DOCSLIB.ORG

Lithium and Zirconium Abundances in Massive Galactic O-Rich AGB Stars,

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Lithium and Zirconium Abundances in Massive Galactic O-Rich AGB Stars�, A&A 462, 711–730 (2007) Astronomy DOI: 10.1051/0004-6361:20065785 & c ESO 2007 Astrophysics Lithium and zirconium abundances in massive Galactic O-rich AGB stars, D. A. García-Hernández1 , P. García-Lario1,2,B.Plez3, A. Manchado4,5, F. D’Antona6,J.Lub7, and H. Habing7 1 ISO Data Centre, Research and Scientific Support Department of ESA. European Space Astronomy Centre (ESAC), Villafranca del Castillo, PO Box 50727, 28080 Madrid, Spain e-mail: [email protected] 2 Herschel Science Centre, Research and Scientific Support Department of ESA. European Space Astronomy Centre (ESAC), Villafranca del Castillo, PO Box 50727, 28080 Madrid, Spain e-mail: [email protected] 3 GRAAL, CNRS UMR 5024, Université de Montpellier 2, 34095 Montpellier Cedex 5, France e-mail: [email protected] 4 Instituto de Astrofísica de Canarias, La Laguna 38200, Tenerife, Spain e-mail: [email protected] 5 Consejo Superior de Investigaciones Científicas (CSIC), Spain 6 Osservatorio Astronomico di Roma, via Frascati 33, 00040 MontePorzio Catone, Italy e-mail: [email protected] 7 Sterrewacht Leiden, Niels Bohrweg 2, 2333 RA Leiden, The Netherlands Received 8 June 2006 / Accepted 25 August 2006 ABSTRACT 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. Key words. stars: AGB and post-AGB – stars: abundances – stars: evolution – nuclear reactions, nucleosynthesis, abundances – stars: atmospheres – stars: late-type 1. Introduction C-rich AGB stars (C/O > 1). This scenario would explain the observed spectral sequence M–MS–S–SC–C in AGB stars (e.g. The asymptotic giant branch (AGB) is formed by stars with ini- Mowlavi 1999). tial masses in the range between 0.8 and 8 M in a late stage of their evolution. The internal structure of an AGB star con- Another important characteristic of AGB stars is the pres- sists of an electron-degenerate C–O core surrounded by a shell ence of neutron-rich elements (s-elements such as Sr, Y, Zr, of He. During most of the time H burning is the main source Ba, La, Nd, Tc, etc.) in their atmospheres. These species are of energy for the AGB star but, occasionally, the inner He shell formed by slow-neutron captures in the intershell region. After a dredge-up episode, according to theoretical models, protons can ignites in a “thermal pulse”; and eventually, the byproducts of 12 4 He burning may reach the outer layers of the atmosphere in a be partially mixed in the C- and He-rich region between the “dredge-up” of processed material (the so-called third dredge- hydrogen- and helium-burning shells (e.g. Straniero et al. 1995, 1997; Mowlavi 2002; Lattanzio 2003) and can react with 12Cto up). Repeated thermal pulses add carbon to the stellar surface. 13 13 16 As a consequence, originally O-rich AGB stars can turn into form C during the interpulse phase. The C(α,n) O reaction releases neutrons, which are captured by iron nuclei and other heavy elements, forming s-elements that can later be dredged up Based on observations at the 4.2 m William Herschel Telescope to the stellar surface in the next thermal pulse (Straniero et al. operated on the island of La Palma by the Isaac Newton Group in the 1995, 1997; Busso et al. 2001). Spanish Observatorio del Roque de Los Muchachos of the Instituto de 22 Astrofisica de Canarias. Also based on observations with the ESO 3.6 m Another neutron source, Ne, needs to be considered. In telescope at La Silla Observatory (Chile). this case the activation takes place during the convective ther- Tables 1–9 are only available in electronic form at mal pulses (e.g. Straniero et al. 1995, 2000; Vaglio et al. http://www.aanda.org 1999; Gallino et al. 2000). 22Ne can be formed from 14N, Article published by EDP Sciences and available at http://www.aanda.org or http://dx.doi.org/10.1051/0004-6361:20065785 712 D. A. García-Hernández et al.: Li and Zr in massive Galactic O-rich AGBs and 14N is formed by the CNO cycle in the hydrogen shell. are the so-called OH/IR stars, luminous O-rich AGB stars that The 22Ne(α,n)25Mg neutron source requires higher tempera- are extremely bright in the infrared, showing a characteristic tures and typically occurs at higher neutron densities than the double-peaked OH maser emission at 1612 MHz. These stars 13C(α,n)16O reaction. Thus, a different s-element pattern is ex- are also known to be very long period variables (LPVs), some- pected depending on the dominant neutron source. According times with periods of more than 500 days and large amplitudes of to the most recent models, the 13C(α,n)16O reaction is the pre- up to 2 bolometric magnitudes. However, they experience very −5 −1 ferred neutron source for masses around 1−3 M, while for more strong mass loss rates (up to several times 10 M yr )atthe massive stars (i.e. M ∼> 3−4 M) neutrons are thought to be end of the AGB, and most of them appear heavily obscured by mainly released through the 22Ne(α,n)25Mg reaction (see, for ex- thick circumstellar envelopes, making optical observations very ample, Busso et al. 1999 and Lattanzio & Lugaro 2005, for a re- difficult (e.g. Kastner et al. 1993; Jiménez-Esteban et al. 2005a, cent review). In the literature, there is strong evidence that most 2006a). Thus, no information exists yet on their lithium abun- Galactic AGB stars enriched in s-process elements have masses dances and/or possible s-process element enrichment. 13 16 around 1−3 M,wherethe C(α,n) O reaction is the neutron In this paper we present results from a wide observational donor (e.g. Lambert et al. 1995; Abia et al. 2001). Unfortunately, programme based on high-resolution optical spectroscopy of a a confrontation of the predictions made by these models with ob- carefully selected sample of Galactic AGB stars thought to be servations of more massive AGB stars in our Galaxy is not yet massive from their observational properties. The criteria fol- available. lowed to select the sources in the sample are explained in Sect. 2. In the case of the more massive O-rich AGB stars (M > The high-resolution spectroscopic observations made in the opti- 3−4 M), the convective envelope can penetrate the H-burning cal and the data reduction process are described in Sect. 3, while shell thereby activating so-called “hot bottom burning” (here- the main results are presented in Sect. 4. In this section we also after, HBB), which takes place when the temperature at the show how spectral synthesis techniques were applied to derive base of the convective envelope is hot enough (T ≥ 2 × the atmospheric parameters, as well as the lithium and zirconium 107 K) and 12C can be converted into 13Cand14N through the abundances, of the stars in our sample. A discussion of these re- CN cycle (Sackmann & Boothroyd 1992; Wood et al. 1983). sults in the context of HBB models, nucleosynthesis models, and The HBB models (Sackmann & Boothroyd 1992; D’Antona & stellar evolution can be found in Sect. 5. Finally, the conclusions Mazzitelli 1996; Mazzitelli et al. 1999) also predict the produc- derived from this work are given in Sect. 6. tion of the short-lived 7Li by the chain 3He(α,γ)7Be (e−,v)7Li, through the so-called “7Be transport mechanism” (Cameron & Fowler 1971). One of the predictions of these models is that 2. Selection of the sample lithium should be detectable, at least for some time, on the stellar − surface. A large sample of long period (300 1000 days), large ampli- − Activation of HBB in massive O-rich AGB stars is supported tude variability (up to 8 10magintheV band), late-type (>M5) by studies of AGB stars in the Magellanic Clouds (hereafter, O-rich AGB stars displaying OH maser emission with a wide range of expansion velocities (from just a few km s−1 to more MCs) (Plez et al. 1993; Smith & Lambert 1989, 1990a; Smith −1 et al. 1995), which show a lack of high-luminosity C stars be- than 20 km s ) was carefully selected from the literature. These sources are all very bright in the infrared and, as such, included yond Mbol ∼−6.
Load more

Recommended publications
  • The Evolution of Helium White Dwarfs: Applications to Millisecond
    Pulsar Astronomy — 2000 and Beyond ASP Conference Series, Vol. 3 × 108, 1999 M. Kramer, N. Wex, and R. Wielebinski, eds. The evolution of helium white dwarfs: Applications for millisecond pulsars T. Driebe and T. Bl¨ocker Max-Planck-Institut f¨ur Radioastronomie, Bonn, Germany D. Sch¨onberner Astrophysikalisches Institut Potsdam, Potsdam, Germany 1. White Dwarf Evolution Low-mass white dwarfs with helium cores (He-WDs) are known to result from mass loss and/or exchange events in binary systems where the donor is a low mass star evolving along the red giant branch (RGB). Therefore, He-WDs are common components in binary systems with either two white dwarfs or with a white dwarf and a millisecond pulsar (MSP). If the cooling behaviour of He- WDs is known from theoretical studies (see Driebe et al. 1998, and references therein) the ages of MSP systems can be calculated independently of the pulsar properties provided the He-WD mass is known from spectroscopy. Driebe et al. (1998, 1999) investigated the evolution of He-WDs in the mass range 0.18 < MWD/M⊙ < 0.45 using the code of Bl¨ocker (1995). The evolution of a 1 M⊙-model was calculated up to the tip of the RGB. High mass loss termi- nated the RGB evolution at appropriate positions depending on the desired final white dwarf mass. When the model started to leave the RGB, mass loss was virtually switched off and the models evolved towards the white dwarf cooling branch. The applied procedure mimicks the mass transfer in binary systems. Contrary to the more massive C/O-WDs (MWD ∼> 0.5 M⊙, carbon/oxygen core), whose progenitors have also evolved through the asymptotic giant branch phase, He-WDs can continue to burn hydrogen via the pp cycle along the cooling branch arXiv:astro-ph/9910230v1 13 Oct 1999 down to very low effective temperatures, resulting in cooling ages of the order of Gyr, i.
    [Show full text]
  • The Deaths of Stars
    The Deaths of Stars 1 Guiding Questions 1. What kinds of nuclear reactions occur within a star like the Sun as it ages? 2. Where did the carbon atoms in our bodies come from? 3. What is a planetary nebula, and what does it have to do with planets? 4. What is a white dwarf star? 5. Why do high-mass stars go through more evolutionary stages than low-mass stars? 6. What happens within a high-mass star to turn it into a supernova? 7. Why was SN 1987A an unusual supernova? 8. What was learned by detecting neutrinos from SN 1987A? 9. How can a white dwarf star give rise to a type of supernova? 10.What remains after a supernova explosion? 2 Pathways of Stellar Evolution GOOD TO KNOW 3 Low-mass stars go through two distinct red-giant stages • A low-mass star becomes – a red giant when shell hydrogen fusion begins – a horizontal-branch star when core helium fusion begins – an asymptotic giant branch (AGB) star when the helium in the core is exhausted and shell helium fusion begins 4 5 6 7 Bringing the products of nuclear fusion to a giant star’s surface • As a low-mass star ages, convection occurs over a larger portion of its volume • This takes heavy elements formed in the star’s interior and distributes them throughout the star 8 9 Low-mass stars die by gently ejecting their outer layers, creating planetary nebulae • Helium shell flashes in an old, low-mass star produce thermal pulses during which more than half the star’s mass may be ejected into space • This exposes the hot carbon-oxygen core of the star • Ultraviolet radiation from the exposed
    [Show full text]
  • EVOLVED STARS a Vision of the Future Astron
    PUBLISHED: 04 JANUARY 2017 | VOLUME: 1 | ARTICLE NUMBER: 0021 research highlights EVOLVED STARS A vision of the future Astron. Astrophys. 596, A92 (2016) Loop Plume A B EDPS A nearby red giant star potentially hosts a planet with a mass of up to 12 times that of Jupiter. L2 Puppis, a solar analogue five billion years more evolved than the Sun, could give a hint to the future of the Solar System’s planets. Using ALMA, Pierre Kervella has observed L2 Puppis in molecular lines and continuum emission, finding a secondary source that is roughly 2 au away from the primary. This secondary source could be a giant planet or, alternatively, a brown dwarf as massive as 28 Jupiter masses. Further observations in ALMA bands 9 or 10 (λ ≈ 0.3–0.5 mm) can help to constrain the companion’s mass. If confirmed as a planet, it would be the first planet around an asymptotic giant branch star. L2 Puppis (A in the figure) is encircled by an edge-on circumstellar dust disk (inner disk shown in blue; surrounding dust in orange), which raises the question of whether the companion body is pre-existing, or if it has formed recently due to accretion processes within the disk. If pre-existing, the putative planet would have had an orbit similar in extent to that of Mars. Evolutionary models show that eventually this planet will be pulled inside the convective envelope of L2 Puppis by tidal forces. The companion’s interaction with the star’s circumstellar disk has invoked pronounced features above the disk: an extended loop of warm dusty material, and a visible plume, potentially launched by accretion onto a disk of material around the planet itself (B in the figure).
    [Show full text]
  • Jsolated Stars of Low Metallicity
    galaxies Article Jsolated Stars of Low Metallicity Efrat Sabach Department of Physics, Technion—Israel Institute of Technology, Haifa 32000, Israel; [email protected] Received: 15 July 2018; Accepted: 9 August 2018; Published: 15 August 2018 Abstract: We study the effects of a reduced mass-loss rate on the evolution of low metallicity Jsolated stars, following our earlier classification for angular momentum (J) isolated stars. By using the stellar evolution code MESA we study the evolution with different mass-loss rate efficiencies for stars with low metallicities of Z = 0.001 and Z = 0.004, and compare with the evolution with solar metallicity, Z = 0.02. We further study the possibility for late asymptomatic giant branch (AGB)—planet interaction and its possible effects on the properties of the planetary nebula (PN). We find for all metallicities that only with a reduced mass-loss rate an interaction with a low mass companion might take place during the AGB phase of the star. The interaction will most likely shape an elliptical PN. The maximum post-AGB luminosities obtained, both for solar metallicity and low metallicities, reach high values corresponding to the enigmatic finding of the PN luminosity function. Keywords: late stage stellar evolution; planetary nebulae; binarity; stellar evolution 1. Introduction Jsolated stars are stars that do not gain much angular momentum along their post main sequence evolution from a companion, either stellar or substellar, thus resulting with a lower mass-loss rate compared to non-Jsolated stars [1]. As previously stated in Sabach and Soker [1,2], the fitting formulae of the mass-loss rates for red giant branch (RGB) and asymptotic giant branch (AGB) single stars are set empirically by contaminated samples of stars that are classified as “single stars” but underwent an interaction with a companion early on, increasing the mass-loss rate to the observed rates.
    [Show full text]
  • Evolution of Thermally Pulsing Asymptotic Giant Branch Stars
    The Astrophysical Journal, 822:73 (15pp), 2016 May 10 doi:10.3847/0004-637X/822/2/73 © 2016. The American Astronomical Society. All rights reserved. EVOLUTION OF THERMALLY PULSING ASYMPTOTIC GIANT BRANCH STARS. V. CONSTRAINING THE MASS LOSS AND LIFETIMES OF INTERMEDIATE-MASS, LOW-METALLICITY AGB STARS* Philip Rosenfield1,2,7, Paola Marigo2, Léo Girardi3, Julianne J. Dalcanton4, Alessandro Bressan5, Benjamin F. Williams4, and Andrew Dolphin6 1 Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA 2 Department of Physics and Astronomy G. Galilei, University of Padova, Vicolo dell’Osservatorio 3, I-35122 Padova, Italy 3 Osservatorio Astronomico di Padova—INAF, Vicolo dell’Osservatorio 5, I-35122 Padova, Italy 4 Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195, USA 5 Astrophysics Sector, SISSA, Via Bonomea 265, I-34136 Trieste, Italy 6 Raytheon Company, 1151 East Hermans Road, Tucson, AZ 85756, USA Received 2016 January 1; accepted 2016 March 14; published 2016 May 6 ABSTRACT 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.
    [Show full text]
  • Isotopic Imprints of Super-Agb Stars and Their Supernovae in the Solar System
    82nd Annual Meeting of The Meteoritical Society 2019 (LPI Contrib. No. 2157) 6424.pdf ISOTOPIC IMPRINTS OF SUPER-AGB STARS AND THEIR SUPERNOVAE IN THE SOLAR SYSTEM. L. R. Nittler, Dept. of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Rd NW, Washington DC 20015, USA ([email protected]) Introduction: In studies of the origin of presolar grains and bulk nucleosynthetic isotopic anomalies in meteorites, little attention has been paid to the potential importance of stars in the mass range of ~8-10 solar masses. These stars lie in a middle-ground between low- and intermediate mass asymptotic giant branch (AGB) stars that end their lives as white dwarfs and massive stars whose cores burn all the way to Fe before collapsing and exploding as supernovae (SNII), leaving behind neutron stars or black holes. They evolve through a “super-AGB” phase, undergoing thousands of thermal pulses and losing most of their mass in strong winds [1]. However, their final fates (e.g., as white dwarfs versus neutron stars following core-collapse supernovae) depend on highly uncertain physics and diagnostic observable signatures of both super-AGB stars and their possible supernovae are controversial [1, 2]. Here we discuss possible ways super-AGB stars and their supernovae may have left nucleosynthetic imprints in the solar system. Super-AGB stars: Although most presolar SiC, silicate and oxide stardust grains are inferred to have originated in AGB stars [3], the isotopic signatures largely point to relatively low-mass (~1-3 M) progenitors. Until recently, intermediate-mass (4-8M) AGB stars have largely been ruled out as parent stars because their predicted O isotopic ratios are not observed.
    [Show full text]
  • The Coolest Brown Dwarfs
    ClassY - The Coolest Brown Dwarfs CFBDS J005910.90-011401.3 – T9/Y0 - first class Y, 30 light-years distance, Temp 620K, Mass 15-30 M_Jup WISE 0855−0714 – Y2 - coolest at Temp ~ 250K, 7.3 light-years distance, Mass 3-10 M_Jup ClassY - The Coolest Brown Dwarfs CFBDS J005910.90-011401.3 – T9/Y0 - first class Y, 30 light-years distance, Temp 620K, Mass 15-30 M_Jup WISE 0855−0714 – Y2 - coolest at Temp ~ 250K, 7.3 light-years distance, Mass 3-10 M_Jup Why are all brown dwarf stars about the same size, even if the mass ranges from 10-500 M_Jup? Stellar evolution so far Different energy sources during different stages in the star's evolution Protostar phase (KH contraction) MS phase H->He RGB phase (shell H->He) And remember: more massive stars evolve faster during all stages What is this Plot Showing? globular cluster Announcements • Today – More low mass stellar evolution • Thursday – High mass stellar evolution and HW#4 is due • Tuesday Feb 25 – Review • Thursday Feb 27 – Exam#1 Intrinsic variability • Those that vary in brightness as a result of conditions within the star itself. • Found in the instability strip. Any star within these portions of the H-R diagram will become unstable to pulsations. • The different regions produce different kinds of observed phenomena. • Stars may go through these stages several times during their lives. Cause of pulsations • Stars are variable because they are unstable in one way or another: they lack hydrostatic equilibrium beneath surface. • Miras are not well understood, but other, more periodically varying stars are better understood, like the Cepheids: • The ionization zone of He lies at a distance from the center of the star, close to the surface.
    [Show full text]
  • Variability Morphologies in the Color-Magnitude Diagram
    Variability Morphologies In The Color‐Magnitude Diagram Searching For Secular Variability Maxime Spano, Nami Mowlavi, Laurent Eyer, Gilbert Burki Geneva Observatory, University of Geneva, 51 Chemin des Maillettes, CH-1290 Sauverny, Switzerland Abstract. This work is part of an effort to detect secular variable objects in large scale surveys by analysing their path in color‐magnitude diagrams. To this aim, we first present the variability morphologies in the V/V‐I diagram of several types of variable stars. They comprise both periodic and non periodic variable stars from the Large Magellanic Cloud, such as classical Cepheids, long period variables or Be and R Coronae Borealis stars, as well as two of the detected secular variable stars in the Galaxy, FG Sge and V4334 Sgr. The study of the different variability morphologies allows the identification of regions in the color‐magnitude diagram where those secular variable stars could be detected. We also estimate the number of such secular variable stars expected in the Large Magellanic Cloud. Keywords: color-magnitude diagram; individual: FG Sge, V4334 Sgr, LMC. PACS: 97.10.Zr; 97.10.Sw; 98.56.Si. INTRODUCTION nearby galaxies are thus favored. OGLE‐II and III surveys of the LMC, providing BVI photometry for At some evolutionary phases, the stellar evolution resp. 7 and 35 millions stars (Udalski et al. 1997, timescale becomes comparable to the human lifetime. Udalski et al. 2000, Szymański 2005, Udalski et al. The evolution of these stars, called secular variable 2008) have been chosen here. All the variable stars stars, then becomes detectable in real time, providing a identified so far in the OGLE database are plotted in unique way to directly compare observations with the V/V‐I CMD shown in Fig.
    [Show full text]
  • U Antliae — a Dying Carbon Star
    THE BIGGEST, BADDEST, COOLEST STARS ASP Conference Series, Vol. 412, c 2009 Donald G. Luttermoser, Beverly J. Smith, and Robert E. Stencel, eds. U Antliae — A Dying Carbon Star William P. Bidelman,1 Charles R. Cowley,2 and Donald G. Luttermoser3 Abstract. U Antliae is one of the brightest carbon stars in the southern sky. It is classified as an N0 carbon star and an Lb irregular variable. This star has a very unique spectrum and is thought to be in a transition stage from an asymptotic giant branch star to a planetary nebula. This paper discusses possi- ble atomic and molecular line identifications for features seen in high-dispersion spectra of this star at wavelengths from 4975 A˚ through 8780 A.˚ 1. Introduction U Antliae (U Ant = HR 4153 = HD 91793) is classified as an N0 carbon star with a visual magnitude of 5.38 and B−V of +2.88 (Hoffleit 1982). It also is classified as an Lb irregular variable with small scale light variations. Scattered light optical images for U Ant have been made and these observations are consistent the existence of a geometrically thin (∼3 arcsec) spherically symmetric shell of radius ∼43 arcsec. The size of this shell agrees very well with that of the detached shell seen in CO radio line emission. These observations also show the presence of at least one, possibly two, shells inside the 43 arcsec shell (Gonz´alez Delgado et al. 2001). In this paper, absorption lines in the optical spectrum of U Ant are tentatively identified for this bright cool carbon star.
    [Show full text]
  • Evolution of Stars
    Evolution of Stars (Part I: Solar-type stars) 1 Death of the Sun Parts I and II 2 Learning goals: Be able to …. ! summarize the future of the Sun on a rough timescale; ! apply the basics of the conservation of energy and the battle between gravity and outward pressure to what “drives” a star to evolve at each major stage of evolution; ! explain what is meant by main sequence, subgiant, red giant branch, electron degeneracy, helium flash, horizontal branch, asymptotic giant branch, planetary nebula, white dwarf. 3 Be able to summarize the future of the Sun in a rough timescale. Apply the basics of the conservation of energy and the battle between gravely and pressure to what “drives” a star to evolve at each major stage of evolution. Explain what is meant by red giant branch, electron degeneracy, helium flash, horizontal branch, planetary nebula, white dwarf 4 5 http://chandra.harvard.edu/xray_sources/browndwarf_fg.html Brown Dwarf "In between a star and a planet "Jupiter < BD mass < 0.08 Sun "Radiates in infrared due to low temperature. "Mass too low to start fusion in core. "Slowly cools over trillions of years. 6 7 Core producing energy--Fusing H to He 8 A review of what we know the Sun is doing as a main-sequence star 9 Number of particles in core is decreasing. NET RESULT IN: 6 H OUT: 1 He + 2 H FUSION RATE MUST INCREASE TO OFFSET DECREASE IN PARTICLE PRESSURE! Sun is slowly becoming more and more luminous. 10 Explain how the Sun maintains a constant balance in its interior (solar thermostat) Part of the pressure depends on the number of particles Pressure decreases, core shrinks slightly, pressure evens out, fusion rate must increase to offset the smaller pressure provided by the number of particles present.
    [Show full text]
  • Stellar Evolution
    AccessScience from McGraw-Hill Education Page 1 of 19 www.accessscience.com Stellar evolution Contributed by: James B. Kaler Publication year: 2014 The large-scale, systematic, and irreversible changes over time of the structure and composition of a star. Types of stars Dozens of different types of stars populate the Milky Way Galaxy. The most common are main-sequence dwarfs like the Sun that fuse hydrogen into helium within their cores (the core of the Sun occupies about half its mass). Dwarfs run the full gamut of stellar masses, from perhaps as much as 200 solar masses (200 M,⊙) down to the minimum of 0.075 solar mass (beneath which the full proton-proton chain does not operate). They occupy the spectral sequence from class O (maximum effective temperature nearly 50,000 K or 90,000◦F, maximum luminosity 5 × 10,6 solar), through classes B, A, F, G, K, and M, to the new class L (2400 K or 3860◦F and under, typical luminosity below 10,−4 solar). Within the main sequence, they break into two broad groups, those under 1.3 solar masses (class F5), whose luminosities derive from the proton-proton chain, and higher-mass stars that are supported principally by the carbon cycle. Below the end of the main sequence (masses less than 0.075 M,⊙) lie the brown dwarfs that occupy half of class L and all of class T (the latter under 1400 K or 2060◦F). These shine both from gravitational energy and from fusion of their natural deuterium. Their low-mass limit is unknown.
    [Show full text]
  • Initiating Solar System Formation Through Stellar ° Shock Waves
    LPSC 155 XXTV / 0^ INITIATING SOLAR SYSTEM FORMATION THROUGH STELLAR ° SHOCK WAVES. A. P. Boss & E. A. Myhill, DTM, Carnegie Institution of Washing- ton, 5241 Broad Branch Road N.W., Washington DC 20015. Isotopic anomalies in presolar grains and other meteoritical components require nu- cleosynthesis in stellar interiors, condensation into dust grains in stellar envelopes, trans- port of the grains through the interstellar medium by stellar outflows, and finally injection of the grains into the presolar nebula. The proximity of the presolar cloud to these ener- getic stellar events suggests that a shock wave from a stellar outflow might have initiated the collapse of an otherwise stable presolar cloud. We have begun to study the interac- tions of stellar shock waves with thermally supported, dense molecular cloud cores, using ./ a three spatial dimension (3D) radiative hydrodynamics code. Supernova shock waves "**--. have been shown by others to destroy quiescent clouds, so we are trying to determine if the much smaller shock speeds found in, e.g., asymptotic giant branch (AGB) star winds, are strong enough to initiate collapse in an otherwise stable, rotating, solar-mass cloud /' core, without leading to destruction of the cloud. ^ INTRODUCTION. The presence of noble gas isotopic anomalies in presolar SiC grains seems to require nucleosynthesis in a red giant star [1,2,3] and subsequent ejection of the products in the strong stellar wind that accompanies the asymptotic giant branch (AGB) phase of stellar evolution. A few SiC grains have C, N, and Si isotopic abundances quite different from the majority, possibly requiring their production in a supernova explosion [4].
    [Show full text]