RSG) stars using the VLTI/AMBER instrument, which are compared to previously obtained similar observations of AGB stars. Our observations indicate spatially extended atmospheric molecular layers of water vapor and CO, similar as previously observed for Mira stars. Data of VY~CMa indicate that the molecular layers are asymmetric, possibly clumpy. Thanks to the spectro-interferometric capabilities of the VLTI/AMBER instrument, we can isolate continuum bandpasses, estimate fundamental parameters of our sources, locate them in the HR diagram, and compare their positions to recent evolutionary tracks. For the example of VY CMa, this puts it close to evolutionary tracks of initial mass 25-32 M ⊙. Comparisons of our data to hydrostatic model atmospheres, 3d simulations of convection, and 1d dynamic model atmospheres based on self-excited pulsation models indicate that none of these models can presently explain the observed atmospheric extensions for RSGs. The mechanism that levitates the atmospheres of red supergiant is thus a currently unsolved problem.

  4. HUBBLE'S SEARCH FOR FAINT FIELD STARS IN GALACTIC HALO

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Left A NASA Hubble Space Telescope image of a randomly selected area of sky taken to search for faint red stars that might constitute dark matter in our Milky Way Galaxy. (Dark matter is material of an unknown type that makes up most of the mass of our galaxy). If the dark matter in our Galaxy was made of faint red stars -- as many scientists have previously conjectured -- then about 38 such stars should have been visible in this HST image. The simulated stars (diamond-shaped symbols), based on theoretical calculations, illustrate what scientists would have seen if the dark matter were locked-up in faint red stars. These surprising results rule out dim stars as an explanation for dark matter in our Galaxy. Right The unmodified HST image shows the region is actually so devoid of stars that far more distant background galaxies can easily be seen. The field is in the constellation Eridanus, far outside the plane of our Milky Way Galaxy. This region was chosen to highlight stars in the galactic halo, where dark matter exists, and to avoid the contribution of faint stars in the plane of the Galaxy. Technical Information: The image was constructed from seven exposures totaling almost three hours of searching by HST. The field shown is about 1.5 arc-minutes across. The image was taken in near-infrared light (814 nm) with the Wide Field Planetary Camera 2, on Feb 8, 1994. This observation is part of the HST parallel observing program. Credit: J Bahcall, Institute for Advance Study, Princeton and NASA

  5. Galaxies as Standard Crayons: Measuring Galactic Reddening with Background Passive Galaxies

    NASA Astrophysics Data System (ADS)

    Goldston Peek, Joshua; Graves, G. J.

    2010-01-01

    To determine the true colors of extra-Galactic sources, we require an accurate map of the extinction generated by the foreground dust in the Milky Way. The Sloan Digital Sky Survey (SDSS), among many others, relies on the maps provided by Schlegel, Finkbeiner and Davis (1998; SFD98). These are derived from maps of infrared dust emission and dust temperature, based on the assumption that dust absorption can be uniquely determined from its infrared emission properties.  We check these maps using the colors of passively evolving galaxies from the SDSS. Passive galaxies populate a tight, well-defined 'red sequence' in the color-magnitude diagram.  This sequence can be used as a 'standard crayon': an object of known true color.  We search for deviations in the colors of red sequence galaxies as a function of position on the SDSS sky, taking into account small systematic variations with redshift and local galaxy environment. We present a corrected map of Galactic reddening, with very significant differences from SFD98. These maps will be made available to the public to use for more precise Galactic reddening. We also compare our reddening results to an alternative method, using neutral hydrogen (HI) column as a proxy for galactic reddening. We employ new HI maps from GALFA-HI, which has comparable resolution to the SFD98 maps. Additionally, we use the standard crayon method to put constraints on the presence of cold dust in high-velocity clouds, which have been shown to lack dust emission but whose reddening properties have not been accurately measured.

  6. RED-LETTER DAYS

    EPA Science Inventory

    The word "red-letter" is an adjective meaning "of special significance." It's origin is from the practice of marking Christian holy days in red letters on calendars. The "red-letter days" to which I refer occurred while I was a graduate student of ...

  7. Red blood cell production

    MedlinePlus

    ... cells are an important element of blood. Their job is to transport oxygen to the body’s tissues in exchange for carbon dioxide, which is carried to and eliminated by the lungs. Red blood cells are formed in the red bone marrow of bones. Stem cells in the red bone marrow called hemocytoblasts ...

  8. Further ALMA observations and detailed modeling of the Red Rectangle

    NASA Astrophysics Data System (ADS)

    Bujarrabal, V.; Castro-Carrizo, A.; Alcolea, J.; Santander-García, M.; van Winckel, H.; Sánchez Contreras, C.

    2016-09-01

    Aims: We aim to study the rotating and expanding gas in the Red Rectangle, which is a well known bipolar nebula surrounding a double stellar system whose primary is a post-asymptotic giant branch (post-AGB) star. We analyze the properties of both components and the relation between them. Rotating disks have been very elusive in post-AGB nebulae, in which gas is almost always found to be in expansion. Methods: We present new high-quality ALMA observations of this source in C17O J = 6-5 and H13CN J = 4-3 line emission and results from a new reduction of already published 13CO J = 3-2 data. A detailed model fitting of all the molecular line data, also discussing previous maps and single-dish observations of lines of CO, CII, and CI, was performed using a sophisticated code that includes an accurate nonlocal treatment of radiative transfer in 2D (assuming axial symmetry). These observations (of low- and high-opacity lines requiring various degrees of excitation) and the corresponding modeling allowed us to deepen the analysis of the nebular properties. We also stress the uncertainties, particularly in the determination of the boundaries of the CO-rich gas and some properties of the outflow. Results: We confirm the presence of a rotating equatorial disk and an outflow, which is mainly formed of gas leaving the disk. The mass of the disk is ~0.01 M⊙, and that of the CO-rich outflow is around ten times smaller. High temperatures of ≳100 K are derived for most components. From comparison of the mass values, we roughly estimate the lifetime of the rotating disk, which is found to be of about 10 000 yr. Taking data of a few other post-AGB composite nebulae into account, we find that the lifetimes of disks around post-AGB stars typically range between about 5000 and more than 20 000 yr. The angular momentum of the disk is found to be high, ~9 M⊙ AU km s-1, which is comparable to that of the stellar system at present. Our observations of H13CN show a particularly wide

  9. KINEMATICAL AND CHEMICAL VERTICAL STRUCTURE OF THE GALACTIC THICK DISK. I. THICK DISK KINEMATICS ,

    SciTech Connect

    Moni Bidin, C.; Carraro, G.; Mendez, R. A.

    2012-03-10

    The variation of the kinematical properties of the Galactic thick disk with Galactic height Z is studied by means of 412 red giants observed in the direction of the south Galactic pole up to 4.5 kpc from the plane. We confirm the non-null mean radial motion toward the Galactic anticenter found by other authors, but we find that it changes sign at |Z| = 3 kpc, and the proposed inward motion of the local standard of rest alone cannot explain these observations. The rotational velocity decreases with |Z| by -30 km s{sup -1} kpc{sup -1}, but the data are better represented by a power law with index 1.25, similar to that proposed from the analysis of Sloan Digital Sky Survey data. All the velocity dispersions increase with |Z|, but the vertical gradients are small. The dispersions grow proportionally, with no significant variation of the anisotropy. The ratio {sigma}{sub U}/{sigma}{sub W} = 2 suggests that the thick disk could have formed from a low-latitude merging event. The vertex deviation increases with Galactic height, reaching {approx}20 Degree-Sign at |Z| = 3.5 kpc. The tilt angle also increases, and the orientation of the ellipsoid in the radial-vertical plane is constantly intermediate between the alignment with the cylindrical and the spherical coordinate systems. The tilt angle at |Z| = 2 kpc coincides with the expectations of MOdified Newtonian Dynamics, but an extension of the calculations to higher |Z| is required to perform a conclusive test. Finally, between 2.5 and 3.5 kpc we detect deviations from the linear trend of many kinematical quantities, suggesting that some kinematical substructure could be present.

  10. Kinematical and Chemical Vertical Structure of the Galactic Thick Disk. I. Thick Disk Kinematics

    NASA Astrophysics Data System (ADS)

    Moni Bidin, C.; Carraro, G.; Méndez, R. A.

    2012-03-01

    The variation of the kinematical properties of the Galactic thick disk with Galactic height Z is studied by means of 412 red giants observed in the direction of the south Galactic pole up to 4.5 kpc from the plane. We confirm the non-null mean radial motion toward the Galactic anticenter found by other authors, but we find that it changes sign at |Z| = 3 kpc, and the proposed inward motion of the local standard of rest alone cannot explain these observations. The rotational velocity decreases with |Z| by -30 km s-1 kpc-1, but the data are better represented by a power law with index 1.25, similar to that proposed from the analysis of Sloan Digital Sky Survey data. All the velocity dispersions increase with |Z|, but the vertical gradients are small. The dispersions grow proportionally, with no significant variation of the anisotropy. The ratio σU/σW = 2 suggests that the thick disk could have formed from a low-latitude merging event. The vertex deviation increases with Galactic height, reaching ~20° at |Z| = 3.5 kpc. The tilt angle also increases, and the orientation of the ellipsoid in the radial-vertical plane is constantly intermediate between the alignment with the cylindrical and the spherical coordinate systems. The tilt angle at |Z| = 2 kpc coincides with the expectations of MOdified Newtonian Dynamics, but an extension of the calculations to higher |Z| is required to perform a conclusive test. Finally, between 2.5 and 3.5 kpc we detect deviations from the linear trend of many kinematical quantities, suggesting that some kinematical substructure could be present. Based on observations collected at the European Organization for Astronomical Research in the Southern Hemisphere, Chile (proposal IDs 075.B-0459(A), 077.B-0348(A)). This paper includes data gathered with the 6.5 m Magellan and the duPont Telescopes, located at Las Campanas Observatory, Chile.

  11. Kinematics of Tycho-2 red giant clump stars

    NASA Astrophysics Data System (ADS)

    Bobylev, V. V.; Stepanishchev, A. S.; Bajkova, A. T.; Gontcharov, G. A.

    2009-12-01

    Based on the Ogorodnikov-Milne model, we analyze the proper motions of 95,633 red giant clump (RGC) stars from the Tycho-2 Catalogue. The following Oort constants have been found: A = 15.9 ± 0.2 km s-1 kpc-1 and B = -12.0±0.2 km s-1 kpc-1. Using 3632 RGC stars with known proper motions, radial velocities, and photometric distances, we show that, apart from the star centroid velocity components relative to the Sun, only the model parameters that describe the stellar motions in the XY plane differ significantly from zero. We have studied the contraction (a negative K effect) of the system of RGC stars as a function of their heliocentric distance and elevation above the Galactic plane. For a sample of distant (500-1000 pc) RGC stars located near the Galactic plane (|z| < 200 pc) with an average distance of d = 0.7 kpc, the contraction velocity is shown to be Kd = -3.5 ±0.9 km s-1; a noticeable vertex deviation, lxy = 9.1° ± 0.5°, is also observed for them. For stars located well above the Galactic plane (|z| ≥200 pc), these effects are less pronounced, Kd = -1.7 ± 0.5 km s-1 and lxy = 4.9° ± 0.6°. Using RGC stars, we have found a rotation around the Galactic X axis directed toward the Galactic center with an angular velocity of -2.5 ± 0.3 km s-1 kpc-1, which we associate with the warp of the Galactic stellar-gaseous disk.

  12. Spectroscopic determination of masses (and implied ages) for red giants

    NASA Astrophysics Data System (ADS)

    Ness, Melissa; Hogg, David W.; Rix, Hans-Walter; Martig, Marie; Ho, Anna

    2016-01-01

    The mass of a star is arguably its most fundamental parameter and for red giant stars it implies a stellar evolution age. Stellar masses and ages have never been derived directly from spectra of red giants. However, using the APOGEE Kepler sample of stars, (the APOKASC sample), with high-quality spectra and astroseismic masses, we can build a data-driven spectral model using THE CANNON (arXiv:1501.07604) to infer stellar mass and therefore age from stellar spectra. We determine stellar masses to 0.07 dex from APOGEE DR12 spectra of red giants; these imply age estimates accurate to 0.2 dex (40 percent). THE CANNON constrains the ages foremost from spectral regions with particular absorption lines, elements whose surface abundances reflect mass-dependent dredge-up. We deliver an unprecedented catalog of 85,000 giants (including 20,000 red-clump stars) with mass and age estimates, spanning the entire disk (from the Galactic center to R ˜ 20 kpc). Such stellar age constraints across the Milky Way open up new avenues in Galactic archeology.

  13. GCN: a gaseous Galactic halo stream?

    NASA Astrophysics Data System (ADS)

    Jin, Shoko

    2010-10-01

    We show that a string of HI clouds that form part of the high-velocity cloud complex known as GCN is a probable gaseous stream extending over more than 50° in the Galactic halo. The radial velocity gradient along the stream is used to deduce transverse velocities as a function of distance, enabling a family of orbits to be computed. We find that a direction of motion towards the Galactic disc coupled with a mid-stream distance of ~20kpc provides a good match to the observed sky positions and radial velocities of the HI clouds comprising the stream. With an estimated mass of 105Msolar, its progenitor is likely to be a dwarf galaxy. However, no stellar counterpart has been found amongst the currently known Galactic dwarf spheroidal galaxies or stellar streams and the exact origin of the stream is therefore currently unknown.

  14. FIRE simulations: galactic outflows and their consequences

    NASA Astrophysics Data System (ADS)

    Keres, Dusan; FIRE team

    2016-06-01

    We study gaseous outflows and their consequences in high-resolution galaxy formation simulations with explicit stellar feedback from the Feedback in Realistic Environments project. Collective, galaxy scale, effect of stellar feedback results in episodic ejections of large amount of gas and heavy elements into the circum-galactic medium. Gas ejection episodes follow strong bursts of star formation. Properties of galactic star formation and ejection episodes depend on galaxy mass and redshift and, together with gas infall and recycling, shape the evolution of the circum-galactic medium and galaxies. As a consequence, our simulated galaxies have masses, star formation histories and heavy element content in good agreement with the observed population of galaxies.

  15. Einstein observations of the galactic centre

    NASA Technical Reports Server (NTRS)

    Watson, M. G.; Willingale, R.; Hertz, P.; Grindlay, J. E.

    1981-01-01

    A description is presented of the X-ray observations made with the Einstein Observatory Imaging Proportional Counter of a 1 x 1 degree field centered near the galactic nucleus. In the direction of the galactic center the interstellar medium is generally opaque to all radiation between the visual and extreme ultraviolet due to the large column density of the intervening gas and dust. The importance of this X-ray study lies in the fact that it opens up a new window in which the central regions of the Milky Way Galaxy can be observed. The X-ray image is clearly dominated by a bright, central region of emission elongated along the galactic plane. Also presented are a number of unresolved sources.

  16. The Galactic Center region imaged by VERITAS

    NASA Astrophysics Data System (ADS)

    Beilicke, M.; VERITAS Collaboration

    2012-11-01

    The Galactic Center has long been a region of interest for high-energy and very-high-energy observations. Many potential sources of GeV/TeV γ-ray emission have been suggested, e.g., the accretion of matter onto the black hole, cosmic rays from a nearby supernova remnant, or the annihilation of dark matter particles. The Galactic Center has been detected at MeV/GeV energies by EGRET and recently by Fermi/LAT. At GeV/TeV energies, the Galactic Center was detected by different ground-based Cherenkov telescopes such as CANGAROO, Whipple 10 m, HESS, and MAGIC. We present the results from 15 h of VERITAS observations conducted at large zenith angles, resulting in a >10 standard deviation detection. The combined Fermi/VERITAS results are compared to astrophysical models.

  17. Nonthermal galactic emission below 10 MHz

    NASA Technical Reports Server (NTRS)

    Novaco, J. C.; Brown, L. W.

    1977-01-01

    The Radio Astronomy Explorer-2 (RAE-2) satellite has provided new measurements of the nonthermal galactic radio emission at frequencies below 10 MHz. Measurements of the emission spectra are presented for the center, anticenter, north polar, and south polar directions at 22 frequencies between 0.25 and 9.18 MHz. Survey maps of the spatial distribution of the observed low frequency galactic emission at 1.31, 2.20, 3.93, 4.70, 6.55, and 9.18 MHz are presented. The observations were obtained with the 229-meter traveling-wave V-antenna on this lunar orbiting spacecraft. The improved frequency coverage offers additional insights into structure of the local galactic neighborhood.

  18. Gamma rays, cosmic rays, and galactic structure

    NASA Technical Reports Server (NTRS)

    Stecker, F. W.

    1977-01-01

    Observations of cosmic and gamma radiation by SAS-2 satellite are summarized and analyzed to determine processes responsible for producing observed galactic radiation. In addition to the production of gamma rays in discrete galactic objects such as pulsars, there are three main mechanisms by which high-energy (greater than 100 MeV) radiation is produced by high-energy interactions involving cosmic rays in interstellar space. These processes, which produce what may be called diffuse galactic gamma-rays, are: (1) the decay of pi mesons produced by interactions of cosmic ray nucleons with interstellar gas nuclei; (2) the bremsstrahlung radiation produced by cosmic ray electrons interacting in the Coulomb fields of nuclei of interstellar gas atoms; and (3) Compton interactions between cosmic ray electrons and low-energy photons in interstellar space.

  19. The distances of the Galactic Novae

    NASA Astrophysics Data System (ADS)

    Ozdonmez, Aykut; Guver, Tolga; Cabrera-Lavers, Antonio; Ak, Tansel

    2016-07-01

    Using location of the RC stars on the CMDs obtained from the UKIDSS, VISTA and 2MASS photometry, we have derived the reddening-distance relations towards each Galactic nova for which at least one independent reddening measurement exists. We were able to determine the distances of 72 Galactic novae and set lower limits on the distances of 45 systems. The reddening curves of the systems are presented. These curves can be also used to estimate reddening or the distance of any source, whose location is close to the position of the nova in our sample. The distance measurement method in our study can be easily applicable to any source, especially for ones that concentrated along the Galactic plane.

  20. SAS-2 gamma-ray results from the galactic plane and their implications for galactic structure and galactic cosmic-ray dynamics

    NASA Technical Reports Server (NTRS)

    Fichtel, C. E.; Kniffen, D. A.; Thompson, D. J.

    1977-01-01

    The final SAS-2 results related to high energy galactic gamma-ray emission show a strong correlation with galactic structural features seen at other wavelenghts, when the known gamma-ray sources are subtracted. Theoretical considerations and analysis of the gamma-ray data suggest that the galactic cosmic rays are dynamically coupled to the interstellar matter through the magnetic fields, and hence the cosmic ray density is enhanced where the matter density is greatest on the scale of the galactic arms. This concept has been explored in a galactic model that assumes: (1) cosmic rays are galactic and not universal; (2)on the scale of the galactic arms, the cosmic ray column (surface) density is proportional to the total interstellar gas column density; (3)the cosmic ray scale height is significantly larger than the scale height to the matter; and (4) ours is a spiral galaxy characterized by an arm to interarm density ratio of over 2:1.

  1. The diffuse galactic far-ultraviolet sky

    SciTech Connect

    Hamden, Erika T.; Schiminovich, David; Seibert, Mark

    2013-12-20

    We present an all-sky map of the diffuse Galactic far ultraviolet (1344-1786 Å) background using Galaxy Evolution Explorer data, covering 65% of the sky with 11.79 arcmin{sup 2} pixels. We investigate the dependence of the background on Galactic coordinates, finding that a standard cosecant model of intensity is not a valid fit. Furthermore, we compare our map to Galactic all-sky maps of 100 μm emission, N {sub H} {sub I} column, and Hα intensity. We measure a consistent low level far-UV (FUV) intensity at zero points for other Galactic quantities, indicating a 300 photons cm{sup –2} s{sup –1} sr{sup –1} Å{sup –1} non-scattered isotropic component to the diffuse FUV. There is also a linear relationship between FUV and 100 μm emission below 100 μm values of 8 MJy sr{sup –1}. We find a similar linear relationship between FUV and N {sub H} {sub I} below 10{sup 21} cm{sup –2}. The relationship between FUV and Hα intensity has no such constant cutoff. For all Galactic quantities, the slope of the linear portion of the relationship decreases with Galactic latitude. A modified cosecant model, taking into account dust scattering asymmetry and albedo, is able to accurately fit the diffuse FUV at latitudes above 20°. The best fit model indicates an albedo, a, of 0.62 ± 0.04 and a scattering asymmetry function, g, of 0.78 ± 0.05. Deviations from the model fit may indicate regions of excess FUV emission from fluorescence or shock fronts, while low latitude regions with depressed FUV emission are likely the result of self-shielding dusty clouds.

  2. Relativity and the Galactic-center stars

    NASA Astrophysics Data System (ADS)

    Saha, Prasenjit; Angélil, R.

    2011-05-01

    Galactic-center stars such as S2 reach speeds of a few percent of light at closest approach to the black hole. Hence relativistic effects are potentially observable. The redshift of a star during pericenter passage is especially sensitive to relativity. The same applies to pulsar timing, if a pulsar in that region is discovered. In this work we explain how the equivalence principle, space curvature and frame dragging in principle reveal themselves through the redshift, and discuss possible strategies for disentangling these from the Newtonian perturbations of other mass in the Galactic-center region.

  3. 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.

  4. Using Spitzer Data To Obtain Dust Distribution Arounfd The Active Galactic Nucleus NGC 4051

    NASA Astrophysics Data System (ADS)

    Pereira, Vincent; Burrell, A.; Chavez, O.; Fawcett, E.; Elias, R.; Lugo, T.; Morillo, E.; Purpura, M.; Sorokin, S.; Gorjian, V.; Adkins, J.; Borders, K.; Kelly, S.; Martin, C.; Mendez, B.; Paradis, J.; Pittman, P.; Sepulveda, B.

    2010-01-01

    We have used the Rees'model of Seyfert I galaxies to make detailed calculations of dust distribution as a function of the slope of the spectral intensity versus frequency curve in the infra-red. From these results and our observations of the active galactic nucleus NGC 4051 with the Spitzer Space Telescope Infrared Array Camera (IRAC) we obtain the dust distribution function for this nucleus. We feel that this research project with its underlying physical concepts serves as a good introduction to the physics of Seyfert galaxies for high school students.

  5. Gamma ray constraints on the Galactic supernova rate

    NASA Technical Reports Server (NTRS)

    Hartmann, D.; The, L.-S.; Clayton, Donald D.; Leising, M.; Mathews, G.; Woosley, S. E.

    1991-01-01

    We perform Monte Carlo simulations of the expected gamma ray signatures of Galactic supernovae of all types to estimate the significance of the lack of a gamma ray signal due to supernovae occurring during the last millenium. Using recent estimates of the nuclear yields, we determine mean Galactic supernova rates consistent with the historic supernova record and the gamma ray limits. Another objective of these calculations of Galactic supernova histories is their application to surveys of diffuse Galactic gamma ray line emission.

  6. 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

  7. 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

  8. SiO masers from AGB stars in the vibrationally excited v = 1, v = 2, and v = 3 states

    NASA Astrophysics Data System (ADS)

    Desmurs, J.-F.; Bujarrabal, V.; Lindqvist, M.; Alcolea, J.; Soria-Ruiz, R.; Bergman, P.

    2014-05-01

    Context. The v = 1 and v = 2 J = 1-0 (43 GHz), and v = 1 J = 2-1 (86 GHz) SiO masers are intense in asymptotic giant branch (AGB) stars and have been mapped using very long baseline interferometry (VLBI) showing ring-like distributions. Those of the v = 1, v = 2 J = 1-0 masers are similar, but the spots are rarely coincident, while the v = 1 J = 2-1 maser arises from a well-separated region farther out. These relative locations can be explained by models tools that include the overlap of two IR lines of SiO and H2O. The v = 3 J = 1-0 line is not directly affected by any line overlap and its spot structure and position, relative to the other lines, is a good test to the standard pumping models. Aims: The aim of this project are to gain insight into the properties and the general theoretical considerations of the different SiO masers that can help to understand them. Methods: We present single-dish and simultaneous VLBI observations of the v = 1, v = 2, and v = 3 J = 1-0 maser transitions of 28SiO in several AGB stars. The results are compared to the predictions of radiative models of SiO masers that both include and not include the effect of IR line overlap. Results: The spatial distribution of the SiO maser emission in the v = 3 J = 1-0 transition from AGB stars is systematically composed of a series of spots that occupy a ring-like structure (as often found in SiO masers). The overall ring structure is extremely similar to that found in the other 43 GHz transitions and is very different from the structure of the v = 1 J = 2-1 maser. The positions of the individual spots of the different 43 GHz lines are, however, very rarely coincident, which in general is separated by about 0.3 AU (between 1 and 5 mas). These results are very difficult to reconcile with standard pumping models, which predict that the masers of rotational transitions within a given vibrational state require very similar excitation conditions (since the levels are placed practically at the same

  9. EVOLUTION, NUCLEOSYNTHESIS, AND YIELDS OF AGB STARS AT DIFFERENT METALLICITIES. III. INTERMEDIATE-MASS MODELS, REVISED LOW-MASS MODELS, AND THE pH-FRUITY INTERFACE

    SciTech Connect

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

    2015-08-15

    We present a new set of models for intermediate-mass asymptotic giant branch (AGB) stars (4.0, 5.0, and 6.0 M{sub ⊙}) at different metallicities (−2.15 ≤ [Fe/H] ≤ +0.15). This set integrates the existing models for low-mass AGB stars (1.3 ≤ M/M{sub ⊙} ≤ 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 {sup 22}Ne(α,n){sup 25}Mg 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)

  10. 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).

  11. Contributions to the Galactic Halo from In-Situ, Kicked-Out, and Accreted Stars

    NASA Astrophysics Data System (ADS)

    Sheffield, Allyson; Johnston, Kathryn V.; Cunha, Katia; Smith, Verne; Majewski, Steven

    2015-08-01

    The chemical and kinematical properties of stars in the Galactic halo provide a means to study the formation history of the Milky Way. Stars formed within a satellite galaxy will bear the imprint of their host dark matter subhalo: star formation is less efficient in less massive protogalactic clumps, so we should observe a specific pattern in [Fe/H] as a function of α-elements and slow/rapid neutron capture elements that reflects this efficiency. Due to their formation in Type II supernovae, α-elements probe the relative timescale of formation for populations of stars. The addition of s- and r-process elements gives a more complete evolutionary picture of the Galaxy. The yields of s- and r-process elements, which are synthesized in Type II supernovae and thermally pulsating AGB stars, respectively, are coupled to the Fe seed nuclei present in the formation site; thus, neutron capture element yields vary with metallicity and provide further constraints on the subhalo’s star formation history.We will report chemical abundances for a sample of 109 M giants in the nearby halo of the Milky Way. The stars were selected for high-resolution spectroscopy based upon their radial velocities: the radial velocities vary significantly from those expected for stars moving on uniform circular orbits in the Galactic disk. Thus, we expect a sample dominated by halo stars. Abundances are derived for α-elements and neutron capture elements. By analyzing the multi-dimensional abundance space, the formation site of the halo giants can be assessed. Of particular interest are a class of stars that form in situ, deep in the Milky Way’s gravitational potential well, but are “kicked out” of the disk into the halo due to a perturbation event. A kicked-out population has recently been identified in Andromeda. N-body simulations predict a range in the percentage of stars belonging to the kicked-out disk population in galaxies. We will present our results within the context of

  12. 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.

  13. MODIFIED GRAVITY SPINS UP GALACTIC HALOS

    SciTech Connect

    Lee, Jounghun; Zhao, Gong-Bo; Li, Baojiu; Koyama, Kazuya

    2013-01-20

    We investigate the effect of modified gravity on the specific angular momentum of galactic halos by analyzing the halo catalogs at z = 0 from high-resolution N-body simulations for a f(R) gravity model that meets the solar-system constraint. It is shown that the galactic halos in the f(R) gravity model tend to acquire significantly higher specific angular momentum than those in the standard {Lambda}CDM model. The largest difference in the specific angular momentum distribution between these two models occurs for the case of isolated galactic halos with mass less than 10{sup 11} h {sup -1} M {sub Sun }, which are likely least shielded by the chameleon screening mechanism. As the specific angular momentum of galactic halos is rather insensitive to other cosmological parameters, it can in principle be an independent discriminator of modified gravity. We speculate a possibility of using the relative abundance of low surface brightness galaxies (LSBGs) as a test of general relativity given that the formation of the LSBGs occurs in fast spinning dark halos.

  14. RR Lyrae to understand the Galactic halo

    NASA Astrophysics Data System (ADS)

    Fiorentino, Giuliana

    2016-08-01

    We present recent results obtained using old variable RR Lyrae stars on the Galactic halo structure and its connection with nearby dwarf galaxies. We compare the period and period-amplitude distributions for a sizeable sample of fundamental mode RR Lyrae stars (RRab) in dwarf spheroidals (~1300 stars) with those in the Galactic halo (~16'000 stars) and globular clusters (~1000 stars). RRab in dwarfs -as observed today- do not appear to follow the pulsation properties shown by those in the Galactic halo, nor they have the same properties as RRab in globulars. Thanks to the OGLE experiment we extended our comparison to massive metal-rich satellites like the dwarf irregular Large Magellanic Cloud (LMC) and the Sagittarius (Sgr) dwarf spheroidal. These massive and more metal-rich stellar systems likely have contributed to the Galactic halo formation more than classical dwarf spheroidals. Finally, exploiting the intrinsic nature of RR Lyrae as distance indicators we were able to study the period and period amplitude distributions of RRab within the Halo. It turned out that the inner and the outer Halo do show a difference that may suggest a different formation scenario (in situ vs accreted).

  15. YSO Clusters on Galactic Infrared Loops

    NASA Astrophysics Data System (ADS)

    Marton, Gábor; Kiss, Zoltán Tamás; Tóth, L. Viktor; Zahorecz, Sarolta; Pásztor, László; Ueno, Munateka; Kitamura, Yoshimi; Tamura, Motohide; Kawamura, Akiko; Onishi, Toshikazu

    The AKARI all sky survey (Murakami et al. Publ. Astron. Soc. Jpn. 59:369, 2007) was investigated for YSO candidates. Distribution of candidate sources have been analysed and compared to that of galactic CO and medium scale structures. Clustering and other inhomogenities have been found.

  16. Star formation around active galactic nuclei

    NASA Technical Reports Server (NTRS)

    Keel, William C.

    1987-01-01

    Active galactic nuclei (Seyfert nuclei and their relatives) and intense star formation can both deliver substantial amounts of energy to the vicinity of a galactic nucleus. Many luminous nuclei have energetics dominated by one of these mechanisms, but detailed observations show that some have a mixture. Seeing both phenomena at once raises several interesting questions: (1) Is this a general property of some kinds of nuclei? How many AGNs have surround starbursts, and vice versa? (2) As in 1, how many undiscovered AGNs or starbursts are hidden by a more luminous instance of the other? (3) Does one cause the other, and by what means, or do both reflect common influences such as potential well shape or level of gas flow? (4) Can surrounding star formation tell us anything about the central active nuclei, such as lifetimes, kinetic energy output, or mechanical disturbance of the ISM? These are important points in the understanding of activity and star formation in galactic nuclei. Unfortunately, the observational ways of addressing them are as yet not well formulated. Some preliminary studies are reported, aimed at clarifying the issues involved in study of the relationships between stellar and nonstellar excitement in galactic nuclei.

  17. Einstein Observations of Galactic supernova remnants

    NASA Technical Reports Server (NTRS)

    Seward, Frederick D.

    1990-01-01

    This paper summarizes the observations of Galactic supernova remnants with the imaging detectors of the Einstein Observatory. X-ray surface brightness contours of 47 remnants are shown together with gray-scale pictures. Count rates for these remnants have been derived and are listed for the HRI, IPC, and MPC detectors.

  18. Galactic Archaeology: Current Surveys and Instrumentation

    NASA Astrophysics Data System (ADS)

    Wyse, R. F. G.

    2016-10-01

    I present an overview of the science goals and achievements of ongoing spectroscopic surveys of individual stars in the nearby Universe. I include a brief discussion of the development of the field of Galactic Archaeology - using the fossil record in old stars nearby to infer how our Galaxy evolved and place the Milky Way in cosmological context.

  19. Mass Distributions Implying Flat Galactic Rotation Curves

    ERIC Educational Resources Information Center

    Keeports, David

    2010-01-01

    The rotational speeds of stars in the disc of a spiral galaxy are virtually independent of the distances of the stars from the centre of the galaxy. In common parlance, the stellar speed versus distance plot known as a galactic rotation curve is by observation typically nearly flat. This observation provides strong evidence that most galactic…

  20. Young Massive Clusters in the Galactic Center

    NASA Astrophysics Data System (ADS)

    Figer, D. F.

    2004-12-01

    The three young clusters in the Galactic Center represent the closest examples of massive starbursts and they define the upper mass limit of the Galactic cluster mass functions. In this review, I describe the characteristics and content of the Arches, Quintuplet, and Central clusters. They each are more massive than any other cluster in the Galaxy, and the Arches cluster, in particular, has a mass and age that make it ideal for studies of massive stellar evolution and dense stellar systems. A preliminary measurement indicates that the initial mass function in the Galactic center is top-heavy, suggesting an environmental effect that has otherwise been absent in similar observations for Galactic clusters. Given the relatively more evolved nature of the Quintuplet and Central clusters, these clusters contain stars in a wide range of evolutionary states, including Luminous Blue Variables and Wolf-Rayet stars. The Quintuplet cluster provides a particularly interesting view of the most massive stars that are known, the Pistol Star and FMM362. An analysis of the mass spectrum in the Arches cluster suggests an upper mass cutoff of ˜150-200 M⊙.

  1. Galactic Archeology - Requirements on Survey Spectrographs

    NASA Astrophysics Data System (ADS)

    Feltzing, S.

    2016-10-01

    Galactic Archeology is about exploring the Milky Way as a galaxy by, mainly, using its (old) stars as tracers of past events and thus to figure out the formation and evolution of our Galaxy. I will briefly outline some of the key scientific aspects of Galactic Archeology and then discuss the associated instrumentation. Gaia will forever change the way we approach this subject. However, Gaia on its own is not enough. Ground-based complementary spectroscopy is necessary to obtain full phase-space information and elemental abundances for stars fainter than the top few percent of the bright part of the Gaia catalog. I will review the requirement on instrumentation for Gaia follow-up that Galactic Archeology sets. In particular, I will discuss the requirements on radial velocity and elemental abundance determination, including a brief look at potential pitfalls in the abundance analysis (e.g., NLTE, atomic diffusion). This contribution also provides a non-exhaustive comparison of the various current and future spectrographs for Galactic Archeology. Finally, I will discuss the needs for astrophysical calibrations for the surveys and inter-survey calibrations.

  2. Modeling the evolution of galactic magnetic fields

    SciTech Connect

    Yar-Mukhamedov, D.

    2015-04-15

    An analytic model for evolution of galactic magnetic fields in hierarchical galaxy formation frameworks is introduced. Its major innovative components include explicit and detailed treatment of the physics of merger events, mass gains and losses, gravitational energy sources and delays associated with formation of large-scale magnetic fields. This paper describes the model, its implementation, and core results obtained by its means.

  3. Argon and neon in Galactic nebulae

    NASA Technical Reports Server (NTRS)

    Simpson, Janet P.; Bregman, Jesse D.; Dinerstein, H. L.; Lester, Dan F.; Rank, David M.; Witteborn, F. C.; Wooden, D. H.

    1995-01-01

    KAO observations of the 6.98 micron line of (Ar II), and KAO and ground-based observations of the 8.99 micron line of (Ar III) and the 12.8 micron line of (Ne II) are presented for a number of Galactic H II regions and planetary nebulae.

  4. On some fundamental concepts of galactic dynamics

    NASA Astrophysics Data System (ADS)

    Ossipkov, L. P.

    2013-10-01

    We discuss the following fundamental concepts of galactic dynamics: (a) regular (smoothed) and irregular (random) forces, (b) truncation of the impact parameter, (c) the invariance of the Maxwellian velocity distribution, and (d) the Jeans theorem. Dedicated to Felix Alexandrovich Tsitsin (1931-2005)

  5. Aberration in proper motions for Galactic stars

    NASA Astrophysics Data System (ADS)

    Liu, J.-C.; Xie, Y.; Zhu, Z.

    2014-12-01

    Accelerations of both the solar system barycenter (SSB) and stars in the MilkyWay cause a systematic observational effect on the stellar proper motions, which was first studied by J. Kovalevsky (2003). This paper intends to extend that work and aims to estimate the magnitude and significance of the aberration in proper motions of stars, especially in the region near the Galactic center (GC). We adopt two models for the Galactic rotation curve to evaluate the aberrational effect on the Galactic plane. We show that the effect of aberration in proper motions depends on the galactocentric distance of stars; it is dominated by the acceleration of stars in the central region of the Galaxy. Then we investigate the applicability of the theoretical expressions: if the orbital period of stars is only a fraction of the light time from the star to the SSB, the expression with approximation proposed by Kovalevsky is not appropriate. With a more suitable formulation, we found that the aberration has no effect on the determination of the stellar orbits on the celestial sphere. In the future this aberrational effect under consideration should be considered with high-accurate astrometry, particularly in constructing the Gaia celestial reference system realized by Galactic stars.

  6. Tests of two convection theories for red giant and red supergiant envelopes

    NASA Technical Reports Server (NTRS)

    Stothers, Richard B.; Chin, Chao-Wen

    1995-01-01

    Two theories of stellar envelope convection are considered here in the context of red giants and red supergiants of intermediate to high mass: Boehm-Vitense's standard mixing-length theory (MLT) and Canuto & Mazzitelli's new theory incorporating the full spectrum of turbulence (FST). Both theories assume incompressible convection. Two formulations of the convective mixing length are also evaluated: l proportional to the local pressure scale height (H(sub P)) and l proportional to the distance from the upper boundary of the convection zone (z). Applications to test both theories are made by calculating stellar evolutionary sequences into the red zone (z). Applications to test both theories are made by calculating stellar evolutionary sequences into the red phase of core helium burning. Since the theoretically predicted effective temperatures for cool stars are known to be sensitive to the assigned value of the mixing length, this quantity has been individually calibrated for each evolutionary sequence. The calibration is done in a composite Hertzsprung-Russell diagram for the red giant and red supergiant members of well-observed Galactic open clusters. The MLT model requires the constant of proportionality for the convective mixing length to vary by a small but statistically significant amount with stellar mass, whereas the FST model succeeds in all cases with the mixing lenghth simply set equal to z. The structure of the deep stellar interior, however, remains very nearly unaffected by the choices of convection theory and mixing lenghth. Inside the convective envelope itself, a density inversion always occurs, but is somewhat smaller for the convectively more efficient MLT model. On physical grounds the FST model is preferable, and seems to alleviate the problem of finding the proper mixing length.

  7. SDP Herschel/HiFi results from post-AGB sources

    NASA Astrophysics Data System (ADS)

    Alcolea Jimanez, J.; Bujarrabal, V.; Soria-Ruiz, R.; Planesas, P.; Cernicharo, J.; Decin, L.; Dominik, C.; Justtanont, K.; de Koter, A.; Marston, A. P.; Melnick, G.; Menten, K. M.; Neufeld, D.; Olofsson, H.; Pulecka, M.; Schmidt, M.; Schoeier, F. L.; Szczerba, C.; Teyssier, D.; Waters, L. B. F. M.; Quintana-Lacaci, G.; Guesten, R.

    The first Herschel/HiFi data on pPNe and young PNe are being obtained, providing, for the first time, systematic observations of high-excitation molecular lines from these sources with high spectral resolution. The telescope and all telescopes sub-systems are performing as expected, and so the data are of very good quality. The high spectral resolution provided by the heterodyne detection technique allows the detection of spectra of high velocity resolution (always better than 1 km/s), in which the different dynamical components of the nebulae can be clearly separated and identified. This data allows, for the first time, systematically study of the warm molecular component in these objects, including in particular the study of thermal lines of water vapor, which of course cannot be done from the ground. In this poster we summarize the very first results on pPNe and PNe obtained with Herschel/HiFi. In particular we note the detection of intense emission from the bipolar fast flows in the C-rich pPNe CRL 618. A crude comparison with the existing models for the source, indicates that this emission comes from the base of the very fast shock-accelerated jets. Results on additional sources, like NGC 6302, the Red Rectangle, and others, are also discussed.

  8. PTF10fqs: A Luminous Red Nova in the Spiral Messier 99

    NASA Astrophysics Data System (ADS)

    Kasliwal, Mansi; Helou, George; Surace, Jason; Kulkarni, Shri

    2010-06-01

    On April 16, 2010 we discovered a rare transient (PTF10fqs) in the luminosity gap between novae and supernovae with the Palomar Transient Factory. PTF10fqs is located on a spiral arm in M99, a member of the Virgo Cluster. On April 18, we obtained a Gemini spectrum and on April 20, multi-color photometry with the Palomar 60-inch. The explosion signature resembles that of a class of 'Luminous Red Novae'; only two other such transients are known. A plethora of models have been proposed: stellar merger, e-capture on AGB star, weird nova and weird supernova. Here, we propose MIR photometry to determine the total energetics of the event and as a unique tracer of the circumstellar dust. Together with our ongoing multi-wavelength (optical, NIR, radio, UV and X-ray) follow-up of PTF10fqs, we hope to make progress in deciphering the nature of this class.

  9. Spectropolarimetric test of the relativistic disk model for the broad emission lines of active galactic nuclei

    NASA Technical Reports Server (NTRS)

    Chen, Kaiyou; Halpern, Jules P.

    1990-01-01

    Previously, it was claimed that the broad emission lines of the radio galaxy Arp 102B can be fitted by the line profile from a simple relativistic Keplerian thin disk. It was argued that the lines originating from the relativistic accretion disk could be polarized due to electron scattering, which is likely to be the dominant opacity in the line-emitting region of Arp 102B. In the present work, the expected polarization properties of these broad emission lines are calculated. The percentage of polarization depends strongly on the inclination angle. For some angles, the red peak of the polarized, double-peaked line profile can be higher than the blue peak. This is in contrast to the total line profile, in which the blue peak is always higher than the red one. Spectropolarimetric observations could, therefore, provide an independent test of the relativistic disk model for the broad emission lines of Arp 102B and other active galactic nuclei.

  10. A cost effective and operational methodology for wall to wall Above Ground Biomass (AGB) and carbon stocks estimation and mapping: Nepal REDD+

    NASA Astrophysics Data System (ADS)

    Gilani, H., Sr.; Ganguly, S.; Zhang, G.; Koju, U. A.; Murthy, M. S. R.; Nemani, R. R.; Manandhar, U.; Thapa, G. J.

    2015-12-01

    Nepal is a landlocked country with 39% forest cover of the total land area (147,181 km2). Under the Forest Carbon Partnership Facility (FCPF) and implemented by the World Bank (WB), Nepal chosen as one of four countries best suitable for results-based payment system for Reducing Emissions from Deforestation and Forest Degradation (REDD and REDD+) scheme. At the national level Landsat based, from 1990 to 2000 the forest area has declined by 2%, i.e. by 1467 km2, whereas from 2000 to 2010 it has declined only by 0.12% i.e. 176 km2. A cost effective monitoring and evaluation system for REDD+ requires a balanced approach of remote sensing and ground measurements. This paper provides, for Nepal a cost effective and operational 30 m Above Ground Biomass (AGB) estimation and mapping methodology using freely available satellite data integrated with field inventory. Leaf Area Index (LAI) generated based on propose methodology by Ganguly et al. (2012) using Landsat-8 the OLI cloud free images. To generate tree canopy height map, a density scatter graph between the Geoscience Laser Altimeter System (GLAS) on the Ice, Cloud, and Land Elevation Satellite (ICESat) estimated maximum height and Landsat LAI nearest to the center coordinates of the GLAS shots show a moderate but significant exponential correlation (31.211*LAI0.4593, R2= 0.33, RMSE=13.25 m). From the field well distributed circular (750m2 and 500m2), 1124 field plots (0.001% representation of forest cover) measured which were used for estimation AGB (ton/ha) using Sharma et al. (1990) proposed equations for all tree species of Nepal. A satisfactory linear relationship (AGB = 8.7018*Hmax-101.24, R2=0.67, RMSE=7.2 ton/ha) achieved between maximum canopy height (Hmax) and AGB (ton/ha). This cost effective and operational methodology is replicable, over 5-10 years with minimum ground samples through integration of satellite images. Developed AGB used to produce optimum fuel wood scenarios using population and road

  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. Stellar evolution of low and intermediate-mass stars. IV. Hydrodynamically-based overshoot and nucleosynthesis in AGB stars.

    NASA Astrophysics Data System (ADS)

    Herwig, F.; Bloecker, T.; Schoenberner, D.; El Eid, M.

    1997-08-01

    The focus of this study is on the treatment of those stellar regions immediately adjacent to convective zones. The results of hydrodynamical simulations by Freytag et al. (1996A&A...313..497F) show that the motion of convective elements extends well beyond the boundary of the convectively unstable region. We have applied their parametrized description of the corresponding velocities to the treatment of overshoot in stellar evolution calculations up to the AGB (Pop.I, M_ZAMS_=3Msun_). Our calculations show the 3^rd^ dredge-up already at the 7^th^ thermal pulse (TP), and the dredge-up parameter reaches λ=0.6 during the next five pulses. Accordingly, the amount of dredged up ^12^C is up to 10^-3^Msun_. Our models develope a small so-called ^13^C-pocket consisting of a few 10^-7^ Msun_. Finally, this treatment of boundaries of convective regions leads to intershell abundances of typically (^4^He/^12^C/^16^O)=(23/50/25) (compared to (70/26/1) in the standard treatment).

  13. DUST IN ACTIVE GALACTIC NUCLEI: ANOMALOUS SILICATE TO OPTICAL EXTINCTION RATIOS?

    SciTech Connect

    Lyu, Jianwei; Hao, Lei; Li, Aigen

    2014-09-01

    Dust plays a central role in the unification theory of active galactic nuclei (AGNs). However, little is known about the nature (e.g., size, composition) of the dust that forms a torus around the AGN. In this Letter, we report a systematic exploration of the optical extinction (A{sub V} ) and the silicate absorption optical depth (Δτ{sub 9.7}) of 110 type 2 AGNs. We derive A{sub V} from the Balmer decrement based on the Sloan Digital Sky Survey data, and Δτ{sub 9.7} from the Spitzer/InfraRed Spectrograph data. We find that with a mean ratio of (A{sub V} /Δτ{sub 9.7}) ≲ 5.5, the optical-to-silicate extinction ratios of these AGNs are substantially lower than that of the Galactic diffuse interstellar medium (ISM) for which A{sub V} /Δτ{sub 9.7} ≈ 18.5. We argue that the anomalously low A{sub V} /Δτ{sub 9.7} ratio could be due to the predominance of larger grains in the AGN torus compared to that in the Galactic diffuse ISM.

  14. Target Selection for the Apache Point Observatory Galactic Evolution Experiment (APOGEE)

    NASA Astrophysics Data System (ADS)

    Zasowski, G.; Johnson, Jennifer A.; Frinchaboy, P. M.; Majewski, S. R.; Nidever, D. L.; Rocha Pinto, H. J.; Girardi, L.; Andrews, B.; Chojnowski, S. D.; Cudworth, K. M.; Jackson, K.; Munn, J.; Skrutskie, M. F.; Beaton, R. L.; Blake, C. H.; Covey, K.; Deshpande, R.; Epstein, C.; Fabbian, D.; Fleming, S. W.; Garcia Hernandez, D. A.; Herrero, A.; Mahadevan, S.; Mészáros, Sz.; Schultheis, M.; Sellgren, K.; Terrien, R.; van Saders, J.; Allende Prieto, C.; Bizyaev, D.; Burton, A.; Cunha, K.; da Costa, L. N.; Hasselquist, S.; Hearty, F.; Holtzman, J.; García Pérez, A. E.; Maia, M. A. G.; O'Connell, R. W.; O'Donnell, C.; Pinsonneault, M.; Santiago, B. X.; Schiavon, R. P.; Shetrone, M.; Smith, V.; Wilson, J. C.

    2013-10-01

    The Apache Point Observatory Galactic Evolution Experiment (APOGEE) is a high-resolution infrared spectroscopic survey spanning all Galactic environments (i.e., bulge, disk, and halo), with the principal goal of constraining dynamical and chemical evolution models of the Milky Way. APOGEE takes advantage of the reduced effects of extinction at infrared wavelengths to observe the inner Galaxy and bulge at an unprecedented level of detail. The survey's broad spatial and wavelength coverage enables users of APOGEE data to address numerous Galactic structure and stellar populations issues. In this paper we describe the APOGEE targeting scheme and document its various target classes to provide the necessary background and reference information to analyze samples of APOGEE data with awareness of the imposed selection criteria and resulting sample properties. APOGEE's primary sample consists of ~105 red giant stars, selected to minimize observational biases in age and metallicity. We present the methodology and considerations that drive the selection of this sample and evaluate the accuracy, efficiency, and caveats of the selection and sampling algorithms. We also describe additional target classes that contribute to the APOGEE sample, including numerous ancillary science programs, and we outline the targeting data that will be included in the public data releases.

  15. On the Galactic Spin of Barred Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Cervantes-Sodi, Bernardo; Li, Cheng; Park, Changbom; Wang, Lixin

    2013-09-01

    We present a study of the connection between the galactic spin parameter (λ d ) and the bar fraction in a volume-limited sample of 10,674 disk galaxies drawn from the Sloan Digital Sky Survey Data Release 7. The galaxies in our sample are visually classified into one of three groups: non-barred galaxies and galaxies hosting long or short bars, respectively. We find that the spin distributions of these three classes are statistically different, with galaxies hosting long bars having the lowest λ d values, followed by non-barred galaxies, while galaxies with short bars present typically high spin parameters. The bar fraction presents its maximum at low to intermediate λ d values for the case of long bars, while the maximum for short bars is at high λ d . This bimodality is in good agreement with previous studies finding longer bars hosted by luminous, massive, red galaxies with a low content of cold gas, while short bars were found in low luminosity, low mass, blue galaxies that were typically gas rich. In addition, the rise and fall of the bar fraction as a function of λ d , within the long-bar sample shown in our results, can be explained as a result of two competing factors: the self-gravity of the disk that enhances bar instabilities and the support by random motions, instead of ordered rotational motion, that prevents the formation/growth of bars.

  16. ON THE GALACTIC SPIN OF BARRED DISK GALAXIES

    SciTech Connect

    Cervantes-Sodi, Bernardo; Li, Cheng; Wang, Lixin; Park, Changbom

    2013-09-20

    We present a study of the connection between the galactic spin parameter (λ{sub d}) and the bar fraction in a volume-limited sample of 10,674 disk galaxies drawn from the Sloan Digital Sky Survey Data Release 7. The galaxies in our sample are visually classified into one of three groups: non-barred galaxies and galaxies hosting long or short bars, respectively. We find that the spin distributions of these three classes are statistically different, with galaxies hosting long bars having the lowest λ{sub d} values, followed by non-barred galaxies, while galaxies with short bars present typically high spin parameters. The bar fraction presents its maximum at low to intermediate λ{sub d} values for the case of long bars, while the maximum for short bars is at high λ{sub d}. This bimodality is in good agreement with previous studies finding longer bars hosted by luminous, massive, red galaxies with a low content of cold gas, while short bars were found in low luminosity, low mass, blue galaxies that were typically gas rich. In addition, the rise and fall of the bar fraction as a function of λ{sub d}, within the long-bar sample shown in our results, can be explained as a result of two competing factors: the self-gravity of the disk that enhances bar instabilities and the support by random motions, instead of ordered rotational motion, that prevents the formation/growth of bars.

  17. THE NATURE OF OPTICALLY DULL ACTIVE GALACTIC NUCLEI IN COSMOS

    SciTech Connect

    Trump, Jonathan R.; Impey, Chris D.; Gabor, Jared M.; Taniguchi, Yoshi; Nagao, Tohru; Shioya, Yasuhiro; Brusa, Marcella; Civano, Francesca; Elvis, Martin; Kelly, Brandon C.; Huchra, John P.; Jahnke, Knud; Koekemoer, Anton M.; Salvato, Mara; Capak, Peter; Scoville, Nick Z.; Kartaltepe, Jeyhan S.; Lanzuisi, Giorgio; McCarthy, Patrick J.; Maineri, Vincenzo

    2009-11-20

    We present infrared, optical, and X-ray data of 48 X-ray bright, optically dull active galactic nuclei (AGNs) in the COSMOS field. These objects exhibit the X-ray luminosity of an AGN but lack broad and narrow emission lines in their optical spectrum. We show that despite the lack of optical emission lines, most of these optically dull AGNs are not well described by a typical passive red galaxy spectrum: instead they exhibit weak but significant blue emission like an unobscured AGN. Photometric observations over several years additionally show significant variability in the blue emission of four optically dull AGNs. The nature of the blue and infrared emission suggest that the optically inactive appearance of these AGNs cannot be caused by obscuration intrinsic to the AGNs. Instead, up to approx70% of optically dull AGNs are diluted by their hosts, with bright or simply edge-on hosts lying preferentially within the spectroscopic aperture. The remaining approx30% of optically dull AGNs have anomalously high f{sub X} /f{sub O} ratios and are intrinsically weak, not obscured, in the optical. These optically dull AGNs are best described as a weakly accreting AGN with a truncated accretion disk from a radiatively inefficient accretion flow.

  18. The suppression of star formation by powerful active galactic nuclei.

    PubMed

    Page, M J; Symeonidis, M; Vieira, J D; Altieri, B; Amblard, A; Arumugam, V; Aussel, H; Babbedge, T; Blain, A; Bock, J; Boselli, A; Buat, V; Castro-Rodríguez, N; Cava, A; Chanial, P; Clements, D L; Conley, A; Conversi, L; Cooray, A; Dowell, C D; Dubois, E N; Dunlop, J S; Dwek, E; Dye, S; Eales, S; Elbaz, D; Farrah, D; Fox, M; Franceschini, A; Gear, W; Glenn, J; Griffin, M; Halpern, M; Hatziminaoglou, E; Ibar, E; Isaak, K; Ivison, R J; Lagache, G; Levenson, L; Lu, N; Madden, S; Maffei, B; Mainetti, G; Marchetti, L; Nguyen, H T; O'Halloran, B; Oliver, S J; Omont, A; Panuzzo, P; Papageorgiou, A; Pearson, C P; Pérez-Fournon, I; Pohlen, M; Rawlings, J I; Rigopoulou, D; Riguccini, L; Rizzo, D; Rodighiero, G; Roseboom, I G; Rowan-Robinson, M; Sánchez Portal, M; Schulz, B; Scott, D; Seymour, N; Shupe, D L; Smith, A J; Stevens, J A; Trichas, M; Tugwell, K E; Vaccari, M; Valtchanov, I; Viero, M; Vigroux, L; Wang, L; Ward, R; Wright, G; Xu, C K; Zemcov, M

    2012-05-09

    The old, red stars that constitute the bulges of galaxies, and the massive black holes at their centres, are the relics of a period in cosmic history when galaxies formed stars at remarkable rates and active galactic nuclei (AGN) shone brightly as a result of accretion onto black holes. It is widely suspected, but unproved, that the tight correlation between the mass of the black hole and the mass of the stellar bulge results from the AGN quenching the surrounding star formation as it approaches its peak luminosity. X-rays trace emission from AGN unambiguously, whereas powerful star-forming galaxies are usually dust-obscured and are brightest at infrared and submillimetre wavelengths. Here we report submillimetre and X-ray observations that show that rapid star formation was common in the host galaxies of AGN when the Universe was 2-6 billion years old, but that the most vigorous star formation is not observed around black holes above an X-ray luminosity of 10(44) ergs per second. This suppression of star formation in the host galaxy of a powerful AGN is a key prediction of models in which the AGN drives an outflow, expelling the interstellar medium of its host and transforming the galaxy's properties in a brief period of cosmic time.

  19. MAPPING DIFFERENTIAL REDDENING IN THE INNER GALACTIC GLOBULAR CLUSTER SYSTEM

    SciTech Connect

    Alonso-Garcia, Javier; Mateo, Mario; Sen, Bodhisattva; Banerjee, Moulinath; Von Braun, Kaspar E-mail: mmateo@umich.edu E-mail: moulib@umich.edu

    2011-05-15

    A serious limitation in the study of many globular clusters-especially those located near the Galactic center-has been the existence of large and differential extinction by foreground dust. In a series of papers, we intend to map the differential extinction and remove its effects, using a new dereddening technique, in a sample of clusters in the direction of the inner Galaxy, observed using the Magellan 6.5 m telescope and the Hubble Space Telescope. These observations and their analysis will let us produce high-quality color-magnitude diagrams of these poorly studied clusters that will allow us to determine these clusters' relative ages, distances, and chemistry and to address important questions about the formation and the evolution of the inner Galaxy. We also intend to use the maps of the differential extinction to sample and characterize the interstellar medium along the numerous low-latitude lines of sight where the clusters in our sample lie. In this first paper, we describe in detail our dereddening method along with the powerful statistics tools that allow us to apply it, and we show the kind of results that we can expect, applying the method to M62, one of the clusters in our sample. The width of the main sequence and lower red giant branch narrows by a factor of two after applying our dereddening technique, which will significantly help to constrain the age, distance, and metallicity of the cluster.

  20. The Suppression of Star Formation by Powerful Active Galactic Nuclei

    NASA Technical Reports Server (NTRS)

    Dwek, E.

    2012-01-01

    The old, red stars that constitute the bulges of galaxies, and the massive black holes at their centres, are the relics of a period in cosmic history when galaxies formed stars at remarkable rates and active galactic nuclei (AGN) shone brightly as a result of accretion onto black holes. It is widely suspected, but unproved, that the tight corre1ation between the mass of the black hole and the mas. of the stellar bulge results from the AGN quenching the surrounding star formation as it approaches its peak luminosity. X-rays trace emission from AGN unambiguously, whereas powerful star-forming ga1axies are usually dust-obscured and are brightest at infrared and submillimeter wavelengths. Here we report submillimetre and X-ray observations that show that rapid star formation was common in the host galaxies of AGN when the Universe was 2-6 billion years old, but that the most vigorous star formation is not observed around black holes above an X-ray luminosity of 10(exp 44) ergs per second. This suppression of star formation in the host galaxy of a powerful AGN is a key prediction of models in which the AGN drives an outflow, expe11ing the interstellar medium of its host and transforming the galaxy's properties in a brief period of cosmic time.

  1. 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.

  2. The angular clustering of WISE-selected active galactic nuclei: Different halos for obscured and unobscured active galactic nuclei

    SciTech Connect

    Donoso, E.; Yan, Lin; Stern, D.; Assef, R. J.

    2014-07-01

    We calculate the angular correlation function for a sample of ∼170,000 active galactic nuclei (AGNs) extracted from the Wide-field Infrared Survey Explorer (WISE) catalog, selected to have red mid-IR colors (W1 – W2 > 0.8) and 4.6 μm flux densities brighter than 0.14 mJy). The sample is expected to be >90% reliable at identifying AGNs and to have a mean redshift of (z) = 1.1. In total, the angular clustering of WISE AGNs is roughly similar to that of optical AGNs. We cross-match these objects with the photometric Sloan Digital Sky Survey catalog and distinguish obscured sources with r – W2 > 6 from bluer, unobscured AGNs. Obscured sources present a higher clustering signal than unobscured sources. Since the host galaxy morphologies of obscured AGNs are not typical red sequence elliptical galaxies and show disks in many cases, it is unlikely that the increased clustering strength of the obscured population is driven by a host galaxy segregation bias. By using relatively complete redshift distributions from the COSMOS survey, we find that obscured sources at (z) ∼ 0.9 have a bias of b = 2.9 ± 0.6 and are hosted in dark matter halos with a typical mass of log (M/M {sub ☉} h {sup –1}) ∼ 13.5. In contrast, unobscured AGNs at (z) ∼ 1.1 have a bias of b = 1.6 ± 0.6 and inhabit halos of log (M/M {sub ☉} h {sup –1}) ∼ 12.4. These findings suggest that obscured AGNs inhabit denser environments than unobscured AGNs, and they are difficult to reconcile with the simplest AGN unification models, where obscuration is driven solely by orientation.

  3. Galactic Teamwork Makes Distant Bubbles

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-03-01

    During the period of reionization that followed the dark ages of our universe, hydrogen was transformed from a neutral state, which is opaque to radiation, to an ionized one, which is transparent to radiation. But what generated the initial ionizing radiation? The recent discovery of multiple distant galaxies offers evidence for how this process occurred.Two Distant GalaxiesWe believe reionization occurred somewhere between a redshift of z = 6 and 7, because Ly-emitting galaxies drop out at roughly this redshift. Beyond this distance, were generally unable to see the light from these galaxies, because the universe is no longer transparent to their emission. This is not always the case, however: if a bubble of ionized gas exists around a distant galaxy, the radiation can escape, allowing us to see the galaxy.This is true of two recently-discovered Ly-emitting galaxies, confirmed to be at a redshift of z~7 and located near one another in a region known as the Bremer Deep Field. The fact that were able to see the radiation from these galaxies means that they are in an ionized HII region presumably one of the earlier regions to have become reionized in the universe.But on their own, neither of these galaxies is capable of generating an ionized bubble large enough for their light to escape. So what ionized the region around them, and what does this mean for our understanding of how reionization occurred in the universe?A Little Help From FriendsLocation in different filters of the objects in the Hubble Bremer Deep Field catalog. The z~7 selection region is outlined by the grey box. BDF-521 and BDF-3299 were the two originally discovered galaxies; the remaining red markers indicate the additional six galaxies discovered in the same region. [Castellano et al. 2016]A team of scientists led by Marco Castellano (Rome Observatory, INAF) investigated the possibility that there are other, faint galaxies near these two that have helped to ionize the region. Performing a survey

  4. 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.

  5. A starburst region at the tip of the Galactic bar around l=347-350

    NASA Astrophysics Data System (ADS)

    Marco, Amparo; Negueruela, Ignacio; González-Fernández, Carlos; Maíz-Apellániz, Jesús; Dorda, Ricardo; Clark, J. Simon

    2015-08-01

    In the past few years, several clusters of red supergiants have been discovered in a small region of the Milky Way, close to the base of the Scutum-Crux Arm and the tip of the Long Bar, between l=24º and l=29º. According to the number of observed red supergiants and using population synthesis models, they must contain very large stellar populations to harbour so many RSGs, some of them being candidates to the most massive young clusters in the Galaxy. These massive open clusters are part of a huge structure most likely containing hundreds of red supergiants. These results suggest that the Scutum complex represents a giant star formation region triggered by dynamical excitation by the Galactic bar, whose tip is believed to intersect the Scutum-Crux Arm close to this region. If this scenario is correct, a similar structure would be expected close to the opposite end of the Galactic long bar. We must find in an area between l=347º-350º (these sight lines include the expected location of the far tip of the Galactic bar in the model of González-Fernández et al. (2012)) likely candidates to very massive open clusters.We are carrying out a comprehensive optical and infrared photometric and spectroscopic study of this region containing the open clusters VdBH 222, Teutsch 85 and their surroundings. We have analyzed the population of VdBH 222 and we have found a large population of luminous supergiants and OB stars. The cluster lies behind ~7.5 mag of extinction and has a probable distance of ~ 10 kpc and an age of ~12 Ma. VdBH 222 is a young massive cluster with a likely mass > 20000 Msolar. Now, we are analyzing the population of the open cluster Teutsch 85 and surroundings, finding a numerous population of supergiants.In this work, we will discuss the possible role of the Galactic bar in triggering the formation of starburst clusters.

  6. Cobb's Red Cabbage Indicator.

    ERIC Educational Resources Information Center

    Cobb, Vicki

    1998-01-01

    Describes the use of an indicator made from the pigment in red cabbage. Cabbage is grated then soaked in water. When the water is a strong red, the cabbage is strained out. The cabbage-juice indicator is then used to test for acids and bases. Includes a list of good foods to test for acidity and alkalinity. (PVD)

  7. The near-infrared counterpart of a variable galactic plane radio source

    NASA Technical Reports Server (NTRS)

    Margon, Bruce; Phillips, Andrew C.; Ciardullo, Robin; Jacoby, George H.

    1992-01-01

    A near-infrared counterpart to the highly variable, unresolved galactic plane radio source GT 0116 + 622 is identified. This source is of particular interest, as it has been previously suggested to be the counterpart of the gamma-ray source Cas gamma-l. The present NIR and red images detect a faint, spatially extended (3 arcsec FWHM), very red object coincident with the radio position. There is complex spatial structure which may be due in part to an unrelated superposed foreground object. Observations on multiple nights show no evidence for flux variability, despite the high amplitude variability on a time-scale of days reported for the radio source. The data are consistent with an interpretation of GT 0116 + 622 as an unusually variable, obscured active galaxy at a distance of several hundred megaparsecs, although more exotic, and in particular galactic, interpretations cannot yet be ruled out. If the object is extragalactic, the previously suggested identification with the gamma-ray source would seem unlikely.

  8. Gravitational lensing of active galactic nuclei.

    PubMed Central

    Hewitt, J N

    1995-01-01

    Most of the known cases of strong gravitational lensing involve multiple imaging of an active galactic nucleus. The properties of lensed active galactic nuclei make them promising systems for astrophysical applications of gravitational lensing; in particular, they show structure on scales of milliseconds of arc to tens of seconds of arc, they are variable, and they are polarized. More than 20 cases of strong gravitational lenses are now known, and about half of them are radio sources. High-resolution radio imaging is making possible the development of well-constrained lens models. Variability studies at radio and optical wavelengths are beginning to yield results of astrophysical interest, such as an independent measure of the distance scale and limits on source sizes. PMID:11607613

  9. Galactic Cosmic Rays in the Outer Heliosphere

    NASA Technical Reports Server (NTRS)

    Florinski, V.; Washimi, H.; Pogorelov, N. V.; Adams, J. H.

    2010-01-01

    We report a next generation model of galactic cosmic ray (GCR) transport in the three dimensional heliosphere. Our model is based on an accurate three-dimensional representation of the heliospheric interface. This representation is obtained by taking into account the interaction between partially ionized, magnetized plasma flows of the solar wind and the local interstellar medium. Our model reveals that after entering the heliosphere GCRs are stored in the heliosheath for several years. The preferred GCR entry locations are near the nose of the heliopause and at high latitudes. Low-energy (hundreds of MeV) galactic ions observed in the heliosheath have spent, on average, a longer time in the solar wind than those observed in the inner heliosphere, which would explain their cooled-off spectra at these energies. We also discuss radial gradients in the heliosheath and the implications for future Voyager observations

  10. A Speeding Binary in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-04-01

    The recent discovery of a hyper-velocity binary star system in the halo of the Milky Way poses a mystery: how was this system accelerated to its high speed?Accelerating StarsUnlike the uniform motion in the Galactic disk, stars in the Milky Ways halo exhibit a huge diversity of orbits that are usually tilted relative to the disk and have a variety of speeds. One type of halo star, so-called hyper-velocity stars, travel with speeds that can approach the escape velocity of the Galaxy.How do these hyper-velocity stars come about? Assuming they form in the Galactic disk, there are multiple proposed scenarios through which they could be accelerated and injected into the halo, such as:Ejection after a close encounter with the supermassive black hole at the Galactic centerEjection due to a nearby supernova explosionEjection as the result of a dynamical interaction in a dense stellar population.Further observations of hyper-velocity stars are necessary to identify the mechanism responsible for their acceleration.J1211s SurpriseModels of J1211s orbit show it did not originate from the Galactic center (black dot). The solar symbol shows the position of the Sun and the star shows the current position of J1211. The bottom two panels show two depictions(x-y plane and r-z plane) of estimated orbits of J1211 over the past 10 Gyr. [Nmeth et al. 2016]To this end, a team of scientists led by Pter Nmeth (Friedrich Alexander University, Erlangen-Nrnberg) recently studied the candidate halo hyper-velocity star SDSS J121150.27+143716.2. The scientists obtained spectroscopy of J1211 using spectrographs at the Keck Telescope in Hawaii and ESOs Very Large Telescope in Chile. To their surprise, they discovered the signature of a companion in the spectra: J1211 is actually a binary!Nmeth and collaborators found that J1211, located roughly 18,000 light-years away, is moving at a rapid ~570 km/s relative to the galactic rest frame. The binary system consists of a hot (30,600 K) subdwarf and a

  11. A PUZZLE INVOLVING GALACTIC BULGE MICROLENSING EVENTS

    SciTech Connect

    Cohen, Judith G.; Gould, Andrew; Johnson, Jennifer A.; Thompson, Ian B.; Feltzing, Sofia; Bensby, Thomas; Huang Wenjin; Melendez, Jorge; Lucatello, Sara; Asplund, Martin E-mail: gould@astronomy.ohio-state.edu E-mail: ian@obs.carnegiescience.edu E-mail: tbensby@eso.org E-mail: jorge@astro.up.pt E-mail: asplund@MPA-Garching.MPG.DE

    2010-03-01

    We study a sample of 16 microlensed Galactic bulge main-sequence turnoff region stars for which high-dispersion spectra have been obtained with detailed abundance analyses. We demonstrate that there is a very strong and highly statistically significant correlation between the maximum magnification of the microlensed bulge star and the value of the [Fe/H] deduced from the high resolution spectrum of each object. Physics demands that this correlation, assuming it to be real, be the result of some sample bias. We suggest several possible explanations, but are forced to reject them all, and are left puzzled. To obtain a reliable metallicity distribution in the Galactic bulge based on microlensed dwarf stars, it will be necessary to resolve this issue through the course of additional observations.

  12. Brown dwarfs as dark galactic halos

    NASA Technical Reports Server (NTRS)

    Adams, Fred C.; Walker, Terry P.

    1990-01-01

    The possibility that the dark matter in galactic halos can consist of brown dwarf stars is considered. The radiative signature for such halos consisting solely of brown dwarfs is calculated, and the allowed range of brown dwarf masses, the initial mass function (IMF), the stellar properties, and the density distribution of the galactic halo are discussed. The prediction emission from the halo is compared with existing observations. It is found that, for any IMF of brown dwarfs below the deuterium burning limit, brown dwarf halos are consistent with observations. Brown dwarf halos cannot, however, explain the recently observed near-IR background. It is shown that future satellite missions will either detect brown dwarf halos or place tight constraints on the allowed range of the IMF.

  13. On the biological hazard of galactic antinuclei

    NASA Technical Reports Server (NTRS)

    Wilson, J. W.; Townsend, L. W.; Buck, W. W.

    1986-01-01

    The interaction of antinuclei in the galactic cosmic-ray beam with biological systems is studied. A nuclei-antinuclei annihilation event observed in nuclear emulsion near the end of the slowing-down trajectories of singly charged particle is discussed. An annihilation event that occurred by capture of the antinucleus into an atomic orbital followed by cascade to or near the ground atomic state and subsequent annihilation with the nuclear material of the atom is described. Microdosimetric quantities relevant to potential biological hazards are estimated. The average linear-energy-transfer spectrum for galactic cosmic ray antinuclei annihilation events in tissues is presented. It is observed that the annihilation in tissues occurs mainly in O and the heavier elements around K.

  14. Does electromagnetic radiation accelerate galactic cosmic rays

    NASA Technical Reports Server (NTRS)

    Eichler, D.

    1977-01-01

    The 'reactor' theories of Tsytovich and collaborators (1973) of cosmic-ray acceleration by electromagnetic radiation are examined in the context of galactic cosmic rays. It is shown that any isotropic synchrotron or Compton reactors with reasonable astrophysical parameters can yield particles with a maximum relativistic factor of only about 10,000. If they are to produce particles with higher relativistic factors, the losses due to inverse Compton scattering of the electromagnetic radiation in them outweigh the acceleration, and this violates the assumptions of the theory. This is a critical restriction in the context of galactic cosmic rays, which have a power-law spectrum extending up to a relativistic factor of 1 million.

  15. Galactic transients from the OGLE survey

    NASA Astrophysics Data System (ADS)

    Mroz, Przemek

    2016-07-01

    For many years, there were not any systematic, large-scale surveys for transients in the Milky Way and the Magellanic Clouds. This gap is being filled by discoveries from the OGLE survey, which has been regularly monitoring the densest sky regions (the Galactic bulge and disk, the Magellanic System) for over twenty years. The OGLE collection of Galactic transients contains several dozen classical novae and over a thousand other cataclysmic variables. I will tell how to select transients from billions of sources observed by the OGLE every night. I will show how the properties of classical novae depend on the underlying stellar population (and the star formation history). I will also discuss the preliminary results of the search for transients in the Milky Way disk from the OGLE-IV Galaxy Variability Survey. Finally, I will show some transients of yet unknown origin and present the OGLE-IV real time monitoring systems.

  16. The FLAMINGOS-2 Galactic Center Survey

    NASA Astrophysics Data System (ADS)

    Eikenberry, Stephen S.

    2008-05-01

    Upon commissioning on Gemini South, FLAMINGOS-2 will be one of the most powerful wide-field near-infrared imagers and multi-object spectrographs ever built for use on 8-meter-class telescopes. In order to take best advantage of the strengths of FLAMINGOS-2 early in its life cycle, the instrument team has proposed to use 21 nights of Gemini guaranteed time in 3 surveys-the FLAMINGOS-2 Early Science Surveys (F2ESS). The F2ESS will encompass 3 corresponding science themes-the Galactic Center, galaxy evolution, and star formation. In this paper, I review the design performance and status of FLAMINGOS-2, and describe the planned FLAMINGOS-2 Galactic Center Survey.

  17. Formation Models of the Galactic Bulge

    NASA Astrophysics Data System (ADS)

    Gerhard, O.

    2015-05-01

    The Galactic bulge is now considered to be the inner three-dimensional part of the Milky Way's bar. It has a peanut shape and is characterized by cylindrical rotation. In N-body simulations, box/peanut bulges arise from disks through bar and buckling instabilities. Models of this kind explain much of the structure and kinematics of the Galactic bulge and, in principle, also its vertical metallicity gradient. Cosmological disk galaxy formation models with high resolution and improved feedback models are now able to generate late-type disk galaxies with disk-like or barred bulges. These bulges often contain an early collapse stellar population and a population driven by later disk instabilities. Due to the inside-out disk formation, these bulges can be predominantly old, similar to the Milky Way bulge.

  18. Ambartsumyan's concept of active galactic nuclei

    NASA Astrophysics Data System (ADS)

    Khachikian, E. Ye.

    2010-01-01

    As Victor Ambartsumyan, himself, noted, the concept of active galactic nuclei occupies a special place among his scientific ideas. It was proposed more than half a century ago and was recognized by the U.S. National Academy of Sciences as revolutionary, on a copernican scale. However, by no means all of its propositions were accepted at once by large parts of the astronomy community. Nevertheless, as the American astrophysicist A. R. Sandage has written, “today, not one astronomer would deny the mystery surrounding the nuclei of galaxies or that the first to recognize the rich reward held in this treasury was Viktor Ambartsumian.” The purpose of this article is to acquaint the reader with the major stages in the formation and development of the concept of active galactic nuclei and with some of the work on this topic done at the Byurakan and other astrophysical observatories throughout the world.

  19. Molecular clouds and galactic spiral structure

    NASA Technical Reports Server (NTRS)

    Dame, T. M.

    1984-01-01

    Galactic CO line emission at 115 GHz was surveyed in order to study the distribution of molecular clouds in the inner galaxy. Comparison of this survey with similar H1 data reveals a detailed correlation with the most intense 21 cm features. To each of the classical 21 cm H1 spiral arms of the inner galaxy there corresponds a CO molecular arm which is generally more clearly defined and of higher contrast. A simple model is devised for the galactic distribution of molecular clouds. The modeling results suggest that molecular clouds are essentially transient objects, existing for 15 to 40 million years after their formation in a spiral arm, and are largely confined to spiral features about 300 pc wide.

  20. Galactic kinematics derived from classical cepheids

    NASA Astrophysics Data System (ADS)

    Zhu, Zi

    On the basis of radial velocity and Hipparcos proper motion data, we have analyzed the galactic kinematics of classical Cepheids. Using the 3-D Ogorodnikov-Milne model we have determined the rotational velocity of the Galaxy to be V0 = 240.5 ± 10.2 km/s, on assuming a glactocentric distance of the Sun of R0 = 8.5 kpc. The results clearly indicate a contracting motion in the solar neighbourhood of (∂V θ∂θ)/R = -2.60 ± 1.07 km s -1 kpc -1, along the direction of galactic rotation. Possible reason for this motion is discussed. The solar motion found here is S⊙ = 18.78 ± 0.86 km/s in the direction l⊙ = 54.4° ± 2.9° and b⊙ = +26.6° ± 2.6°.

  1. Detailed Abundance Analysis of a Metal-poor Giant in the Galactic Center

    NASA Astrophysics Data System (ADS)

    Ryde, N.; Fritz, T. K.; Rich, R. M.; Thorsbro, B.; Schultheis, M.; Origlia, L.; Chatzopoulos, S.

    2016-11-01

    We report the first results from our program to examine the metallicity distribution of the Milky Way nuclear star cluster connected to Sgr A*, with the goal of inferring the star formation and enrichment history of this system, as well as its connection and relationship with the central 100 pc of the bulge/bar system. We present the first high-resolution (R ∼ 24,000), detailed abundance analysis of a K = 10.2 metal-poor, alpha-enhanced red giant projected at 1.5 pc from the Galactic center, using NIRSPEC on Keck II. A careful analysis of the dynamics and color of the star locates it at about {26}-16+54 pc line-of-sight distance in front of the nuclear cluster. It probably belongs to one of the nuclear components (cluster or disk), not to the bar/bulge or classical disk. A detailed spectroscopic synthesis, using a new line list in the K band, finds [Fe/H] ∼ ‑1.0 and [α/Fe] ∼ +0.4, consistent with stars of similar metallicity in the bulge. As known giants with comparable [Fe/H] and alpha enhancement are old, we conclude that this star is most likely to be a representative of the ∼10 Gyr old population. This is also the most metal-poor-confirmed red giant yet discovered in the vicinity of the nuclear cluster of the Galactic center. We consider recent reports in the literature of a surprisingly large number of metal-poor giants in the Galactic center, but the reported gravity of {log}g∼ 4 for these stars calls into question their reported metallicities.

  2. Accretion disk thermal instability in galactic nuclei

    NASA Astrophysics Data System (ADS)

    Mineshige, S.; Shields, G. A.

    1990-03-01

    The nonlinear evolution and spatial propagation of the thermal instability in accretion disks in galactic nuclei are investigated. Integrations of the vertical structure of the disks are described for different alpha prescriptions, and the thermal stability is examined. Global time-dependent calculations of the unstable disks are performed which show that there are two distinct types of behavior according to the assumed prescription for the viscosity parameter: the 'purr' type and the 'roar' type. The roar type is analyzed in some detail.

  3. A cool disk in the Galactic Center?

    NASA Astrophysics Data System (ADS)

    Liu, B. F.; Meyer, F.; Meyer-Hofmeister, E.

    2004-07-01

    We study the possibility of a cool disk existing in the Galactic Center in the framework of the disk-corona evaporation/condensation model. Assuming an inactive disk near the gravitational capture distance left over from an earlier evolutionary stage, a hot corona should form above the disk since there is a continuous supply of hot gas from stellar winds of the close-by massive stars. We study the interaction between the disk and the corona. Whether the cool disk can survive depends on the mass exchange between disk and corona which is determined by the energy and pressure balance. If evaporation is the dominant process and the rate is larger than the Bondi accretion rate in the Galactic Center, the disk will be depleted within a certain time and no persistent disk will exist. On the other hand, if the interaction results in hot gas steadily condensing into the disk, an inactive cool disk with little gas accreting towards the central black hole might survive in the Galactic Center. For this case we further investigate the Bremsstrahlung radiation from the hot corona and compare it with the observed X-ray luminosity. Our model shows that, for standard viscosity in the corona (α=0.3), the mass evaporation rate is much higher than the Bondi accretion rate and the coronal density is much larger than that inferred from Chandra observations. An inactive disk can not survive such strong evaporation. For small viscosity (α ⪉ 0.07) we find condensation solutions. But detailed coronal structure computations show that in this case there is too much X-ray radiation from the corona to be in agreement with the observations. From this modeling we conclude that there should be no thin/inactive disk presently in the Galactic Center. However we do not exclude that the alternative non-radiative model of Nayakshin (\\cite{Nayakshin04}) might instead be realized in nature and shortly discuss this question.}

  4. Cold GMC cores in the Galactic Centre

    NASA Astrophysics Data System (ADS)

    Lis, D. C.; Li, Y.; Dowell, C. D.; Menten, K. M.

    1999-03-01

    We have used the Long Wavelength Spectrometer (LWS) aboard the Infrared Space Observatory in grating mode to map the far-infrared continuum emission (45-175 mic) toward several massive Giant Molecular Cloud (GMC) cores located near the Galactic center. These sources are observed in emission at far-infrared and submillimeter wavelengths (>100 mic). However, at mid-infrared wavelengths (<70 mic) they are seen in absorption against the general Galactic centre background. Gray-body fits to the observed far-infrared and submillimeter spectral energy distributions give low temperatures (about 13-20 K) for the bulk of the dust in all the sources. This indicates external heating of the dust by the diffuse ISRF and suggests that the cores do not harbor high-mass star-formation sites, in spite of their large molecular mass. In addition, the grain emissivity in these sources is a very steep function of frequency (β > 2.4). The high grain emissivity exponent is consistent with the presence of dust grains covered with thick ice mantles. Molecular line observations carried out with the Caltech Submillimeter Observatory (CSO) show a large velocity gradient across the most massive core, GCM0.25+0.11, indicative of streaming motions of the gas or of the presence of multiple, spatially overlapping velocity components. The observed gas kinematics may indicate that the GCM0.25+0.11 core is in an early stage of a cloud-cloud collision that may result in a future star formation episode. Recent MSX observations indicate that cold GMC cores similar to those studied with ISO are ubiquitous in the Galactic center and throughout the Galaxy. The observed intensities of the OI and CII fine structure lines imply a radiation field intensity of about 1000 times the standard ISRF intensity and a hydrogen density of about 1000 pccm\\ for the diffuse gas component in the Galactic center.

  5. Understanding active galactic nuclei: peeling the onion.

    NASA Astrophysics Data System (ADS)

    Krolik, J. H.

    A brief review is presented of selected current problems in understanding active galactic nuclei, with special emphasis on the contributions that X-ray observations can make. Questions having to do with: how the character of the host galaxy influences nuclear activity; emission line regions; the border between the nucleus and the stellar portion of the active galaxy; radiation of the nonthermal continuum; and the possible existence of an accretion disk are touched upon.

  6. Galactic Cosmic Rays: From Earth to Sources

    NASA Technical Reports Server (NTRS)

    Brandt, Theresa J.

    2012-01-01

    For nearly 100 years we have known that cosmic rays come from outer space, yet proof of their origin, as well as a comprehensive understanding of their acceleration, remains elusive. Direct detection of high energy (up to 10(exp 15)eV), charged nuclei with experiments such as the balloon-born, antarctic Trans-Iron Galactic Element Recorder (TIGER) have provided insight into these mysteries through measurements of cosmic ray abundances. The abundance of these rare elements with respect to certain intrinsic properties suggests that cosmic rays include a component of massive star ejecta. Supernovae and their remnants (SNe & SNRs), often occurring at the end of a massive star's life or in an environment including massive star material, are one of the most likely candidates for sources accelerating galactic comic ray nuclei up to the requisite high energies. The Fermi Gamma-ray Space Telescope Large Area Detector (Fermi LAT) has improved our understanding of such sources by widening the window of observable energies and thus into potential sources' energetic processes. In combination with multiwavelength observations, we are now better able to constrain particle populations (often hadron-dominated at GeV energies) and environmental conditions, such as the magnetic field strength. The SNR CTB 37A is one such source which could contribute to the observed galactic cosmic rays. By assembling populations of SNRs, we will be able to more definitively define their contribution to the observed galactic cosmic rays, as well as better understand SNRs themselves. Such multimessenger studies will thus illuminate the long-standing cosmic ray mysteries, shedding light on potential sources, acceleration mechanisms, and cosmic ray propagation.

  7. Gamma rays from active galactic nuclei

    NASA Technical Reports Server (NTRS)

    Kazanas, Demosthenes

    1990-01-01

    The general properties of Active Galactic Nuclei (AGN) and quasars are reviewed with emphasis on their continuum spectral emission. Two general classes of models for the continuum are outlined and critically reviewed in view of the impending GRO (Gamma Ray Observatory) launch and observations. The importance of GRO in distinguishing between these models and in general in furthering the understanding of AGN is discussed. The very broad terms the status of the current understanding of AGN are discussed.

  8. The age of the galactic disk

    NASA Technical Reports Server (NTRS)

    Sandage, Allan

    1988-01-01

    The galactic disk is a dissipative structure and must, therefore be younger than the halo if galaxy formation generally proceeds by collapse. Just how much younger the oldest stars in the galactic disk are than the oldest halo stars remains an open question. A fast collapse (on a time scale no longer than the rotation period of the extended protogalaxy) permits an age gap of the order of approximately 10 to the 9th power years. A slow collapse, governed by the cooling rate of the partially pressure supported falling gas that formed into what is now the thick stellar disk, permits a longer age gap, claimed by some to be as long as 6 Gyr. Early methods of age dating the oldest components of the disk contain implicit assumptions concerning the details of the age-metallicity relation for stars in the solar neighborhood. The discovery that this relation for open clusters outside the solar circle is different that in the solar neighborhood (Geisler 1987), complicates the earlier arguments. The oldest stars in the galactic disk are at least as old as NGC 188. The new data by Janes on NGC 6791, shown first at this conference, suggest a disk age of at least 12.5 Gyr, as do data near the main sequence termination point of metal rich, high proper motion stars of low orbital eccentricity. Hence, a case can still be made that the oldest part of the galactic thick disk is similar in age to the halo globular clusters, if their ages are the same as 47 Tuc.

  9. Chemical Abundance Analysis of the Symbiotic Red Giants

    NASA Astrophysics Data System (ADS)

    Galan, Cezary; Mikolajewska, Joanna; Hinkle, Kenneth H.

    2015-01-01

    The study of symbiotic stars - the long period, interacting binary systems - composed of red giant donor and a hot, compact companion is important for our understanding of binary stellar evolution in systems where mass loss or transfer take place involving RGB/AGB stars. The elemental abundances of symbiotic giants can track the mass exchange history and can determine their parent stellar population. However, the number of these objects with fairly well determined photospheric composition is insufficient for statistical considerations. Here we present the detailed chemical abundance analysis obtained for the first time for 14 M-type symbiotic giants. The analysis is based on the high resolution (R ˜ 50000), high S/N ˜ 100, near-IR spectra (at H- and K-band regions) obtained with Phoenix/Gemini South spectrometer. Spectrum synthesis employing standard LTE analysis and atmosphere models was used to obtain photospheric abundances of CNO and elements around the iron peak (Sc, Ti, Fe, and Ni). Our analysis reveals mostly slightly sub-solar or near-solar metallicities. We obtained significantly subsolar metallicities for RW Hya, RT Ser, and Hen 3-1213 and slightly super-solar metallicity in V455 Sco. The very low ^{12}C/^{13}C isotopic ratios, ˜6-11, and significant enrichment in nitrogen ^{14}N isotope in almost all giants in our sample indicate that they have experienced the first dredge-up.

  10. Galactic worms. I - Catalog of worm candidates

    NASA Technical Reports Server (NTRS)

    Koo, Bon-Chul; Heiles, Carl; Reach, William T.

    1992-01-01

    A catalog of candidates for the Galactic worms that are possibly the walls surrounding the superbubbles is compiled; 118 isolated structures that appear both in H I and in IR (60 and 100 microns). Fifty-two are possibly associated with H II regions. It is found that the 100-micron emissivity increases systematically toward the Galactic interior, which is consistent with the increase of the general interstellar radiation field. The 100-micron emissivity of the structures associated with the H II regions is larger than that of the structures without associated H II regions. The 60-100-micron ratio is large, 0.28 +/- 0.03, which may indicate that the grains associated with the atomic gas have a relatively large population of small grains. Thirty-five structures appear in the 408-MHz continuum. The IR and the radio continuum properties suggest that the 408-MHz continuum emission in those structures is very likely thermal. The implications of these results on the ionization of gas far from the Galactic plane are discussed.

  11. HEAO 1 measurements of the galactic ridge

    NASA Technical Reports Server (NTRS)

    Worrall, D. M.; Marshall, F. E.; Boldt, E. A.; Swank, J. H.

    1981-01-01

    The HEAO A2 experiment data was systematically searched for unresolved galactic disc emission. Although there were suggestions of non-uniformities in the emission, the data were consistent with a disc of half-thickness 241 + 22 pc and surface emissivity (2-10 keV) at galactic radius R(kpc) of 2.2 10 to the minus 7th power exp(-R/3.5) erg/sq cm to the (-2)power/s (R 7.8 kpc). giving a luminosity of approximately 4.4 10 to the 37th power erg S to the (-1) power. If the model is extrapolated to radii less than 7.8 kpc, the unresolved disc emission is approximately 1.4 10 to the 38th power erg S to the (-1) power (2-10 keV) i.e., a few percent of the luminosity of the galaxy in resolved sources. the disc emission has a spectrum which is significantly softer than that of the high galactic latitude diffuse X-ray background and it is most probably of discrete source origin.

  12. On the physical origin of galactic conformity

    NASA Astrophysics Data System (ADS)

    Hearin, Andrew P.; Behroozi, Peter S.; van den Bosch, Frank C.

    2016-09-01

    Correlations between the star formation rates (SFRs) of nearby galaxies (so-called galactic conformity) have been observed for projected separations up to 4 Mpc, an effect not predicted by current semi-analytic models. We investigate correlations between the mass accretion rates (dMvir/dt) of nearby haloes as a potential physical origin for this effect. We find that pairs of host haloes `know about' each others' assembly histories even when their present-day separation is greater than thirty times the virial radius of either halo. These distances are far too large for direct interaction between the haloes to explain the correlation in their dMvir/dt. Instead, halo pairs at these distances reside in the same large-scale tidal environment, which regulates dMvir/dt for both haloes. Larger haloes are less affected by external forces, which naturally gives rise to a mass dependence of the halo conformity signal. SDSS measurements of galactic conformity exhibit a qualitatively similar dependence on stellar mass, including how the signal varies with distance. Based on the expectation that halo accretion and galaxy SFR are correlated, we predict the scale-, mass- and redshift-dependence of large-scale galactic conformity, finding that the signal should drop to undetectable levels by z ≳ 1. These predictions are testable with current surveys to z ˜ 1; confirmation would establish a strong correlation between dark matter halo accretion rate and central galaxy SFR.

  13. The Making of a Galactic Parallelogram

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This image taken by NASA's Spitzer Space Telescope shows in unprecedented detail the galaxy Centaurus A's last big meal: a spiral galaxy seemingly twisted into a parallelogram-shaped structure of dust. Spitzer's ability to both see dust and see through it allowed the telescope to peer into the center of Centaurus A and capture this galactic remnant as never before.

    An elliptical galaxy located 11 million light-years from Earth, Centaurus A is one of the brightest sources of radio waves in the sky. These radio waves indicate the presence of a supermassive black hole, which may be 'feeding' off the leftover galactic meal.

    A high-speed jet of gas can be seen shooting above the plane of the galaxy (the faint, fuzzy feature pointing from the center toward the upper left). Jets are a common feature of galaxies, and this one is probably receiving an extra boost from the galactic remnant.

    Scientists have created a model that explains how such a strangely geometric structure could arise. In this model, a spiral galaxy falls into an elliptical galaxy, becoming warped and twisted in the process. The folds in the warped disc create the parallelogram-shaped illusion.

  14. Galactic civilizations - Population dynamics and interstellar diffusion

    NASA Technical Reports Server (NTRS)

    Newman, W. I.; Sagan, C.

    1981-01-01

    A model is developed of the interstellar diffusion of galactic civilizations which takes into account the population dynamics of such civilizations. The problem is formulated in terms of potential theory, with a family of nonlinear partial differential and difference equations specifying population growth and diffusion for an organism with advantageous genes that undergoes random dispersal while increasing in population locally, and a population at zero population growth. In the case of nonlinear diffusion with growth and saturation, it is found that the colonization wavefront from the nearest independently arisen galactic civilization can have reached the earth only if its lifetime exceeds 2.6 million years, or 20 million years if discretization can be neglected. For zero population growth, the corresponding lifetime is 13 billion years. It is concluded that the earth is uncolonized not because interstellar spacefaring civilizations are rare, but because there are too many worlds to be colonized in the plausible colonization lifetime of nearby civilizations, and that there exist no very old galactic civilizations with a consistent policy of the conquest of inhabited worlds.

  15. Vertical Shear of the Galactic Interstellar Medium

    NASA Astrophysics Data System (ADS)

    Benjamin, R. A.

    2000-05-01

    The detection of UV absorption, 21 cm, Hα and other diffuse optical emission lines from gas up to ten kiloparsecs above the plane of the Milky Way and other galaxies provides the first opportunity to probe the rotational properties of the ionized ``atmospheres'' of galaxies. This rotation has implications for our understanding of the Galactic gravitational potential, angular momentum transport in the Galactic disk, and the maintenance of a Galactic dynamo. The available evidence indicates that gas rotates nearly cylindrically up to a few kiloparsecs. This is in contrast to the expectation that there should be a significant gradient in rotation speed as a function of height assuming a reasonable mass model for the Galaxy. For example, for a vertical cut at galactocentric radius R= 5 kpc in NGC 891 by Rand, the rotation speed is observed to drop by ~ 30 km s-1 from z=1 to 5 kpc and is expected to drop by 80 km s-1. Magnetic tension forces may resolve this discrepancy. Other possiblilities will be examined in the near future.

  16. Galactic constraints on supernova progenitor models

    NASA Astrophysics Data System (ADS)

    Acharova, I. A.; Gibson, B. K.; Mishurov, Yu. N.; Kovtyukh, V. V.

    2013-09-01

    Aims: To estimate the mean masses of oxygen and iron ejected per each type of supernovae (SNe) event from observations of the elemental abundance patterns in the Galactic disk and constrain the relevant SNe progenitor models. Methods: We undertake a statistical analysis of the radial abundance distributions in the Galactic disk within a theoretical framework for Galactic chemical evolution which incorporates the influence of spiral arms. This framework has been shown to recover the non-linear behaviour in radial gradients, the mean masses of oxygen and iron ejected during SNe explosions to be estimated, and constraints to be placed on SNe progenitor models. Results: (i) The mean mass of oxygen ejected per core-collapse SNe (CC SNe) event (which are concentrated within spiral arms) is ~0.27 M⊙; (ii) the mean mass of iron ejected by tardy Type Ia SNe (SNeIa, whose progenitors are older/longer-lived stars with ages ≳100 Myr and up to several Gyr, which do not concentrate within spiral arms) is ~0.58 M⊙; (iii) the upper mass of iron ejected by prompt SNeIa (SNe whose progenitors are younger/shorter-lived stars with ages ≲100 Myr, which are concentrated within spiral arms) is ≤0.23 M⊙ per event; (iv) the corresponding mean mass of iron produced by CC SNe is ≤0.04 M⊙ per event; (v) short-lived SNe (core-collapse or prompt SNeIa) supply ~85% of the Galactic disk's iron. Conclusions: The inferred low mean mass of oxygen ejected per CC SNe event implies a low upper mass limit for the corresponding progenitors of ~23 M⊙, otherwise the Galactic disk would be overabundant in oxygen. This inference is the consequence of the non-linear dependence between the upper limit of the progenitor initial mass and the mean mass of oxygen ejected per CC SNe explosion. The low mean mass of iron ejected by prompt SNeIa, relative to the mass produced by tardy SNeIa (~2.5 times lower), prejudices the idea that both sub-populations of SNeIa have the same physical nature. We

  17. Calculating Method and Characteristics of the Distribution of Neutron Exposures in Radiative S-process Nucleosynthesis Model for AGB Stars

    NASA Astrophysics Data System (ADS)

    Zhang, F. H.; Zhou, G. D.; Cui, W. Y.; Zhang, B.

    2013-01-01

    An investigation on the distribution of neutron exposuresin the low-mass asymptotic giant branch (AGB) stars is presented, according to the s-process nucleosynthesis model with the (^{12}C(α,n)^{16}O) reaction occurring under radiative conditions in the interpulse phases. The model parameters, such as the fractional overlap of two successive convective thermal pulses (r), the mass fraction of (^{13}C) pocket in the He intershell (q), and the mass of the effective (^{13}C) in the (^{13}C) pocket, vary with pulse number. Considering these factors, the calculating method for the distribution of neutron exposures in the He intershell is presented. This method has the characteristics of simplicity and universality. Using this method, the exposure distributions of the stellar model for a star with a mass of (3 {M_⊙}) and solar metallicity are calculated. The results suggest that, with the reasonable assumption that the (^{13}C) pocket has a uniform composition, the final exposure distribution can still be approximated by an exponential law. For a stellar model with a fixed initial mass and metallicity, there is a definite relation between the mean neutron exposure ({τ_0}), and the neutron exposure (Δτ) for per interpulse. That is ({τ_0} = 0.434λ({q_{1,}}{q_2} … {q_{{m_{max}} + 1}},{r_{1,}}{r_2} … {r_{{m_{max}} + 1}})Δτ), where ({m_{max}}) is the total number of thermal pulses with the third dredge-up episode, and the proportional coefficient (λ({q_{1,}}{q_2} … {q_{{m_{max}} + 1}},{r_{1,}}{r_2} … {r_{{m_{max}} + 1}})) can be determined through an exponential curve fitting to the final exposure distribution. This new formula quantitatively unifies the classical model with the stellar model in terms of the distribution of neutron exposures, and makes the classical model continue to offer guidance and constraints to the s-process numerical calculations in stellar models.

  18. 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.

  19. The Stellar Population Structure of the Galactic Disk

    NASA Astrophysics Data System (ADS)

    Bovy, Jo; Rix, Hans-Walter; Schlafly, Edward F.; Nidever, David L.; Holtzman, Jon A.; Shetrone, Matthew; Beers, Timothy C.

    2016-05-01

    The spatial structure of stellar populations with different chemical abundances in the Milky Way (MW) contains a wealth of information on Galactic evolution over cosmic time. We use data on 14,699 red-clump stars from the APOGEE survey, covering 4 {kpc}≲ R≲ 15 {kpc}, to determine the structure of mono-abundance populations (MAPs)—stars in narrow bins in [α /{Fe}] and [{Fe}/{{H}}]—accounting for the complex effects of the APOGEE selection function and the spatially variable dust obscuration. We determine that all MAPs with enhanced [α /{Fe}] are centrally concentrated and are well-described as exponentials with a scale length of 2.2+/- 0.2 {kpc} over the whole radial range of the disk. We discover that the surface-density profiles of low-[α /{Fe}] MAPs are complex: they do not monotonically decrease outwards, but rather display a peak radius ranging from ≈ 5 to ≈ 13 {kpc} at low [{Fe}/{{H}}]. The extensive radial coverage of the data allows us to measure radial trends in the thickness of each MAP. While high-[α /{Fe}] MAPs have constant scale heights, low-[α /{Fe}] MAPs flare. We confirm, now with high-precision abundances, previous results that each MAP contains only a single vertical scale height and that low-[{Fe}/{{H}}], low-[α /{Fe}] and high-[{Fe}/{{H}}], high-[α /{Fe}] MAPs have intermediate ({h}Z≈ 300{--}600 {pc}) scale heights that smoothly bridge the traditional thin- and thick-disk divide. That the high-[α /{Fe}], thick disk components do not flare is strong evidence against their thickness being caused by radial migration. The correspondence between the radial structure and chemical-enrichment age of stellar populations is clear confirmation of the inside-out growth of galactic disks. The details of these relations will constrain the variety of physical conditions under which stars form throughout the MW disk.

  20. Compact planetary nebulae in the Galactic disk: Analysis of the central stars

    NASA Astrophysics Data System (ADS)

    Moreno-Ibáñez, Manuel; Villaver, Eva; Shaw, Richard A.; Stanghellini, Letizia

    2016-09-01

    Context. We have obtained multi-wavelength observations of compact Galactic planetary nebulae (PNe) to probe post-asymptotic giant branch (AGB) evolution from the onset of nebular ejection. Here we analyze new observations from HST to derive the masses and evolutionary status of their central stars (CSs). Aims: Our objective here is to derive the masses of the CSs hosted by compact PNe in order to better understand the relationship between the CS properties and those of the surrounding nebulae. We also compare this sample with others we obtained using the same technique in different metallicity environments: the Large and Small Magellanic Clouds. Methods: This paper is based on HST/WFC3 images of 51 targets obtained in a snapshot survey (GO-11657). The high spatial resolution of HST allows us to resolve these compact PNe and distinguish the CS emission from that of their surrounding PNe. We derive CS bolometric luminosities and effective temperatures using the Zanstra technique, from a combination of HST photometry and ground-based spectroscopic data. The targets were imaged through the filters F200LP, F350LP, and F814W from which we derive Johnson V and I magnitudes. We infer CS masses by placing the stars on a temperature-luminosity diagram and compare their location with the best available, single star post-AGB evolutionary tracks. Results: We present new, unique photometric measurements of 50 CSs, and we derive effective temperatures and luminosities for most of them. Central star masses for 23 targets were derived with the evolutionary track technique; the remaining masses were indeterminate most likely because of underestimates of the stellar temperature, or because of substantial errors in the adopted statistical distances to these objects. We expect these problems will be largely overcome when the Gaia distance catalog becomes available. We find that objects with the higher ratios of Zanstra temperatures T(H i)/T( He ii ) tend to have lower-mass progenitors

  1. SAS-2 galactic gamma-ray results. 1: Diffuse emission

    NASA Technical Reports Server (NTRS)

    Thompson, D. J.; Fichtel, C. E.; Hartman, R. C.; Kniffen, D. A.; Bignami, G. F.; Lamb, R. C.; Oegelman, H.; Oezel, M. E.; Tuemer, T.

    1977-01-01

    Continuing analysis of the data from the SAS-2 high energy gamma ray experiment has produced an improved picture of the sky at photon energies above 35 MeV. On a large scale, the diffuse emission from the galactic plane is the dominant feature observed by SAS-2. This galactic plane emission is most intense between galactic longitudes 310 deg and 45 deg, corresponding to a region within 7 kpc of the galactic center. Within the high-intensity region, SAS-2 observes peaks around galactic longitudes 315, 330, 345, 0, and 35 deg. These peaks appear to be correlated with galactic features and components such as molecular hydrogen, atomic hydrogen, magnetic fields, cosmic-ray concentrations, and photon fields.

  2. 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.

  3. NEW DETERMINATION OF THE {sup 13}C({alpha}, n){sup 16}O REACTION RATE AND ITS INFLUENCE ON THE s-PROCESS NUCLEOSYNTHESIS IN AGB STARS

    SciTech Connect

    Guo, B.; Li, Z. H.; Li, Y. J.; Su, J.; Yan, S. Q.; Bai, X. X.; Chen, Y. S.; Fan, Q. W.; Jin, S. J.; Li, E. T.; Li, Z. C.; Lian, G.; Liu, J. C.; Liu, X.; Shu, N. C.; Lugaro, M.; Buntain, J.; Pang, D. Y.; Karakas, A. I.; Shi, J. R. E-mail: guobing@ciae.ac.cn; and others

    2012-09-10

    We present a new measurement of the {alpha}-spectroscopic factor (S{sub {alpha}}) and the asymptotic normalization coefficient for the 6.356 MeV 1/2{sup +} subthreshold state of {sup 17}O through the {sup 13}C({sup 11}B, {sup 7}Li){sup 17}O transfer reaction and we determine the {alpha}-width of this state. This is believed to have a strong effect on the rate of the {sup 13}C({alpha}, n){sup 16}O 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 {sup 13}C({alpha}, n){sup 16}O reaction. At a temperature of 100 MK, our rate is roughly two times larger than that by Caughlan and 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 {sup 13}C({alpha}, n){sup 16}O reaction when the {sup 13}C burns completely in radiative conditions. When the {sup 13}C burns in convective conditions, as in stars of initial mass lower than {approx}2 M{sub Sun} 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. 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.

  5. Planetary nebulae near the Galactic Centre: chemical abundances

    NASA Astrophysics Data System (ADS)

    Cavichia, O.; Costa, R. D. D.; Maciel, W. J.; Mollá, M.

    2014-10-01

    In this work, we report physical parameters and abundances derived for a sample of high extinction planetary nebulae located in the Galactic bulge, near the Galactic Centre, based on low dispersion spectroscopy secured at the SOAR telescope using the Goodman spectrograph. The results show that the abundances of our sample are similar to those from other regions of the bulge. Nevertheless, the average abundances of the Galactic bulge do not follow the observed trend of the radial abundance gradient in the disk.

  6. Nanoparticles in the Red Rectangle: A Challenge to Laboratory Astrophysics

    NASA Astrophysics Data System (ADS)

    Witt, A. N.; Vijh, U. P.

    2005-05-01

    The Red Rectangle (RR) is a biconical proto-planetary nebula, produced by the post-AGB star system HD 44179. The system is currently in a dust/molecule producing phase and is exhibiting evidence of mixed C-rich/O-rich chemistries. The central binary source is hidden by an optically thick equatorial disk seen edge-on, which permits the direct observation of nebular emissions without undue interference from direct stellar radiation. A small fraction of residual star light emerges from the central region of the nebula only after having suffered substantial degrees of scattering and absorption by the nebular material. Thus, the absorption characteristics of the nebular dust can be studied as well. In addition to the well-documented extended red emission (ERE) band (540 - 800 nm) that gives the RR its distinctive color and morphology, the optical spectrum of the RR also exhibits a blue luminescence (BL) component, with peak emission near a wavelength of 380 nm. We will discuss the spectra and spatial morphologies of these emissions. If both emission bands are produced by the same family of emitters, their spatial preference for mutually exclusive environments suggest that they relate to different ionization stages. We will present observational data and comparisons with laboratory data that suggest that the BL may be the result of fluorescence by small, neutral PAH molecules with three to four carbon rings that exist preferentially in the shadow of the disk. The different excitation conditions for the ERE suggest the possible involvement of PAH dications. Laboratory data on the electronic spectra of PAH dications and their fluorescence properties are urgently needed. We gratefully acknowledge support from NSF Grant AST 0307307 which has made this research possible.

  7. Red Bull Stratos Presentation

    NASA Video Gallery

    Red Bull Stratos High Performance Director Andy Walshe & Technical Project Director Art Thompson share the Stratos story with JSC. Supported by a team of experts, Felix Baumgartner reached 128,100 ...

  8. Starburst clusters in the Galactic center

    NASA Astrophysics Data System (ADS)

    Habibi, Maryam

    2014-09-01

    The central region of the Galaxy is the most active site of star formation in the Milky Way, where massive stars have formed very recently and are still forming today. The rich population of massive stars in the Galactic center provide a unique opportunity to study massive stars in their birth environment and probe their initial mass function, which is the spectrum of stellar masses at their birth. The Arches cluster is the youngest among the three massive clusters in the Galactic center, providing a collection of high-mass stars and a very dense core which makes this cluster an excellent site to address questions about massive star formation, the stellar mass function and the dynamical evolution of massive clusters in the Galactic center. In this thesis, I perform an observational study of the Arches cluster using K_{s}-band imaging obtained with NAOS/CONICA at the VLT combined with Subaru/Cisco J-band data to gain a full understanding of the cluster mass distribution out to its tidal radius for the first time. Since the light from the Galactic center reaches us through the Galactic disc, the extinction correction is crucial when studying this region. I use a Bayesian method to construct a realistic extinction map of the cluster. It is shown in this study that the determination of the mass of the most massive star in the Arches cluster, which had been used in previous studies to establish an upper mass limit for the star formation process in the Milky Way, strongly depends on the assumed slope of the extinction law. Assuming the two regimes of widely used infrared extinction laws, I show that the difference can reach up to 30% for individually derived stellar masses and Δ A_{Ks}˜ 1 magnitude in acquired K_{s}-band extinction, while the present-day mass function slope changes by ˜ 0.17 dex. The present-day mass function slope derived assuming the more recent extinction law, which suggests a steeper wavelength dependence for the infrared extinction law, reveals

  9. The Apache Point Observatory Galactic Evolution Experiment (APOGEE) in Sloan Digital Sky Survey III (SDSS-III)

    NASA Astrophysics Data System (ADS)

    Majewski, Steven R.; Wilson, John C.; Hearty, Fred; Schiavon, Ricardo R.; Skrutskie, Michael F.

    2010-03-01

    The Apache Point Observatory Galactic Evolution Experiment (APOGEE) is a large-scale, near-infrared (H-band), high-resolution (R ~ 30,000), high S/N (≳100) spectroscopic survey of Milky Way stellar populations. APOGEE will operate from 1.51-1.68μm, a region that includes useful absorption lines from at least fifteen chemical species including α, odd-Z, and iron peak elements. The APOGEE instrument has a novel design featuring 300 science fibers feeding light to a mosaiced VPH grating and a six-element camera encased in a liquid nitrogen-cooled cryostat. A three year bright-time observing campaign will enable APOGEE to observe approximately 100,000 red giants across the Galactic bulge, disk and halo.

  10. Gamma ray constraints on the galactic supernova rate

    NASA Technical Reports Server (NTRS)

    Hartmann, D.; The, L.-S.; Clayton, D. D.; Leising, M.; Mathews, G.; Woosley, S. E.

    1992-01-01

    Monte Carlo simulations of the expected gamma-ray signatures of galactic supernovae of all types are performed in order to estimate the significance of the lack of a gamma-ray signal due to supernovae occurring during the last millenium. Using recent estimates of nuclear yields, we determine galactic supernova rates consistent with the historic supernova record and the gamma-ray limits. Another objective of these calculations of galactic supernova histories is their application to surveys of diffuse galactic gamma-ray line emission.

  11. Whence the red panda?

    PubMed

    Flynn, J J; Nedbal, M A; Dragoo, J W; Honeycutt, R L

    2000-11-01

    The evolutionary history of the red panda (Ailurus fulgens) plays a pivotal role in the higher-level phylogeny of the "bear-like" arctoid carnivoran mammals. Characters from morphology and molecules have provided inconsistent evidence for placement of the red panda. Whereas it certainly is an arctoid, there has been major controversy about whether it should be placed with the bears (ursids), ursids plus pinnipeds (seals, sea lions, walrus), raccoons (procyonids), musteloids (raccoons plus weasels, skunks, otters, and badgers [mustelids]), or as a monotypic lineage of uncertain phylogenetic affinities. Nucleotide sequence data from three mitochondrial genes and one nuclear intron were analyzed, with more complete taxonomic sampling of relevant taxa (arctoids) than previously available in analyses of primary molecular data, to clarify the phylogenetic relationships of the red panda to other arctoid carnivorans. This study provides detailed phylogenetic analyses (both parsimony and maximum-likelihood) of primary character data for arctoid carnivorans, including bootstrap and decay indices for all arctoid nodes, and three statistical tests of alternative phylogenetic hypotheses for the placement of the red panda. Combined phylogenetic analyses reject the hypotheses that the red panda is most closely related to the bears (ursids) or to the raccoons (procyonids). Rather, evidence from nucleotide sequences strongly support placement of the red panda within a broad Musteloidea (sensu lato) clade, including three major lineages (the red panda, the skunks [mephitids], and a clearly monophyletic clade of procyonids plus mustelids [sensu stricto, excluding skunks]). Within the Musteloidea, interrelationships of the three major lineages are unclear and probably are best considered an unresolved trichotomy. These data provide compelling evidence for the relationships of the red panda and demonstrate that small taxonomic sample sizes can result in misleading or possibly erroneous

  12. Whence the red panda?

    PubMed

    Flynn, J J; Nedbal, M A; Dragoo, J W; Honeycutt, R L

    2000-11-01

    The evolutionary history of the red panda (Ailurus fulgens) plays a pivotal role in the higher-level phylogeny of the "bear-like" arctoid carnivoran mammals. Characters from morphology and molecules have provided inconsistent evidence for placement of the red panda. Whereas it certainly is an arctoid, there has been major controversy about whether it should be placed with the bears (ursids), ursids plus pinnipeds (seals, sea lions, walrus), raccoons (procyonids), musteloids (raccoons plus weasels, skunks, otters, and badgers [mustelids]), or as a monotypic lineage of uncertain phylogenetic affinities. Nucleotide sequence data from three mitochondrial genes and one nuclear intron were analyzed, with more complete taxonomic sampling of relevant taxa (arctoids) than previously available in analyses of primary molecular data, to clarify the phylogenetic relationships of the red panda to other arctoid carnivorans. This study provides detailed phylogenetic analyses (both parsimony and maximum-likelihood) of primary character data for arctoid carnivorans, including bootstrap and decay indices for all arctoid nodes, and three statistical tests of alternative phylogenetic hypotheses for the placement of the red panda. Combined phylogenetic analyses reject the hypotheses that the red panda is most closely related to the bears (ursids) or to the raccoons (procyonids). Rather, evidence from nucleotide sequences strongly support placement of the red panda within a broad Musteloidea (sensu lato) clade, including three major lineages (the red panda, the skunks [mephitids], and a clearly monophyletic clade of procyonids plus mustelids [sensu stricto, excluding skunks]). Within the Musteloidea, interrelationships of the three major lineages are unclear and probably are best considered an unresolved trichotomy. These data provide compelling evidence for the relationships of the red panda and demonstrate that small taxonomic sample sizes can result in misleading or possibly erroneous

  13. Red cell metabolism in red and grey kangaroos.

    PubMed

    Agar, N S

    1977-12-15

    Glucose utilization, lactate production and glutathione regeneration were measured in the red blood cells of 2 species of Australian Marsupials, Eastern grey Kangaroo (Macropus gigantus) and red kangaroo (Macropus rufus), and were found to be significantly lower in the red blood cells from grey than that of red kangaroos.

  14. Infrared studies of galactic center x-ray sources

    NASA Astrophysics Data System (ADS)

    DeWitt, Curtis

    -type supergiant at an distance of 3.7 kpc; and an O star at the Galactic Center distance. I also identified 3 foreground X-ray source counterparts within a distance of 1 kpc which do not show obvious emission features in their spectra. However, on the basis of the low surface density of unreddened sources along the line-of-sight to the Galactic Center and our previous statistical analysis (DeWitt et al., 2010), these can be securely identified as the true counterparts to their coincident X-ray point sources. Lastly, I used the results of my matching simulations to infer the presence of 7+/-2 true counterparts within a set of late type giants that I observed without detectable emission features. I conclude from this work that the probable excess in red giant X-ray counterparts without emission lines needs to be confirmed both with larger samples of spectroscopically surveyed counterparts and more advanced statistical simulations of the match authenticity. Also, the nature of the compact object in two of my counterpart discoveries, the Be HMXB and the symbiotic binary, can be strongly constrained with X-ray spectral fitting. Lastly, I conclude that spectroscopic surveys for new X-ray source counterparts in the GC may be able to increase their efficiency by specifically targeting photometric variables and very close astrometric matches of IR/X-ray sources.

  15. Galactic evolution of sulphur as traced by globular clusters

    NASA Astrophysics Data System (ADS)

    Kacharov, N.; Koch, A.; Caffau, E.; Sbordone, L.

    2015-05-01

    Context. Sulphur is an important volatile α element, but its role in the Galactic chemical evolution is still uncertain, and more observations constraining the sulphur abundance in stellar photospheres are required. Aims: We derive the sulphur abundances in red giant branch (RGB) stars in three Galactic halo globular clusters (GC) that cover a wide metallicity range (-2.3 < [Fe/H] < -1.2): M 4 (NGC 6121), M 22 (NGC 6656), and M 30 (NGC 7099). The halo field stars show a large scatter in the [S/Fe] ratio in this metallicity span, which is inconsistent with canonical chemical evolution models. To date, very few measurements of [S/Fe] exist for stars in GCs, which are good tracers of the chemical enrichment of their environment. However, some light and α elements show star-to-star variations within individual GCs, and it is as yet unclear whether the α element sulphur also varies between GC stars. Methods: We used the infrared spectrograph CRIRES to obtain high-resolution (R ~ 50 000), high signal-to-noise (S/N ~ 200 per px) spectra in the region of the S I multiplet 3 at 1045 nm for 15 GC stars selected from the literature (six stars in M 4,six stars in M 22, and three stars in M 30). Multiplet 3 is better suited for S abundance derivation than the more commonly used lines of multiplet 1 at 920 nm, since its lines are not blended by telluric absorption or other stellar features at low metallicity. Results: We used spectral synthesis to derive the [S/Fe] ratio of the stars assuming local thermodynamic equilibrium (LTE). We find mean [S/Fe]LTE = 0.58 ± 0.01 ± 0.20 dex (statistical and systematic error) for M 4, [S/Fe]LTE = 0.57 ± 0.01 ± 0.19 dex for M 22, and [S/Fe]LTE = 0.55 ± 0.02 ± 0.16 dex for M 30. The negative NLTE corrections are estimated to be in the order of the systematic uncertainties. We do not detect star-to-star variations of the S abundance in any of the observed GCs, with the possible exception of two individual stars, one in M 22 and one in M

  16. Deep Astrometric Standards and Galactic Structure

    NASA Astrophysics Data System (ADS)

    Platais, Imants; Wyse, Rosemary F. G.; Zacharias, Norbert

    2006-01-01

    The advent of next-generation imaging telescopes, such as the Large Synoptic Survey Telescope (LSST) and the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS), has revitalized the need for deep and precise reference frames. The proposed weak-lensing observations with these facilities put the highest demands on image quality over wide angles on the sky. It is particularly difficult to achieve a subarcsecond point-spread function on stacked images, where precise astrometry plays a key role. Current astrometric standards are insufficient to achieve the science goals of these facilities. We thus propose the establishment of a few selected deep (V=25) astrometric standards (DAS). These will enable a reliable geometric calibration of solid-state mosaic detectors in the focal plane of large ground-based telescopes, and will make a substantial contribution to our understanding of stellar populations in the Milky Way. In this paper we examine the need for such standards and discuss the strategy for selecting them and their acquisition and reduction techniques. The feasibility of DAS is demonstrated by a pilot study around the open cluster NGC 188, using the Kitt Peak National Observatory 4 m CCD Mosaic camera, and by Subaru Suprime-Cam observations. The goal of reaching an accuracy of 5-10 mas in positions and obtaining absolute proper motions good to 2 mas yr-1 over a several square-degree area is challenging, but reachable with the NOAO 4 m telescopes and CCD mosaic imagers, or a similar setup. Our proposed DAS aims to establish four fields near the Galactic plane, at widely separated coordinates. In addition to their utilitarian purpose for DAS, the data we will obtain in these fields will enable fundamental Galactic science in their own right. The positions, proper motions, and VI photometry of faint stars will address outstanding questions of Galactic disk formation and evolution, stellar buildup, and mass assembly via merger events.

  17. Galactic Distribution of Planets Spitzer Microlens Parallaxes

    NASA Astrophysics Data System (ADS)

    Gould, Andrew; Carey, Sean; Yee, Jennifer

    2016-08-01

    We will measure the Galactic distribution of planets by obtaining 'microlens parallaxes' of about 700 events, including 18 planetary events, from the comparison of microlens lightcurves observed from Spitzer and Earth, which are separated by 1 AU in projection. As we have demonstrated in two previous programs, the difference in these lightcurves yields both the 'microlens parallax' (ratio of the lens-source relative parallax) to the Einstein radius, and the direction of lens-source relative motion. For planetary events, this measurement directly yields the mass and distance of the planet. For non-planetary events it can be combined with a Galactic model to estimate these quantities with factor 1.4 precision. Hence, the cumulative distributions of planetary events and all events can be compared to determine the relative frequency of planets in the Galactic disk and bulge. The results will be combined with those of current/previous Spitzer campaigns and the current Kepler campaign. This proposal is significantly more sensitive to planets than previous work because it takes advantage of the new KMTNet observing strategy that covers 80 sq.deg at >0.4/hr cadence, 24/7 from 3 southern observatories. This same observing program also provides a unique probe of dark objects. It will yield the first mass-measurement based determination of the isolated-brown-dwarf mass function. Thirteen percent of the observations will specifically target binaries, which will probe systems with dark components (brown dwarfs, neutron stars, black holes) that are difficult or impossible to investigate by other methods. The observations and methods from this work are a test bed for WFIRST microlensing.

  18. Determination of the real number of galaxies in clusters of galaxies taking into consideration starlike red compact galaxies

    NASA Astrophysics Data System (ADS)

    Richter, N.

    Optical compact galaxies and red starlike objects are selected in two neighboring fields of 0.8 sq deg near the galactic north pole on an objective prism plate. With an identification magnitude of 18.9 m (B), 49 compact galaxies and 96 starlike objects are found in field I. In field II, nine compact galaxies and 41 red starlike objects are found. 55 of the 96 starlike objects in field I are determined to be optical compact galaxies, indicating an enlargement of the number of galaxies by 50 percent. The 96 red objects are also inspected on an FOA plate, 24 of which are found to be compact starlike galaxies.

  19. Modeling Galactic Halos with Predominantly Quintessential Matter

    NASA Astrophysics Data System (ADS)

    Rahaman, F.; Kuhfittig, Peter K. F.; Chakraborty, K.; Kalam, M.; Hossain, D.

    2011-09-01

    This paper discusses a new model for galactic dark matter by combining an anisotropic pressure field corresponding to normal matter and a quintessence dark energy field having a characteristic parameter ω q such that -1<ωq< -1/3. Stable stellar orbits together with an attractive gravity exist only if ω q is extremely close to -1/3, a result consistent with the special case studied by Guzman et al. (Rev. Mex. Fis. 49:303, 2003). Less exceptional forms of quintessence dark energy do not yield the desired stable orbits and are therefore unsuitable for modeling dark matter.

  20. Fermi-LAT Observations of Galactic Transients

    NASA Technical Reports Server (NTRS)

    Hays, Elizabeth

    2011-01-01

    This slide presentation reviews the observations of Galactic transients by the Large Area Telescope (LAT) on the Fermi Gamma Ray Space Telescope. The LAT is producing spectacular results for the GeV transient sky, some of which are shown and reviewed. Some of the results in the GeV range that are discussed in this presentation are: (1) New blazars and unidentified transients (2) the jet of the Cygnus X-3 microquasar (3) gamma rays from V407 Cygni nova (4) Fast high-energy gamma-ray flares from the Crab Nebula

  1. Updated galactic radio constraints on Dark Matter

    NASA Astrophysics Data System (ADS)

    Cirelli, Marco; Taoso, Marco

    2016-07-01

    We perform a detailed analysis of the synchrotron signals produced by dark matter annihilations and decays. We consider different set-ups for the propagation of electrons and positrons, the galactic magnetic field and dark matter properties. We then confront these signals with radio and microwave maps, including Planck measurements, from a frequency of 22 MHz up to 70 GHz. We derive two sets of constraints: conservative and progressive, the latter based on a modeling of the astrophysical emission. Radio and microwave constraints are complementary to those obtained with other indirect detection methods, especially for dark matter annihilating into leptonic channels.

  2. Time variation of galactic cosmic rays

    NASA Technical Reports Server (NTRS)

    Evenson, Paul

    1988-01-01

    Time variations in the flux of galactic cosmic rays are the result of changing conditions in the solar wind. Maximum cosmic ray fluxes, which occur when solar activity is at a minimum, are well defined. Reductions from this maximum level are typically systematic and predictable but on occasion are rapid and unexpected. Models relating the flux level at lower energy to that at neutron monitor energy are typically accurate to 20 percent of the total excursion at that energy. Other models, relating flux to observables such as sunspot number, flare frequency, and current sheet tilt are phenomenological but nevertheless can be quite accurate.

  3. The Herschel view of the Galactic center

    NASA Astrophysics Data System (ADS)

    Bally, John; Hi-GAL Team

    2014-05-01

    The 3.5 meter diameter Herschel Space Observatory conducted a ˜720 square-degree survey of the Galactic plane, the Herschel Galactic plane survey (Hi-GAL). These data provide the most sensitive and highest resolution observations of the far-IR to sub-mm continuum from the central molecular zone (CMZ) at λ = 70, 160, 250, 350, and 500 μm obtained to date. Hi-GAL can be used to map the distributions of temperature and column density of dust in CMZ clouds, warm dust in Hii regions, and identify highly embedded massive protostars and clusters and the dusty shells ejected by supergiant stars. These data enable classification of sources and re-evaluation of the current and recent star-formation rate in the CMZ. The outer CMZ beyond |l| = 0.9 degrees (Rgal > 130 pc) contains most of the dense (n > 104 cm-3 gas in the Galaxy but supports very little star formation. The Hi-GAL and Spitzer data show that almost all star formation occurs in clouds moving on x 2 orbits at Rgal < 100 pc. While the 106 M⊙ Sgr B2 complex, the 50 km s-1 cloud near Sgr A, and the Sgr C region are forming clusters of massive stars, other clouds are relatively inactive star formers, despite their high densities, large masses, and compact sizes. The asymmetric distribution of dense gas about Sgr A* on degree scales (most dense CMZ gas and dust is at positive Galactic longitudes and positive VLSR ) and compact 24 μm sources (most are at negative longitudes) may indicate that eposidic mini-starbursts occasionally `blow-out' a portion of the gas on these x 2 orbits. The resulting massive-star feedback may fuel the compact 30 pc scale Galactic center bubble associated with the Arches and Quintuplet clusters, the several hundred pc scale Sofue-Handa lobe, and the kpc-scale Fermi/LAT bubble, making it the largest `superbubble' in the Galaxy. A consequence of this model is that in our Galaxy, instead of the supermassive black hole (SMBH) limiting star formation, star formation may limit the growth of

  4. Kinematic Distances of Galactic Planetary Nebulae

    NASA Astrophysics Data System (ADS)

    Yang, A. Y.; Tian, W. W.; Zhu, H.; Leahy, D. A.; Wu, D.

    2016-03-01

    We construct H i absorption spectra for 18 planetary nebulae (PNs) and their background sources using data from the International Galactic Plane Survey. We estimate the kinematic distances of these PNs, among which 15 objects’ kinematic distances are obtained for the first time. The distance uncertainties of 13 PNs range from 10% to 50%, which is a significant improvement with uncertainties of a factor of two or three smaller than most previous distance measurements. We confirm that PN G030.2-00.1 is not a PN because of its large distance found here.

  5. EGRET Sources at Intermediate Galactic Latitudes

    NASA Technical Reports Server (NTRS)

    Halpern, Jules P.

    1998-01-01

    During the period 15 March 1992 through 31 October 1997, 12 papers using ROSAT data, supported in part by this grant, were published in referred journals, and one paper was published in a conference proceedings. Their bibliographical references are listed in the Appendix, and the abstracts of these papers are given in the next 13 sections of this report. Finally, a summary of the work completed to date on the newest project, for which ROSAT data are still being received, is given in the section entitled "EGRET Sources at Intermediate Galactic Latitude".

  6. Spatially integrated spectroscopy of Galactic HII regions.

    NASA Astrophysics Data System (ADS)

    Robledo-Rella, V.

    2000-11-01

    We present optical-NIR spatially integrated spectroscopy of 7 Galactic HII regions: Carina, M8, M20, RCW6, RCW60, RCW107 and RCW110/111. The effect of the embedded ionizing stars' spectra on the nebular spectra is studied. The distribution of Balmer Equivalent Widths in the combined spectra (nebular plus stellar) is slightly stepper than in the pure nebular spectra. The comparison of this distribution in Extragalactic HII regions and HII/Starbust galaxies may yield a more accurate determination of the underlaying stellar absorption (or emission!) affecting the observed Balmer lines used to derive extinction and other physical parameters of the emitting regions and associated stellar clusters.

  7. Quantifying radio-mode feedback from Active Galactic Nuclei

    NASA Astrophysics Data System (ADS)

    Shabala, Stanislav

    2015-08-01

    Galaxy formation models routinely invoke feedback from radio-loud Active Galactic Nuclei to explain the observed masses and red colours of the most massive galaxies since z~1. Whether or not the observed AGN population can provide the required feedback, however, is an open question.We present a new dynamical model that relates AGN physical parameters to the observed properties of radio AGN. This model combines a traditional approach to modeling radio AGN with a semi-analytic description of AGN environments. The model reproduces a number of key features of the observed radio AGN populations, and we determine the energetics (specifically, jet kinetic powers and AGN lifetimes) of the observed local (z<0.1) radio AGN population, as a function of host galaxy properties.We find a broad distribution of jet powers that is largely independent of host galaxy mass, consistent with the idea that these radio AGN are fed by gas cooling from hot haloes in near heating-cooling equilibrium. On the other hand, the duration of the AGN phase appears strongly mass-dependent: massive galaxies host AGN that are longer-lived, and can therefore impart feedback for longer and on larger spatial scales. Finally, we compare the cumulative AGN energy output from ubiquitous weak AGN with their rare powerful counterparts, and find that radio AGN of all luminosities deliver a comparable amount of energy to their surroundings.I will outline how this approach can provide useful insights into AGN triggering and feedback mechanisms, as well as be used to correct for selection effects in large radio surveys. I will also outline the challenges (and solutions) to performing an AGN energetics analysis at high redshift.

  8. Near-infrared spectroscopy of candidate red supergiant stars in clusters

    NASA Astrophysics Data System (ADS)

    Messineo, Maria; Zhu, Qingfeng; Ivanov, Valentin D.; Figer, Donald F.; Davies, Ben; Menten, Karl M.; Kudritzki, Rolf P.; Chen, C.-H. Rosie

    2014-11-01

    Context. Clear identifications of Galactic young stellar clusters farther than a few kpc from the Sun are rare, despite the large number of candidate clusters. Aims: We aim to improve the selection of candidate clusters rich in massive stars with a multiwavelength analysis of photometric Galactic data that range from optical to mid-infrared wavelengths. Methods: We present a photometric and spectroscopic analysis of five candidate stellar clusters, which were selected as overdensities with bright stars (Ks< 7 mag) in GLIMPSE and 2MASS images. Results: A total of 48 infrared spectra were obtained. The combination of photometry and spectroscopy yielded six new red supergiant stars with masses from 10 M⊙ to 15 M⊙. Two red supergiants are located at Galactic coordinates (l,b) = (16.°7, -0.°63) and at a distance of about ~3.9 kpc; four other red supergiants are members of a cluster at Galactic coordinates (l,b) = (49.°3, + 0.°72) and at a distance of ~7.0 kpc. Conclusions: Spectroscopic analysis of the brightest stars of detected overdensities and studies of interstellar extinction along their line of sights are fundamental to distinguish regions of low extinction from actual stellar clusters. The census of young star clusters containing red supergiants is incomplete; in the existing all-sky near-infrared surveys, they can be identified as overdensities of bright stars with infrared color-magnitude diagrams characterized by gaps. Based on observations collected at the European Southern Observatory (ESO Programme 60.A-9700(E), and 089.D-0876), and on observations collected at the UKIRT telescope (programme ID H243NS).MM is currently employed by the MPIfR. Part of this work was performed at RIT (2009), at ESA (2010), and at the MPIfR.Tables 3, 4, and 6 are available in electronic form at http://www.aanda.org

  9. Zinc abundances in Galactic bulge field red giants: Implications for damped Lyman-α systems

    NASA Astrophysics Data System (ADS)

    Barbuy, B.; Friaça, A. C. S.; da Silveira, C. R.; Hill, V.; Zoccali, M.; Minniti, D.; Renzini, A.; Ortolani, S.; Gómez, A.

    2015-08-01

    Context. Zinc in stars is an important reference element because it is a proxy to Fe in studies of damped Lyman-α systems (DLAs), permitting a comparison of chemical evolution histories of bulge stellar populations and DLAs. In terms of nucleosynthesis, it behaves as an alpha element because it is enhanced in metal-poor stars. Abundance studies in different stellar populations can give hints to the Zn production in different sites. Aims: The aim of this work is to derive the iron-peak element Zn abundances in 56 bulge giants from high resolution spectra. These results are compared with data from other bulge samples, as well as from disk and halo stars, and damped Lyman-α systems, in order to better understand the chemical evolution in these environments. Methods: High-resolution spectra were obtained using FLAMES+UVES on the Very Large Telescope. We computed the Zn abundances using the Zn i lines at 4810.53 and 6362.34 Å. We considered the strong depression in the continuum of the Zn i 6362.34 Å line, which is caused by the wings of the Ca i 6361.79 Å line suffering from autoionization. CN lines blending the Zn i 6362.34 Å line are also included in the calculations. Results: We find [Zn/Fe] = +0.24 ± 0.02 in the range -1.3 < [Fe/H] < -0.5 and [Zn/Fe] = + 0.06 ± 0.02 in the range -0.5 < [Fe/H] < -0.1, whereas for [Fe/H] ≥ -0.1, it shows a spread of -0.60 < [Zn/Fe] < + 0.15, with most of these stars having low [Zn/Fe] < 0.0. These low zinc abundances at the high metallicity end of the bulge define a decreasing trend in [Zn/Fe] with increasing metallicities. A comparison with Zn abundances in DLA systems is presented, where a dust-depletion correction was applied for both Zn and Fe. When we take these corrections into account, the [Zn/Fe] vs. [Fe/H] of the DLAs fall in the same region as the thick disk and bulge stars. Finally, we present a chemical evolution model of Zn enrichment in massive spheroids, representing a typical classical bulge evolution. Observations collected both at the European Southern Observatory, Paranal, Chile (ESO programmes 71.B-0617A, 73.B0074A, and GTO 71.B-0196).Table 6 is available in electronic form at http://www.aanda.org

  10. VizieR Online Data Catalog: Candidate red supergiants in Galactic clusters (Messineo+, 2014)

    NASA Astrophysics Data System (ADS)

    Messineo, M.; Zhu, Q. F.; Ivanov, V. D.; Figer, D. F.; Davies, B.; Menten, K. M.; Kudritzki, R. P.; Chen, C.-H. R.

    2015-01-01

    A set of spectroscopic data was taken with the UKIRT 1-5-micron Imager Spectrometer (UIST) on Mauna Kea under program ID H243NS (PI: Kudritzki) on 2008 July 24. For four of the targeted candidate clusters, additional low-resolution and medium-resolution spectra were obtained with the SofI spectrograph mounted on the NTT telescope. Data were taken under program 60.A-9700(E) at Paranal-La Silla Observatory on 2010 August 3, and under program 089.D-0876 on 2012 June 1. (3 data files).

  11. The tricky galactic cluster NGC 2420

    NASA Astrophysics Data System (ADS)

    Prada Moroni, P. G.; Castellani, V.; degl'Innocenti, S.; Marconi, M.

    We discuss the CM diagram of the galactic cluster NGC 2420 to the light of current theoretical predictions. By relying on the most recent updating of the physical input, one finds too luminous theoretical He burning stars together with the evidence for a misfitting of the lower portion of the MS. Moreover one finds two well known overshooting signatures, as given by 1) the large extension of the "hook" preceding the overall contraction gap, and 2) the scarcity of stars just at the end of the gap. We show that the overluminosity of He burning stars appears as a constant prediction of models based on updated physics, whereas alternative assumptions about the Equation of State can account for the MS fitting. Moreover, due to the scarce statistical significance of the observational sample, one finds that overshooting signatures can be present also in canonical (without overshooting) predictions. We conclude that, unfortunately, NGC 2420 does not keep the promise to be of help in constraining the actual dimensions of convective cores in H burning MS stars, suggesting in the meantime that using clumping He burning stars as theoretical standard candle is at least a risky procedure. In this context the need for firmer constraints about the reddening of galactic clusters is shortly discussed.

  12. Radio polarimetry of Galactic Centre pulsars

    NASA Astrophysics Data System (ADS)

    Schnitzeler, D. H. F. M.; Eatough, R. P.; Ferrière, K.; Kramer, M.; Lee, K. J.; Noutsos, A.; Shannon, R. M.

    2016-07-01

    To study the strength and structure of the magnetic field in the Galactic Centre (GC), we measured Faraday rotation of the radio emission of pulsars which are seen towards the GC. Three of these pulsars have the largest rotation measures (RMs) observed in any Galactic object with the exception of Sgr A⋆. Their large dispersion measures, RMs and the large RM variation between these pulsars and other known objects in the GC implies that the pulsars lie in the GC and are not merely seen in projection towards the GC. The large RMs of these pulsars indicate large line-of-sight magnetic field components between ˜ 16 and 33 μG; combined with recent model predictions for the strength of the magnetic field in the GC this implies that the large-scale magnetic field has a very small inclination angle with respect to the plane of the sky (˜12°). Foreground objects like the Radio Arc or possibly an ablated, ionized halo around the molecular cloud G0.11-0.11 could contribute to the large RMs of two of the pulsars. If these pulsars lie behind the Radio Arc or G0.11-0.11 then this proves that low-scattering corridors with lengths ≳100 pc must exist in the GC. This also suggests that future, sensitive observations will be able to detect additional pulsars in the GC. Finally, we show that the GC component in our most accurate electron density model oversimplifies structure in the GC.

  13. Rice University observations of the galactic center

    NASA Technical Reports Server (NTRS)

    Meegan, C. A.

    1978-01-01

    The most sensitive of the four balloon fight observations of the galactic center made by Rice University was conducted in 1974 from Rio Cuarto, Argentina at a float altitude of 4 mbar. The count rate spectrum of the observed background and the energy spectrum of the galactic center region are discussed. The detector used consists of a 6 inch Nal(T 1ambda) central detector collimated to approximately 15 deg FWHM by a Nal(T lamdba) anticoincidence shield. The shield in at least two interaction mean free paths thick at all gamma ray energies. The instrumental resolution is approximately 11% FWHM at 662 keV. Pulses from the central detector are analyzed by two 256 channel PHA's covering the energy range approximately 20 keV to approximately 12 MeV. The detector is equatorially mounted and pointed by command from the ground. Observations are made by measuring source and background alternately for 10 minute periods. Background is measured by rotating the detector 180 deg about the azimuthal axis.

  14. Galactic sources of high energy neutrinos

    NASA Astrophysics Data System (ADS)

    Aharonian, Felix

    2011-12-01

    The undisputed galactic origin of cosmic rays at energies below the so-called knee implies an existence of a nonthemal population of galactic objects which effectively accelerate protons and nuclei to TeV-PeV energies. The distinct signatures of these cosmic PeVatrons are high energy neutrinos and γ-rays produced through hadronic interactions. While γ-rays can be produced also by directly accelerated electrons, high energy neutrinos provide the most straightforward and unambiguous information about the nucleonic component of accelerated particles. The planned km3-volume class high energy neutrino detectors are expected to be sensitive enough to provide the first astrophysically meaningful probes of potential VHE neutrino sources. This optimistic prediction is based on the recent discovery of high energy γ-ray sources with hard energy spectra extending to 10 TeV and beyond. Amongst the best-bet candidates are two young shell-type supernova remnants - RXJ 1713.7-4946 and RXJ 0852.0-4622, and perhaps also two prominent plerions - the Crab Nebula and Vela X. Because of strong absorption of TeV γ-rays, one may expect detectable neutrino fluxes also from (somewhat fainter) compact TeV γ-ray emitters like the binary systems LS 5039 and LS I+61 303, and, hopefully, also from hypothetical "hidden" or "orphan" neutrino sources.

  15. VERITAS Observations of The Galactic Center Ridge

    NASA Astrophysics Data System (ADS)

    Smith, Andrew W

    2014-08-01

    The Galactic Center Ridge is perhaps the most local, busy environment for high-energy particle acceleration, harboring as it does many relativistic particle accelerators such as pulsar wind nebulae, supernova remnants, and the central supermassive black hole SgrA*. Observations with very high energy (VHE, >100 GeV) gamma-ray telescopes of the region have revealed multiple point sources associated with well-known objects, as well as regions of extended emission not directly associated with sources at other wavelengths. More importantly, the detection of a large, diffuse component of >300 GeV gamma-ray emission by the HESS collaboration is strongly believed to be the result of accelerated cosmic rays interacting with molecular-cloud regions, thus providing insight into high-energy cosmic ray acceleration. Here we present the VERITAS observations of the Galactic Center Ridge taken from 2008-2014 in the >2 TeV regime. We will focus on the VERITAS results on the known HESS sources in the region, as well as the diffuse component of TeV emission along the plane. Due to the much higher energy threshold of the VERITAS observations, our data provide a new window into some of the highest energy particle acceleration occurring in the center of our galaxy.

  16. VERITAS Observations of The Galactic Center Ridge

    NASA Astrophysics Data System (ADS)

    Smith, Andrew; Veritas

    2015-01-01

    The Galactic Center Ridge is perhaps the most local, busy environment for high energy particle acceleration; home to many relativistic particle accelerators such as pulsar wind nebulae, supernova remnants, and the central supermassive black hole SgrA*. Observations with VHE (>100 GeV) gamma-ray telescopes of the region have revealed multiple point sources associated with well known objects, as well as regions of extended emission not directly associated with targets at other wavelengths. More importantly, the detection of a large, diffuse component of >300 GeV gamma-ray emission by the HESS collaboration is strongly believed to be the result of accelerated cosmic rays interacting with molecular cloud regions, thus providing a window into high energy cosmic ray acceleration. Here we present the VERITAS observations of the Galactic Center Ridge taken from 2008-2014 in the >2 TeV regime. We will focus on the VERITAS results on the known HESS sources in the region, as well as the diffuse component of TeV emission along the plane. Due to the much higher energy threshold of the VERITAS observations, our data provide a new window into some of the highest energy particle acceleration occurring in the center of our galaxy.

  17. Understanding the kinematics of Galactic centre gas

    NASA Astrophysics Data System (ADS)

    Binney, James; Gerhard, Ortwin E.; Stark, Antony A.; Bally, John; Uchida, Keven I.

    1991-09-01

    A coherent picture is constructed of the Galaxy's H I, CO and CS emissions in the region l below 10 deg, b below 0.5 deg. The flow of gas at the Galactic center is dominated by a bar that has corotation at r = 2.4 + or - 0.5 kpc, which is viewed at an angle of 16 + or - 2 deg from its major axis. The first CO emission arises where gas is obliged to switch from x(1) orbits to x(2) orbits, in the notation of Contopoulos. This gives rise to a shock and a clear signature in the (l, v) diagram. The great Galactic center molecular clouds such as Sgr B, are on x(2) orbits. From the structure of the H I terminal velocity envelope, it is deduced that the central mass density scales as rho varies with r to the -1.75 power out to at least about 1.2 kpc along the bar's major axis. Consequently, the circular velocity curve is rising significantly through the radius range where naive analysis of the tangent velocity leads to a falling rotation curve. The great ring of molecular material at r of about 3.5 kpc is probably associated with the bar's outer Lindblad resonance, and the region of low gas densities inward from there with corotation.

  18. The chemical composition of Galactic beat Cepheids

    NASA Astrophysics Data System (ADS)

    Kovtyukh, V.; Lemasle, B.; Chekhonadskikh, F.; Bono, G.; Matsunaga, N.; Yushchenko, A.; Anderson, R. I.; Belik, S.; da Silva, R.; Inno, L.

    2016-08-01

    We determine the metallicity and detailed chemical abundances (α, iron-peak and neutron-capture elements) for the almost complete (18/24) sample of Galactic double mode Cepheids (also called beat Cepheids). Double mode Cepheids are Cepheids that pulsate in two modes simultaneously. We calibrate a new relation between their metallicity and their period ratio P1/P0. This linear relation allows to determine the metallicity of bimodal Cepheids with an accuracy of 0.03 dex in the range of [Fe/H] from +0.2 to -0.5 dex. By extrapolating the relation to Magellanic Clouds beat Cepheids, we provide their metallicity distribution function. Moreover, by using this relation, we also provide the first metallicity estimate for two double-mode F/1O Cepheids located in and beyond the Galactic bulge. Finally, we report the discovery of a super-Lithium rich double mode Cepheid V371 Per which has a Lithium abundance of logA(Li) = 3.54 ± 0.09 dex. Along with V1033 Cyg (which is an ordinary classical Cepheid), it is the second known Cepheid of such type in the Galaxy.

  19. Light Echoes of Galactic Explosions and Eruptions

    NASA Astrophysics Data System (ADS)

    Rest, Armin; Bianco, Federica; Chornock, Ryan; Foley, Ryan; Matheson, Thomas; Narayan, Gautham; Olsen, Knut; Prieto, Jose Luis; Smith, Chris; Smith, Nathan; Suntzeff, Nick; Welch, Doug; Zenteno, Alfredo

    2014-02-01

    We propose to continue our search for the first light echoes (LEs) associated with historical Galactic supernovae and LBV outbursts: SN 1006, Kepler's SN, RCW 86, Crab Nebula, and P Cygni. In previously granted NOAO time, we have discovered LEs of three ancient SNe in the LMC as well as from the historic SN events of Cas A and Tycho [2, 3], which allowed their spectroscopic classification [6, 7, 10] and 3D spectroscopy [8, 9]. Most recently, we discovered light echoes of the mid-19th-century Great Eruption of η Carinae using CTIO 4m Mosaic images [11]. Subsequent spectroscopic follow-up of Eta Carinae revealed that its outburst spectral type was most similar to those of G-type supergiants, rather than reported LBV outburst spectral types of F-type (or earlier) [11]. We propose to continue our search for light echoes of the remaining historical events. With DECam, we have a 10-15 fold improvement in efficiency over the retired CTIO-Mosaic camera, which allows us to cover the bigger search areas of most of the remaining targets. With the KPNO 4-m, we will observe fields too far north for CTIO/DECam. The study of scattered-light echoes from these Galactic supernovae and eruptions will give us the opportunity to directly compare the original outburst and its current remnant, and in favorable cases (like Eta Carinae), it provides a three-dimensional view of the event and/or a spectral time series.

  20. Light Echoes of Galactic Explosions and Eruptions

    NASA Astrophysics Data System (ADS)

    Rest, Armin; Bianco, Federica; Chornock, Ryan; Foley, Ryan; Matheson, Thomas; Olsen, Knut; Prieto, Jose Luis; Sinnott, Brendan; Smith, Chris; Smith, Nathan; Welch, Doug

    2013-02-01

    We propose to continue our search for the first light echoes (LEs) associated with historical Galactic supernovae and LBV outbursts: SN 1006, Kepler's SN, RCW 86, Crab Nebula, and P Cygni. In previously granted NOAO time, we have discovered light echoes of three ancient SNe in the LMC as well as from the historic SN events of Cas A and Tycho [2, 3], which allowed their spectroscopic classification [6, 7, 10] and 3D spectroscopy [8, 9]. Most recently, we discovered light echoes of the mid-19th-century Great Eruption of eta Carinae using CTIO 4m Mosaic images [11]. Subsequent spectroscopic follow-up of Eta Carinae revealed that its outburst spectral type was most similar to those of G-type supergiants, rather than reported LBV outburst spectral types of F-type (or earlier) [11]. We propose to continue our search for light echoes of the remaining historical events. With DECam, we have a 10-15 fold improvement in efficiency over the retired Mosaic camera, which allows us to cover the bigger search areas of most of the remaining targets. The study of scattered-light echoes from these Galactic supernovae and eruptions will give us the opportunity to directly compare the original outburst and its current remnant, and in favorable cases (like Eta Carinae), it provides a three-dimensional view of the event and/or a spectral time series.