DOCSLIB.ORG

Astronomy 110 Announcements: Life and Death of a Low Mass Star Stages

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Astronomy 110 Announcements: Life and Death of a Low Mass Star Stages Astronomy 110 Announcements: Life and Death of a Low Mass Star Stages: • No reading quiz today 2 1. H-burning main sequence • Homework #3 due at start of class 1 • Pick up Homework #4 in front of class (due 3 2. H-shell burning next Wednesday, June 22nd) Red Giant • Reading for Monday: pp. 330 – 345 3. He burning star 4 (schedule has been updated for rest of year 4. Double shell on website) burning star 6 5. Planetary Nebula 5 6. White Dwarf Stage #2: Red Giant Stage #2: Red Giant (H-burning shell, inert He core) (H-burning shell, inert He core) • After 10 billion years, sun’s core H is used up • Inert He core (not hot enough to burn yet) • He core shrinks with surrounding layers • Surrounding shell of H gets hot enough for fusion • H shell burning goes at rapid pace! more energy than during main sequence • Star expands and cools: Red Giant Phase Hydrogen core burning Hydrogen shell burning Stage #2: Red Giant (H-burning shell, inert He core) The “Broken Thermostat” • During MS, temp & size regulated by solar thermostat • During H-shell burning, no thermostat • H-shell burning makes more Helium fusion requires higher temperatures than hydrogen He, dumped onto core fusion because larger charge leads to greater repulsion • Core contracts further due to increased weight Fusion of two helium nuclei doesn’t work, so helium fusion • H-shell burning accelerates • Sun grows to 100 times its must combine three He nuclei to make carbon ! “Triple size Alpha Process” Stage #3: Helium burning star Helium Flash • Thermostat is broken in low-mass red giant because degeneracy pressure supports core • Core temperature rises rapidly when helium fusion begins • Helium fusion rate skyrockets until thermal pressure takes over and expands core again Helium burning stars neither shrink nor grow because thermostat is temporarily fixed. Question Question What happens when the star’s core runs out of helium? What happens when the star’s core runs out of helium? A. The star explodes B. Carbon fusion begins A. The star explodes C. The core cools off B. Carbon fusion begins D. Helium fuses in a shell around the core C. The core cools off D. Helium fuses in a shell around the core Stage #4: Double-shell burning star Stage #5: Planetary Nebula A low mass star dies by shedding its outer layers • Similar to the red giant phase: – Inert Carbon core – Surrounding shells: burning H and He • Star becomes very cool and luminous, expanding in size • Gravity is very weak at stellar surface leading to mass loss through a strong stellar wind (stage #5) • Continuing contraction of core leads to greater & greater luminosity, however, it never gets hot enough to fuse carbon • Star collapses to a dense, small, hot object: white dwarf Stage #6: White Dwarf Life stages The central remaining core is very hot, leading to of a low- ionization of the surrounding gas shell. mass star like the Sun Star clusters White dwarfs help us test cool off and models of grow dimmer stellar with time evolution because they contain stars of same age but at different life stages White dwarfs shrink when you add mass to them because A white dwarf is about the same size as Earth their gravity gets stronger The White Dwarf Limit Shrinkage of White Dwarfs Einstein’s theory of relativity says • Quantum mechanics says that electrons in the that nothing can move faster than same place cannot be in the same state light • Adding mass to a white dwarf increases its When electron speeds in white gravity, forcing electrons into a smaller space dwarf approach speed of light, electron degeneracy pressure can • In order to avoid being in the same state some of no longer support it the electrons need to move faster Chandrasekhar found (at age 20!) • Is there a limit to how much you can shrink a that this happens when a white white dwarf? dwarf’s mass reaches S. Chandrasekhar 1.4 MSun 12.3 Life as a High-Mass Star • Our Goals for Learning • What are the life stages of a high mass star? What are the life stages of a high • How do high-mass stars make the elements mass star? necessary for life? • How does a high-mass star die? High-Mass Stars > 8 MSun High-Mass Star’s Life Intermediate- Mass Stars Early stages are similar to those of low-mass star: • Main Sequence: H fuses to He in core Low-Mass Stars < 2 M • Red Supergiant: H fuses to He in shell around Sun inert He core • Helium Core Burning: He fuses to C in core (no He flash because core temp is high and sustains Brown Dwarfs thermal pressure—no degeneracy) IN 4 protons OUT 4He nucleus 2 gamma rays 2 positrons 2 neutrinos Total mass is 0.7% lower Review: Proton-proton chain is how hydrogen fuses into helium in Sun. High Mass Stars also fuse H ! He, but with CNO cycle High-mass stars become CNO cycle is just supergiants after another way to fuse H core H runs into He, using carbon, out nitrogen, and oxygen as catalysts Luminosity CNO cycle is main doesn’t mechanism for H fusion change much in high mass stars but radius gets because core far larger temperature is higher How do high mass stars make the elements necessary for life? Big Bang made 75% H, 25% He – stars make everything else Helium fusion can make carbon in low-mass stars Helium-capture reactions add two protons at a time CNO cycle can change C into N and O Advanced nuclear fusion reactions require extremely high temperatures Only high-mass stars can attain high enough core temperatures before degeneracy pressure stops contraction Helium capture builds C into O, Ne, Mg, … Advanced nuclear burning occurs in multiple shells Advanced reactions make heavier elements (“layers of an onion”) Iron is dead Evidence for end for fusion helium because nuclear capture: reactions involving iron Higher do not release abundances of energy elements with even numbers (Fe has lowest of protons mass per nuclear particle) Death of High Mass Star • Left with inert iron (Fe) core. • Briefly supported by electron degeneracy pressure. • Outer shells still burning and dumping tremendous amounts of mass onto the core. • Gravity overcomes the electron degeneracy and squishes the protons and electrons together, yielding neutrons. How does a high mass star die? Core degeneracy Neutron Star pressure goes away • Original core mass ~ 10 Msun, and size is ~1 REarth. because electrons Collapses to only a few kilometers in size! combine with protons, making neutrons and neutrinos Neutrons collapse to the center, forming a neutron star Death of High Mass Star • Neutron star has its own degeneracy pressure that can stop the collapse • If the star is too massive, nothing can stop collapse ! Black Hole • Generation of neutrons gives off extreme amounts of neutrinos that produce a shock wave, sending the outer layers of the star off at a furious pace. • Supernova explosion! • Brighter than 10 billion Suns for a few days Energy and neutrons released in supernova explosion enables elements heavier than iron to form Iron builds up in core until degeneracy pressure can no longer resist gravity Elements made Core then during suddenly supernova collapses, explosion creating supernova explosion before after Supernova 1987A is the nearest supernova observed in the last 400 years Crab Nebula: Remnant of supernova observed in 1054 A.D. 12.4 Summary of Stellar Lives The next nearby • Our Goals for Learning supernova? • How does a star’s mass determine its life story? • How are the lives of stars with close companions different? Low-Mass Star Summary 1. Main Sequence: H fuses to He in core 2. Red Giant: H fuses to He in shell How does a star’s mass around He core 3. Helium Core Burning: determine its life story? He fuses to C in core while H fuses to He in shell 4. Double Shell Burning: H and He both fuse in shells 5. Planetary Nebula leaves white Not to scale! dwarf behind Life Stages of High-Mass Star Reasons for Life Stages 1. Main Sequence: H fuses to He in " Core shrinks and heats until it’s core hot enough for fusion 2. Red Supergiant: H fuses to He in " Nuclei with larger charge shell around He core require higher temperature for fusion 3. Helium Core Burning: He fuses to C in core while H " Core thermostat is broken fuses to He in shell while core is not hot enough for fusion (shell burning) 4. Multiple Shell Burning: Many elements fuse in shells " Core fusion can’t happen if degeneracy pressure keeps core 5. Supernova leaves neutron star from shrinking Not to scale! Not to scale! behind Life of a 20 MSun star Life of a 1 MSun star.
Load more

Recommended publications
  • Collapsars As a Major Source of R-Process Elements
    Collapsars as a major source of r-process elements Daniel M. Siegel1;2;3;4;5, Jennifer Barnes1;2;5 & Brian D. Metzger1;2 1Department of Physics, Columbia University, New York, NY, USA 2Columbia Astrophysics Laboratory, Columbia University, New York, NY, USA 3Perimeter Institute for Theoretical Physics, Waterloo, Ontario, Canada 4Department of Physics, University of Guelph, Guelph, Ontario, Canada 5NASA Einstein Fellow The production of elements by rapid neutron capture (r-process) in neutron-star mergers is expected theoretically and is supported by multimessenger observations1–3 of gravitational- wave event GW170817: this production route is in principle sufficient to account for most of the r-process elements in the Universe4. Analysis of the kilonova that accompanied GW170817 identified5, 6 delayed outflows from a remnant accretion disk formed around the newly born black hole7–10 as the dominant source of heavy r-process material from that event9, 11. Sim- ilar accretion disks are expected to form in collapsars (the supernova-triggering collapse of rapidly rotating massive stars), which have previously been speculated to produce r-process elements12, 13. Recent observations of stars rich in such elements in the dwarf galaxy Retic- arXiv:1810.00098v2 [astro-ph.HE] 14 Aug 2020 ulum II14, as well as the Galactic chemical enrichment of europium relative to iron over longer timescales15, 16, are more consistent with rare supernovae acting at low stellar metal- licities than with neutron-star mergers. Here we report simulations that show that collapsar accretion disks yield sufficient r-process elements to explain observed abundances in the Uni- 1 verse. Although these supernovae are rarer than neutron- star mergers, the larger amount of material ejected per event compensates for the lower rate of occurrence.
    [Show full text]
  • The Centrality of the Holy Sacrifice of the Mass at Christendom College
    THE CENTRALITY OF THE HOLY SACRIFICE OF THE MASS AT CHRISTENDOM COLLEGE The Church teaches that the Eucharist is “the source and summit of the Christian life”1 and that the celebration of the Mass “is a sacred action surpassing all others. No other action of the Church can equal its efficacy.”2 That is why “as a natural expression of the Catholic identity of the University. members of this community . will be encouraged to participate in the celebration of the sacraments, especially the Eucharist, as the most perfect act of community worship.”3 Those central truths are taught and lived at Christendom College, a “Catholic coeducational college institutionally committed to the Magisterium”4 of the Church, in the following ways: The Celebration of the Sacred Liturgy The Holy Sacrifice of the Mass • Mass is offered frequently: twice daily Monday through Thursday, three times on MONDAY (Friday), twice on Saturday, and once on Sunday (the day on which we gather as one family). • Mass in the Roman Rite is celebrated in all the ways offered by the Church: in the Ordinary Form in both English and Latin, and in the Extraordinary Form from one to three times per week, as circumstances permit. • The Ordinary Form of the Mass is celebrated with the solemnity appropriate to each feast, utilizing worthy sacred vessels and vestments, and drawing upon the Church’s rich tradition of chant, polyphony, and hymnody. • The Ordinary Form of the Mass is celebrated reverently and with rubrical fidelity. • No classes or other activities are scheduled during Mass times. • The majority of the College community attends daily Mass regularly and with great devotion.
    [Show full text]
  • SHELL BURNING STARS: Red Giants and Red Supergiants
    SHELL BURNING STARS: Red Giants and Red Supergiants There is a large variety of stellar models which have a distinct core – envelope structure. While any main sequence star, or any white dwarf, may be well approximated with a single polytropic model, the stars with the core – envelope structure may be approximated with a composite polytrope: one for the core, another for the envelope, with a very large difference in the “K” constants between the two. This is a consequence of a very large difference in the specific entropies between the core and the envelope. The original reason for the difference is due to a jump in chemical composition. For example, the core may have no hydrogen, and mostly helium, while the envelope may be hydrogen rich. As a result, there is a nuclear burning shell at the bottom of the envelope; hydrogen burning shell in our example. The heat generated in the shell is diffusing out with radiation, and keeps the entropy very high throughout the envelope. The core – envelope structure is most pronounced when the core is degenerate, and its specific entropy near zero. It is supported against its own gravity with the non-thermal pressure of degenerate electron gas, while all stellar luminosity, and all entropy for the envelope, are provided by the shell source. A common property of stars with well developed core – envelope structure is not only a very large jump in specific entropy but also a very large difference in pressure between the center, Pc, the shell, Psh, and the photosphere, Pph. Of course, the two characteristics are closely related to each other.
    [Show full text]
  • Understanding When to Kneel, Sit and Stand at a Traditional Latin Mass
    UNDERSTANDING WHEN TO KNEEL, SIT AND STAND AT A TRADITIONAL LATIN MASS __________________________ A Short Essay on Mass Postures __________________________ by Richard Friend I. Introduction A Catholic assisting at a Traditional Latin Mass for the first time will most likely experience bewilderment and confusion as to when to kneel, sit and stand, for the postures that people observe at Traditional Latin Masses are so different from what he is accustomed to. To understand what people should really be doing at Mass is not always determinable from what people remember or from what people are presently doing. What is needed is an understanding of the nature of the liturgy itself, and then to act accordingly. When I began assisting at Traditional Latin Masses for the first time as an adult, I remember being utterly confused with Mass postures. People followed one order of postures for Low Mass, and a different one for Sung Mass. I recall my oldest son, then a small boy, being thoroughly amused with the frequent changes in people’s postures during Sung Mass, when we would go in rather short order from standing for the entrance procession, kneeling for the preparatory prayers, standing for the Gloria, sitting when the priest sat, rising again when he rose, sitting for the epistle, gradual, alleluia, standing for the Gospel, sitting for the epistle in English, rising for the Gospel in English, sitting for the sermon, rising for the Credo, genuflecting together with the priest, sitting when the priest sat while the choir sang the Credo, kneeling when the choir reached Et incarnatus est etc.
    [Show full text]
  • A Comparison of the Two Forms of the Roman Rite
    A Comparison of the Two Forms of the Roman Rite Mass Structures Orientation Language The purpose of this presentation is to prepare you for what will very likely be your first Traditional Latin Mass (TLM). This is officially named “The Extraordinary Form of the Roman Rite.” We will try to do that by comparing it to what you already know - the Novus Ordo Missae (NOM). This is officially named “The Ordinary Form of the Roman Rite.” In “Mass Structures” we will look at differences in form. While the TLM really has only one structure, the NOM has many options. As we shall see, it has so many in fact, that it is virtually impossible for the person in the pew to determine whether the priest actually performs one of the many variations according to the rubrics (rules) for celebrating the NOM. Then, we will briefly examine the two most obvious differences in the performance of the Mass - the orientation of the priest (and people) and the language used. The orientation of the priest in the TLM is towards the altar. In this position, he is facing the same direction as the people, liturgical “east” and, in a traditional church, they are both looking at the tabernacle and/or crucifix in the center of the altar. The language of the TLM is, of course, Latin. It has been Latin since before the year 400. The NOM was written in Latin but is usually performed in the language of the immediate location - the vernacular. [email protected] 1 Mass Structure: Novus Ordo Missae Eucharistic Prayer Baptism I: A,B,C,D Renewal Eucharistic Prayer II: A,B,C,D Liturgy of Greeting: Penitential Concluding Dismissal: the Word: A,B,C Rite: A,B,C Eucharistic Prayer Rite: A,B,C A,B,C Year 1,2,3 III: A,B,C,D Eucharistic Prayer IV: A,B,C,D 3 x 4 x 3 x 16 x 3 x 3 = 5184 variations (not counting omissions) Or ~ 100 Years of Sundays This is the Mass that most of you attend.
    [Show full text]
  • Low Requiem Mass
    REQUIEM LOW MASS FOR TWO SERVERS The Requiem Mass is very ancient in its origin, being the predecessor of the current Roman Rite (i.e., the so- called “Tridentine Rite”) of Mass before the majority of the gallicanizations1 of the Mass were introduced. And so, many ancient features, in the form of omissions from the normal customs of Low Mass, are observed2. A. Interwoven into the beautiful and spiritually consoling Requiem Rite is the liturgical principle, that all blessings are reserved for the deceased soul(s) for whose repose the Mass is being celebrated. This principle is put into action through the omission of these blessings: 1. Holy water is not taken before processing into the Sanctuary. 2. The sign of the Cross is not made at the beginning of the Introit3. 3. C does not kiss the praeconium4 of the Gospel after reading it5. 4. During the Offertory, the water is not blessed before being mixed with the wine in the chalice6. 5. The Last Blessing is not given. B. All solita oscula that the servers usually perform are omitted, namely: . When giving and receiving the biretta. When presenting and receiving the cruets at the Offertory. C. Also absent from the Requiem Mass are all Gloria Patris, namely during the Introit and the Lavabo. D. The Preparatory Prayers are said in an abbreviated form: . The entire of Psalm 42 (Judica me) is omitted; consequently the prayers begin with the sign of the Cross and then “Adjutorium nostrum…” is immediately said. After this, the remainder of the Preparatory Prayers are said as usual.
    [Show full text]
  • Astro 404 Lecture 30 Nov. 6, 2019 Announcements
    Astro 404 Lecture 30 Nov. 6, 2019 Announcements: • Problem Set 9 due Fri Nov 8 2 3/2 typo corrected in L24 notes: nQ = (2πmkT/h ) • Office Hours: Instructor – after class or by appointment • TA: Thursday noon-1pm or by appointment • Exam: grading elves hard at work Last time: low-mass stars after main sequence Q: burning phases? 1 Q: shell burning “mirror” principle? Low-Mass Stars After Main Sequence unburnt H ⋆ helium core contracts H He H burning in shell around core He outer layers expand → red giant “mirror” effect of shell burning: • core contraction, envelope expansion • total gravitational potential energy Ω roughly conserved core becomes more tightly bound, envelope less bound ⋆ helium ignition degenerate core unburnt H H He runaway burning: helium flash inert He → 12 He C+O 2 then core helium burning 3α C and shell H burning “horizontal branch” star unburnt H H He ⋆ for solar mass stars: after CO core forms inert He He C • helium shell burning begins inert C • hydrogen shell burning continues Q: star path on HR diagram during these phases? 3 Low-Mass Post-Main-Sequence: HR Diagram ⋆ H shell burning ↔ red giant ⋆ He flash marks “tip of the red giant branch” ⋆ core He fusion ↔ horizontal branch ⋆ He + H shell burning ↔ asymptotic giant branch asymptotic giant branch H+He shell burn He flash core He burn L main sequence horizontal branch red giant branch H shell burning Sun Luminosity 4 Temperature T iClicker Poll: AGB Star Intershell Region in AGB phase: burning in two shells, no core fusion unburnt H H He inert He He C Vote your conscience–all
    [Show full text]
  • Master of Ceremonies for High Mass (Missa Cantata)
    MASTER OF CEREMONIES FOR HIGH MASS (MISSA CANTATA) REQUIREMENTS AND EXPECTATIONS OF A MASTER OF CEREMONIES A master of ceremonies (MC) must be what his title entails: the master, or expert, on the liturgical ceremonies. Hence, he must not only fully know the positions of the inferior ministers at High Mass, but also be acquainted with the celebrant’s actions. Additionally, the MC should have a thorough understanding of the general principles of the Roman Rite,1 be acquainted with the various liturgical books,2 the liturgical office of the schola and how it affects the MC’s position,3 and of course, the layout and preparation of the missal. The MC must also know how to correct a problematic situation with tact and discretion; this is especially true when advising the celebrant (C). In dealing with the servers, any corrections made (especially from a distance) should be as inconspicuous as possible. For minor matters, it is often better to simply let the matter pass and address it later outside of the ceremony in the sacristy. CONCERNING THE ORGANIZATION OF THE PREPARATIONS BEFORE MASS The MC must oversee all of the preparations that are necessary before the beginning of Mass. You must ensure they are done correctly and on time so that Mass may start as scheduled. As MC, you should remain the sacristy as much as possible, directing the preparations from there (there should be a permanent duties checklist in the sacristy assigning each server a specific duty to complete before Mass). In this way, you can ensure the servers are keeping silence in the sacristy, are organized and that any last minute details can be taken care of easily (such as replacing late servers).
    [Show full text]
  • Minicourses in Astrophysics, Modular Approach, Vol
    DOCUMENT RESUME ED 161 706 SE n325 160 ° TITLE Minicourses in Astrophysics, Modular Approach, Vol.. II. INSTITUTION Illinois Univ., Chicago. SPONS AGENCY National Science Foundation, Washington, D. BUREAU NO SED-75-21297 PUB DATE 77 NOTE 134.,; For related document,. see SE 025 159; Contains occasional blurred,-dark print EDRS PRICE MF-$0.83 HC- $7..35 Plus Postage. DESCRIPTORS *Astronomy; *Curriculum Guides; Evolution; Graduate 1:-Uldy; *Higher Edhcation; *InstructionalMaterials; Light; Mathematics; Nuclear Physics; *Physics; Radiation; Relativity: Science Education;. *Short Courses; Space SCiences IDENTIFIERS *Astrophysics , , ABSTRACT . This is the seccA of a two-volume minicourse in astrophysics. It contains chaptez:il on the followingtopics: stellar nuclear energy sources and nucleosynthesis; stellarevolution; stellar structure and its determinatioli;.and pulsars.Each chapter gives much technical discussion, mathematical, treatment;diagrams, and examples. References are-included with each chapter.,(BB) e. **************************************t****************************- Reproductions supplied by EDRS arethe best-that can be made * * . from the original document. _ * .**************************4******************************************** A U S DEPARTMENT OF HEALTH. EDUCATION &WELFARE NATIONAL INSTITUTE OF EDUCATION THIS DOCUMENT AS BEEN REPRO' C'')r.EC! EXACTLY AS RECEIVED FROM THE PERSON OR ORGANIZATION'ORIGIkl A TINC.IT POINTS OF VIEW OR OPINIONS aft STATED DO NOT NECESSARILY REPRE SENT OFFICIAL NATIONAL INSTITUTE Of EDUCATION POSITION OR POLICY s. MINICOURSES IN ASTROPHYSICS MODULAR APPROACH , VOL. II- FA DEVELOPED'AT THE hlIVERSITY OF ILLINOIS AT CHICAGO 1977 I SUPPORTED BY NATIONAL SCIENCE FOUNDATION DIRECTOR: S. SUNDARAM 'ASSOCIATETIRECTOR1 J. BURNS _DEPARTMENT OF PHYSICS. DEPARTMENT OF PHYSICS AND SPACE UNIVERSITY OF ILLINOIS SCIENCES CHICAGO, ILLINOIS 60680 FLORIDA INSTITUTE OF TECHNOLOGY MELBOURNE, FLORIDA 32901 0 0 4, STELLAR NUCLEAR ENERGY SOURCES and NUCLEGSYNTHESIS 'I.
    [Show full text]
  • Discovery of a Low-Mass Companion to a Metal-Rich F Star with the Marvels Pilot Project
    The Astrophysical Journal, 718:1186–1199, 2010 August 1 doi:10.1088/0004-637X/718/2/1186 C 2010. The American Astronomical Society. All rights reserved. Printed in the U.S.A. DISCOVERY OF A LOW-MASS COMPANION TO A METAL-RICH F STAR WITH THE MARVELS PILOT PROJECT Scott W. Fleming1,JianGe1, Suvrath Mahadevan1,2,3, Brian Lee1, Jason D. Eastman4, Robert J. Siverd4, B. Scott Gaudi4, Andrzej Niedzielski5, Thirupathi Sivarani6, Keivan G. Stassun7,8, Alex Wolszczan2,3, Rory Barnes9, Bruce Gary7, Duy Cuong Nguyen1, Robert C. Morehead1, Xiaoke Wan1, Bo Zhao1, Jian Liu1, Pengcheng Guo1, Stephen R. Kane1,10, Julian C. van Eyken1,10, Nathan M. De Lee1, Justin R. Crepp1,11, Alaina C. Shelden1,12, Chris Laws9, John P. Wisniewski9, Donald P. Schneider2,3, Joshua Pepper7, Stephanie A. Snedden12, Kaike Pan12, Dmitry Bizyaev12, Howard Brewington12, Olena Malanushenko12, Viktor Malanushenko12, Daniel Oravetz12, Audrey Simmons12, and Shannon Watters12,13 1 Department of Astronomy, University of Florida, 211 Bryant Space Science Center, Gainesville, FL 326711-2055, USA; scfl[email protected]fl.edu 2 Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802, USA 3 Center for Exoplanets and Habitable Worlds, The Pennsylvania State University, University Park, PA 16802, USA 4 Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA 5 Torun´ Center for Astronomy, Nicolaus Copernicus University, ul. Gagarina 11, 87-100, Torun,´ Poland 6 Indian Institute of Astrophysics, Bangalore 560034, India 7 Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235, USA 8 Department of Physics, Fisk University, 1000 17th Ave.
    [Show full text]
  • The Core Helium Flash Revisited
    A&A 520, A114 (2010) Astronomy DOI: 10.1051/0004-6361/201014461 & c ESO 2010 Astrophysics The core helium flash revisited III. From Population I to Population III stars M. Mocák1,S.W.Campbell2,3,E.Müller4, and K. Kifonidis4 1 Institut d’Astronomie et d’Astrophysique, Université Libre de Bruxelles, CP 226, 1050 Brussels, Belgium e-mail: [email protected] 2 Departament de Física i Enginyeria Nuclear, EUETIB, Universitat Politécnica de Catalunya, C./Comte d’Urgell 187, 08036 Barcelona, Spain e-mail: [email protected] 3 Centre for Stellar and Planetary Astrophysics, School of Mathematical Sciences, Monash University, Melbourne 3800, Australia 4 Max-Planck-Institut für Astrophysik, Postfach 1312, 85741 Garching, Germany Received 18 March 2010 / Accepted 13 June 2010 ABSTRACT Context. Degenerate ignition of helium in low-mass stars at the end of the red giant branch phase leads to dynamic convection in their helium cores. One-dimensional (1D) stellar modeling of this intrinsically multi-dimensional dynamic event is likely to be inadequate. Previous hydrodynamic simulations imply that the single convection zone in the helium core of metal-rich Pop I stars grows during the flash on a dynamic timescale. This may lead to hydrogen injection into the core and to a double convection zone structure as known from one-dimensional core helium flash simulations of low-mass Pop III stars. Aims. We perform hydrodynamic simulations of the core helium flash in two and three dimensions to better constrain the nature of these events. To this end we study the hydrodynamics of convection within the helium cores of a 1.25 M metal-rich Pop I star (Z = 0.02), and, for the first time, a 0.85 M metal-free Pop III star (Z = 0) near the peak of the flash.
    [Show full text]
  • Announcements
    Announcements • Next Session – Stellar evolution • Low-mass stars • Binaries • High-mass stars – Supernovae – Synthesis of the elements • Note: Thursday Nov 11 is a campus holiday Red Giant 8 100Ro 10 years L 10 3Ro, 10 years Temperature Red Giant Hydrogen fusion shell Contracting helium core Electron Degeneracy • Pauli Exclusion Principle says that you can only have two electrons per unit 6-D phase- space volume in a gas. DxDyDzDpxDpyDpz † Red Giants • RG Helium core is support against gravity by electron degeneracy • Electron-degenerate gases do not expand with increasing temperature (no thermostat) • As the Temperature gets to 100 x 106K the “triple-alpha” process (Helium fusion to Carbon) can happen. Helium fusion/flash Helium fusion requires two steps: He4 + He4 -> Be8 Be8 + He4 -> C12 The Berylium falls apart in 10-6 seconds so you need not only high enough T to overcome the electric forces, you also need very high density. Helium Flash • The Temp and Density get high enough for the triple-alpha reaction as a star approaches the tip of the RGB. • Because the core is supported by electron degeneracy (with no temperature dependence) when the triple-alpha starts, there is no corresponding expansion of the core. So the temperature skyrockets and the fusion rate grows tremendously in the `helium flash’. Helium Flash • The big increase in the core temperature adds momentum phase space and within a couple of hours of the onset of the helium flash, the electrons gas is no longer degenerate and the core settles down into `normal’ helium fusion. • There is little outward sign of the helium flash, but the rearrangment of the core stops the trip up the RGB and the star settles onto the horizontal branch.
    [Show full text]