DOCSLIB.ORG

The Evolution and Nucleosynthesis of Thermally Pulsing Asymptotic Giant Branch Stars

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Evolution and Nucleosynthesis of Thermally Pulsing Asymptotic Giant Branch Stars The Evolution and Nucleosynthesis of Thermally Pulsing Asymptotic Giant Branch Stars Richard James Stancliffe Churchill College Institute of Astronomy University of Cambridge Thesis submitted for the Degree of Doctor of Philosophy at the University of Cambridge · 2005 · Declaration I hereby declare that my thesis entitled The Evolution and Nucleosynthesis of Thermally Pulsing Asymptotic Giant Branch Stars is not substantially the same as any that I have submitted for a degree or diploma or other qualification at any other University. I further state that no part of my thesis has already been or is being concurrently submitted for any such degree, diploma or other qualification. This dissertation is the result of my own work and includes nothing which is the outcome of work done in collaboration except where specifically indicated in the text. Those parts of this thesis which have been published or accepted for publication are as follows: • Material from chapters 2 and 3 has been published as: Stancliffe R. J., Tout C. A., Pols O. R., 2004, “Deep dredge-up in intermediate-mass thermally pulsing asymptotic giant branch stars”, Monthly Notices of the Royal Astronomical Society, 352, 984-992 and was completed in collaboration with these authors. • Material from chapter 4 has been published as: Stancliffe R. J., Izzard R. G., Tout C. A., 2005, “Third dredge-up in low-mass: solving the Large Magellanic Cloud carbon star mystery”, Monthly Notices of the Royal Astronomical Society, 356, L1-L5 and was completed in collaboration with these authors. • Material from chapter 5 has been published as: Stancliffe R. J., Lugaro M. A., Ugalde C., Tout C. A., G¨orres J., Wi- escher M., 2005, “The effect of the 19F(α, p)22Ne reaction rate uncer- tainty on the yield of fluorine from Wolf-Rayet stars”, Monthly Notices of the Royal Astronomical Society, 360, 375-379 and was completed in collaboration with these authors. This thesis contains fewer than 60,000 words. R. J. Stancliffe Cambridge, October 23, 2005 2 Abstract The thermally pulsing asymptotic giant branch (TP-AGB) is a computa- tionally demanding phase of evolution. This work presents a set of models that have been computed fully simultaneously – i.e. by solving the equations of stellar structure, nuclear burning and mixing together for each iteration of each timestep. It details the development of a viscous mesh technique in order to deal with some of the numerical problems that occur during the TP-AGB. Models have been created at solar metallicity (Z = 0.02) and metallici- ties appropriate to the Large and Small Magellanic Clouds (Z = 0.008 and Z = 0.004). These are evolved without mass loss. The solar metallicity models display important differences from those computed using other codes including deeper third dredge-up. The Large and Small Magellanic Cloud models are used to investigate the problem of the carbon star luminosity function. TP-AGB stars are also important sites for stellar nucleosynthesis. In or- der to investigate nucleosynthesis on the TP-AGB a set of subroutines have been developed to track the evolution of isotopes from deuterium to sulphur plus important iron group elements. These have been used to calculate the evolution of minor isotopes in TP-AGB stars of 1.5, 3 and 5 M at metal- licities of Z = 0.02, 0.008 and 0.004 evolved with mass loss. The results of these calculations are compared to known constraints from spectroscopic observations and measurements of pre-solar grains. At the end of the TP-AGB the star makes the transition to a white dwarf. In the course of trying to calculate this evolution it was found that numerical diffusion could substantially affect the evolution and that this phase has to be treated with great care. Contents Acknowledgments xi 1 Introduction 1 1.1 Stellar Evolution . 1 1.1.1 The Main-sequence . 1 1.1.2 The Red Giant Branch . 3 1.1.3 The Asymptotic Giant Branch . 5 1.2 A Brief History of the Thermally Pulsing Asymptotic Giant Branch . 6 1.2.1 The Discovery of Thermal Pulses . 6 1.2.2 Third Dredge-up . 10 1.3 TP-AGB Nucleosynthesis and the s-process . 12 1.3.1 Light Element Nucleosynthesis . 13 1.3.2 Nucleosynthesis via the s-process . 14 1.3.3 Mass Loss . 15 1.4 Observational Constraints . 17 1.4.1 Direct Observations . 17 1.4.2 Pre-solar Grains . 19 2 stars: a Stellar Evolution Code 21 i 2.1 Input Physics . 21 2.2 Implementation . 25 2.2.1 Convective Mixing and the Choice of σ . 26 2.3 Overview of the stars Code Structure . 27 2.4 Numerical Instability . 29 2.4.1 Mixing . 29 2.4.2 Viscous Mesh . 30 2.4.3 Timestep Control . 32 2.5 Making Stellar Models . 33 3 TP-AGB Stars of Solar Metallicity 35 3.1 Initial Attempt – a 5 M star . 35 3.2 General Properties . 38 3.3 Model-by-model . 38 3.3.1 1 M ............................ 39 3.3.2 1.5 M ........................... 40 3.3.3 2 M ............................ 41 3.3.4 3 M ............................ 43 3.3.5 4 M ............................ 45 3.3.6 6 M ............................ 49 3.3.7 7 M ............................ 49 3.4 Model Comparisons . 51 3.4.1 Models with Convective Overshooting . 55 3.5 Summary . 57 4 TP-AGB Stars of Low Metallicity 58 4.1 The Z = 0.008 Models – TP-AGB Stars in the LMC . 58 4.2 The Z = 0.004 Models – TP-AGB Stars in the SMC . 62 ii 4.3 The Carbon Star Luminosity Function . 65 4.3.1 LMC Models . 66 4.3.2 SMC models . 67 4.3.3 Population Synthesis . 67 4.4 Detailed Model Comparison . 72 4.4.1 Evolutionary Properties . 73 4.4.2 Focusing on a Pulse . 76 4.5 Summary . 82 5 Nucleosynthesis on the TP-AGB 83 5.1 Updating the Algorithms . 83 5.1.1 Charged Particle Reaction Rates . 86 5.1.2 Neutron Capture Rates . 86 5.2 Light Isotope Nucleosynthesis . 90 5.2.1 Nucleosynthesis During a Thermal Pulse . 90 5.2.2 Surface Composition Evolution . 91 5.3 The 13C Pocket: a Warning on Numerical Diffusion . 105 5.4 Summary . 108 6 Post-AGB Stars 110 6.1 The End of the TP-AGB . 110 6.2 Producing a Post-AGB Model . 111 6.3 Modelling a Late Thermal Pulse . 118 6.4 Summary . 121 7 Summary and Future Directions 122 7.1 Evolution . 122 7.2 Nucleosynthesis . 126 iii A Derivation of Gravothermal Specific Heat Capacity and Thermal Stability Criterion 137 A.1 The Gravothermal Specific Heat Capacity . 137 A.2 The Thermal Stability Criterion . 139 B Details of the Solar Metallicity Models 141 C Details of the LMC Metallicity Models 150 D Details of the SMC Metallicity Models 156 Bibliography 156 iv List of Figures 1.1 Hertzsprung-Russell diagram for a 1 M star of Z=0.008, showing its transition from the main sequence to the red giant branch. This model is evolved without mass loss. 4 1.2 Hertzsprung-Russell diagram for a 1 M star of Z=0.008, showing its transition from core helium burning to the AGB. 6 1.3 Interior structure of a typical AGB star. 7 1.4 The ubiquitous AGB TDUP figure . 11 2.1 Schematic depiction of the connections of the various subrou- tines in the stars code. 28 3.1 Evolution of the helium luminosity of the 5 M model. 36 3.2 Evolution of the core masses of the 5 M model. 37 3.3 Evolution of the CNO abundances of the 5 M model. 37 3.4 Evolution of the helium luminosity of the 1 M model. 39 3.5 Evolution of the core masses of the 1 M model. 40 3.6 Evolution of the helium luminosity of the 1.5 M model. 41 3.7 Evolution of the core masses of the 1.5 M model. 42 3.8 Evolution of the CNO abundances of the 1.5 M model. 42 3.9 Evolution of the helium luminosity of the 2 M model. 43 3.10 Evolution of the core masses of the 2 M model. 44 v 3.11 Evolution of the CNO abundances of the 2 M model. 44 3.12 Evolution of the helium luminosity of the 3 M model. 45 3.13 Evolution of the core masses of the 3 M model. 46 3.14 Evolution of the CNO abundances of the 3 M model. 46 3.15 Evolution of the helium luminosity of the 4 M model. 47 3.16 Evolution of the core masses of the 4 M model. 48 3.17 Evolution of the CNO abundances of the 4 M model. 48 3.18 Evolution of the helium luminosity of the 6 M model. 49 3.19 Evolution of the core masses of the 6 M model. 50 3.20 Evolution of the CNO abundances of the 6 M model. 50 3.21 Evolution of the helium luminosity of the 7 M model. 51 3.22 Evolution of the core masses of the 7 M model. 52 3.23 Evolution of the CNO abundances of the 7 M model. 52 4.1 Evolution of the core masses for the Z = 0.008 1 M model . 60 4.2 Evolution of the CNO abundances for the Z = 0.008 1 M model . 60 4.3 Evolution of the helium luminosity for the Z = 0.008 1.5 M model . 61 4.4 Evolution of the CNO abundances for the Z = 0.008 4 M model .
Load more

Recommended publications
  • Appendix: Spectroscopy of Variable Stars
    Appendix: Spectroscopy of Variable Stars As amateur astronomers gain ever-increasing access to professional tools, the science of spectroscopy of variable stars is now within reach of the experienced variable star observer. In this section we shall examine the basic tools used to perform spectroscopy and how to use the data collected in ways that augment our understanding of variable stars. Naturally, this section cannot cover every aspect of this vast subject, and we will concentrate just on the basics of this field so that the observer can come to grips with it. It will be noticed by experienced observers that variable stars often alter their spectral characteristics as they vary in light output. Cepheid variable stars can change from G types to F types during their periods of oscillation, and young variables can change from A to B types or vice versa. Spec­ troscopy enables observers to monitor these changes if their instrumentation is sensitive enough. However, this is not an easy field of study. It requires patience and dedication and access to resources that most amateurs do not possess. Nevertheless, it is an emerging field, and should the reader wish to get involved with this type of observation know that there are some excellent guides to variable star spectroscopy via the BAA and the AAVSO. Some of the workshops run by Robin Leadbeater of the BAA Variable Star section and others such as Christian Buil are a very good introduction to the field. © Springer Nature Switzerland AG 2018 M. Griffiths, Observer’s Guide to Variable Stars, The Patrick Moore 291 Practical Astronomy Series, https://doi.org/10.1007/978-3-030-00904-5 292 Appendix: Spectroscopy of Variable Stars Spectra, Spectroscopes and Image Acquisition What are spectra, and how are they observed? The spectra we see from stars is the result of the complete output in visible light of the star (in simple terms).
    [Show full text]
  • GEORGE HERBIG and Early Stellar Evolution
    GEORGE HERBIG and Early Stellar Evolution Bo Reipurth Institute for Astronomy Special Publications No. 1 George Herbig in 1960 —————————————————————– GEORGE HERBIG and Early Stellar Evolution —————————————————————– Bo Reipurth Institute for Astronomy University of Hawaii at Manoa 640 North Aohoku Place Hilo, HI 96720 USA . Dedicated to Hannelore Herbig c 2016 by Bo Reipurth Version 1.0 – April 19, 2016 Cover Image: The HH 24 complex in the Lynds 1630 cloud in Orion was discov- ered by Herbig and Kuhi in 1963. This near-infrared HST image shows several collimated Herbig-Haro jets emanating from an embedded multiple system of T Tauri stars. Courtesy Space Telescope Science Institute. This book can be referenced as follows: Reipurth, B. 2016, http://ifa.hawaii.edu/SP1 i FOREWORD I first learned about George Herbig’s work when I was a teenager. I grew up in Denmark in the 1950s, a time when Europe was healing the wounds after the ravages of the Second World War. Already at the age of 7 I had fallen in love with astronomy, but information was very hard to come by in those days, so I scraped together what I could, mainly relying on the local library. At some point I was introduced to the magazine Sky and Telescope, and soon invested my pocket money in a subscription. Every month I would sit at our dining room table with a dictionary and work my way through the latest issue. In one issue I read about Herbig-Haro objects, and I was completely mesmerized that these objects could be signposts of the formation of stars, and I dreamt about some day being able to contribute to this field of study.
    [Show full text]
  • Abstracts of Talks 1
    Abstracts of Talks 1 INVITED AND CONTRIBUTED TALKS (in order of presentation) Milky Way and Magellanic Cloud Surveys for Planetary Nebulae Quentin A. Parker, Macquarie University I will review current major progress in PN surveys in our own Galaxy and the Magellanic clouds whilst giving relevant historical context and background. The recent on-line availability of large-scale wide-field surveys of the Galaxy in several optical and near/mid-infrared passbands has provided unprecedented opportunities to refine selection techniques and eliminate contaminants. This has been coupled with surveys offering improved sensitivity and resolution, permitting more extreme ends of the PN luminosity function to be explored while probing hitherto underrepresented evolutionary states. Known PN in our Galaxy and LMC have been significantly increased over the last few years due primarily to the advent of narrow-band imaging in important nebula lines such as H-alpha, [OIII] and [SIII]. These PNe are generally of lower surface brightness, larger angular extent, in more obscured regions and in later stages of evolution than those in most previous surveys. A more representative PN population for in-depth study is now available, particularly in the LMC where the known distance adds considerable utility for derived PN parameters. Future prospects for Galactic and LMC PN research are briefly highlighted. Local Group Surveys for Planetary Nebulae Laura Magrini, INAF, Osservatorio Astrofisico di Arcetri The Local Group (LG) represents the best environment to study in detail the PN population in a large number of morphological types of galaxies. The closeness of the LG galaxies allows us to investigate the faintest side of the PN luminosity function and to detect PNe also in the less luminous galaxies, the dwarf galaxies, where a small number of them is expected.
    [Show full text]
  • Astronomical Coordinate Systems
    Appendix 1 Astronomical Coordinate Systems A basic requirement for studying the heavens is being able to determine where in the sky things are located. To specify sky positions, astronomers have developed several coordinate systems. Each sys- tem uses a coordinate grid projected on the celestial sphere, which is similar to the geographic coor- dinate system used on the surface of the Earth. The coordinate systems differ only in their choice of the fundamental plane, which divides the sky into two equal hemispheres along a great circle (the fundamental plane of the geographic system is the Earth’s equator). Each coordinate system is named for its choice of fundamental plane. The Equatorial Coordinate System The equatorial coordinate system is probably the most widely used celestial coordinate system. It is also the most closely related to the geographic coordinate system because they use the same funda- mental plane and poles. The projection of the Earth’s equator onto the celestial sphere is called the celestial equator. Similarly, projecting the geographic poles onto the celestial sphere defines the north and south celestial poles. However, there is an important difference between the equatorial and geographic coordinate sys- tems: the geographic system is fixed to the Earth and rotates as the Earth does. The Equatorial system is fixed to the stars, so it appears to rotate across the sky with the stars, but it’s really the Earth rotating under the fixed sky. The latitudinal (latitude-like) angle of the equatorial system is called declination (Dec. for short). It measures the angle of an object above or below the celestial equator.
    [Show full text]
  • Precision Diagnostics of Pulsation and Evolution in Helium-Rich Low-Mass Stars
    Precision Diagnostics of Pulsation and Evolution in Helium-Rich Low-Mass Stars A dissertation submitted to the University of Dublin for the degree of Doctor of Philosophy Pamela Martin, B.A. (Mod). Armagh Observatory and Planetarium & Trinity College Dublin 2019 School of Physics University of Dublin Trinity College ii Declaration I declare that this thesis has not been submitted as an exercise for a degree at this or any other university and it is entirely my own work. I agree to deposit this thesis in the University's open access institutional repository or allow the Library to do so on my behalf, subject to Irish Copyright Legislation and Trinity College Library conditions of use and acknowledgement. Name: Pamela Martin Signature: ........................................ Date: .......................... Abstract In this thesis we discuss many types of low mass stars linked by their un- usually low hydrogen atmospheric abundance, usually completely replaced with helium. We begin with the hot subdwarfs; subdwarf O and B (sdB, sdO) stars are low-mass core helium burning stars with extremely low-mass hydrogen envelopes. Their atmospheres are generally helium deficient; how- ever a minority have extremely helium-rich surfaces. An additional fraction have an intermediate surface-helium abundance, occasionally accompanied by peculiar abundances of other elements. LS IV−14◦116 is a non-radially pulsating slowly-rotating chemically-peculiar helium-rich sdB with a 4 dex surface excess of zirconium, yttrium, and strontium. The pulsations are un- expected and unexplained, as the star is 6 000K hotter than the blue edge of the hot subdwarf g-mode instability strip. The presence of pulsations offers a rare opportunity to study the structure of the photosphere.
    [Show full text]
  • Pg Sagittae, a Test Op the Theory Op Evolution Op Double Shell Source Stars
    PG SAGITTAE, A TEST OP THE THEORY OP EVOLUTION OP DOUBLE SHELL SOURCE STARS Yu. A# Padeyev Astronomical Council USSR Academy of Sciences PG Sge is a unique stellar object possessing a number of unusual properties which are as follows: (1) PG Sge is a core of a planetary nebula, (2) at least since 1894 this star has crossed the HR diagram from the left to the right, (3) the atmosphere of PG Sge was enriched in s-elements, (4) PG Sge is a pulsating variable the period of which progressively Increases from 15 days in 1962 to 110 days in 1980. As it was primarily supposed by Paczynski (1971) PG Sge mores in the HR diagram along the horisontal loop due to a helium shell flash in its interior. This hypothesis provides not only the explanation of enriched surface abundances of s-elements but allows also to estimate both the distance and the age of the planetary nebula surrounding PG Sge* According to Plannery and Herbig (1973) the expansion velocity and the angular radius of the planetary nebula are 34 km/a and 18 arc sec, respectively* Thus, the age of the planetary nebula r is related to the distance d by log r (yr) ■ 0.400 + log d (pc) (1) Supposing that the planetary nebula was formed at the pre­ ceding helium f^ash, the interflash period - core mass relation (Paczynski, 1975) and the core mass - luminosity relation (Paczynski. 1970) can be used for obtaining another relation between the age of the planetary nebula and its distance: log r - 5.201 - 4.79 -10~8 d2.
    [Show full text]
  • Stellar Archaeology: the Evolving Spectrum of FG Sagittae
    A&A 459, 885–899 (2006) Astronomy DOI: 10.1051/0004-6361:20047075 & c ESO 2006 Astrophysics Stellar archaeology: the evolving spectrum of FG Sagittae C. S. Jeffery1 and D. Schönberner2 1 Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland e-mail: [email protected] 2 Astrophysikalisches Institut, Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany Received 14 January 2004 / Accepted 21 August 2006 ABSTRACT Over an interval of 120 years, the extraordinary object FG Sge has been transformed from a hot post-AGB star to a very luminous cool supergiant. Theoretically, this evolution has been associated with the reignition of a helium-shell during the post-AGB stage. A series of studies of the chemical composition of the photosphere have suggested that this evolution has been associated with a dramatic increase of approximately 3 dex in the abundances of s-process elements between about 1960 and 1995. The problem with this apparent change is that it occurred at a time when the surface convection zone, which is governed by the star’s effective temperature, could not have developed sufficiently to dredge processed material from the stellar interior to the surface. We have reviewed the chemical evolution of FG Sge by means of modelling the time-varying spectrum under a range of assumptions. By comparing these models with published observational data, a self-consistent picture has emerged. In particular we find that surface hydrogen has been depleted during the interval in question. In contrast, the s-process abundances have generally maintained a steady enhancement of around 1−2 dex, although some modest changes may have occurred since 1950.
    [Show full text]
  • The Asymptotic Giant Branch and Eventually Be- Come Planetary Nebulae and White Dwarfs
    The Early Asymptotic Giant Branch (E-AGB) • Because of mass loss during their evolution, stars with initial mass M < 8M¯ will end up with degenerate carbon-oxygen cores that are under the Chandrasekhar mass limit. These stars will evolve up the asymptotic giant branch and eventually be- come planetary nebulae and white dwarfs. More massive stars will undergo heavy element nucleosynthesis and a different evo- lutionary track. • When a star begins ascending the asymptotic giant branch, the luminosity of the star will again become a function solely of the mass of the helium core. Stars with high initial masses will have higher mass cores and, consequently, higher helium shell luminosities. Similarly, since the luminosity of the helium shell drives envelope expansion, higher (core) mass stars will evolve to larger radii. • As was the case for giant branch stars, the envelope expansion of asymptotic giant branch stars causes the opacity in the enve- lope to increase. This drives envelope convection. In stars with > initial masses M ∼ 3M¯, the convective envelope reaches all the way down to the dormant hydrogen burning shell. Products of hydrogen burning are then convected to the surface, enhancing the abundance of 4He, 14N and 13C at the expense of 12C and 16O. This is the second dredge-up phase; it only occurs in intermediate mass stars. In lower (initial) mass stars, where the shell luminosity is less, the convective envelope stops short of the hydrogen discontinuity, hence this second dredge-up does not occur. • The change in surface abundance for stars undergoing the sec- ond dredge-up depends on the initial mass of the star.
    [Show full text]
  • Astronomy 1973-2000 Author Index
    Astronomy magazine author index 1973-2000 Challenging Simulation Program, A, 5/88:79, 81 A Baliunas, Sallie Unfolding Mysteries of Stellar Cycles, 5/92:42–47 Abell, George O. Baneth Allen, Joseph Beyond the Milky Way, 1/75:6–24 Compact Disc Bound for Mars, 11/93:26 Achenbach, Joel Satellite Finds New Radiation Belt, 11/93:26 Captured by Aliens, 7/00:42–47 Barclay, Jim Adams, Amy Under the Southern Sky, 10/94:73–77 Triumph of Hipparcos, The, 12/97:60–63 Barger, M. Susan Adams, Fred C. Moon on a Silver Plate, The, 10/87:98–103 Embracing the End, 10/00:48–53 Barnes-Svarney, Patricia Ainsworth, Diane Chronology of Planetary Bombardments, 7/88:20–28 Mars Observer: Return to the Red Planet, 9/92:28–37 Frozen Assets, 10/97:46–47 Akins, Val Bartusiak, Marcia Successful Schmidt Camera Photography, 12/84:75–77 Astronomy Careers Beckon, 11/00:50–55 Albin, Edward F. Beast in the Core, A, 7/98:48–53 Observing the New Mars, 11/92:74–79 Catch Gravity Wave, 10/00:54–59 Allen, David Cosmic Jekyll & Hyde, 5/98:50–53 Huntsman Nebula, The, 9/92:38–39 Gravity's Rainbow, 8/97:44–49 Allen, Joseph Baneth New Dark Age of Astronomy, The, 10/96:36–39 Asteroid Narrowly Misses Earth, 5/91:22 Outsmarting the Early Universe, 10/98:54–59 Did Viking See A Martian Landslide?, 11/92:22, 24 Remarkable Odyssey of Jane Luu, The, 2/96:46–51 Radio Images Reveal Hidden Arcs in Orion, 8/91:22 Underground Astronomer, 1/00:64–67 Anderson, Jay What Makes Galaxies Change?, 1/97:36–43 Eclipse Prospects for the 1990s, 2/89:71–76 Baumgardt, Jim Return to Darkness, 11/93:88–93 Astrophotography without a Telescope, 1/87:46–51 Sunblock, 2/94:74–78 Simple and Inexpensive Tricolor Photography, 11/83:51–54 Andreadis, Athena Baum, Richard Good Planets Are Hard to Find, 1/99:64–69 Neptune's Discovery 150 Years Later, 9/96:43–49 Annett, Clarence H.
    [Show full text]
  • The Spectrum of Fg Sagittae After Photometric Recovery in 2000
    Baltic Astronomy, vol. 10, 393-401, 2001. THE SPECTRUM OF FG SAGITTAE AFTER PHOTOMETRIC RECOVERY IN 2000 Tonu Kipper1 and Valentina G. Klochkova2 1 Tartu Observatory, Toravere, 61602, Estonia 2 Special Astrophysical Observatory, Nizhnij Arkhyz, 357147, Karachaevo-Cherkessia, Russian Federation Received November 15, 2000. Abstract. The high resolution spectra of FG Sge obtained in 2000, after the stars photometric recovery from a deep brightness drop, are analysed. The elemental abundances are derived using the spectral synthesis method. The results show that the abundances are close to the ones before the fading which means that the increase in carbon and 5 — process elements abundances has levelled out. Key words: stars: atmospheres, late-type, individual: FG Sge 1. INTRODUCTION The remarkable variable star FG Sge was photometrically very active in recent years. Starting in 1992, it shows R CrB-like bright- ness drops. At the same time the very broad blue-shifted absorption components of the Nal D doublet profiles indicate intensive mass loss (Kipper et al. 1995). These phenomena have been suggested to follow the last helium flash in the shell of the star. Also recorded are the variations of the C2 band strengths and the appearance of emission lines and the C2 emission bands during the light minima (Smith et al. 1996, Kipper & Klochkova 1999). The story of FG Sge until 1995 was presented by Kipper (1996). The latest thorough re- views of FG Sge studies were given by Gonzalez et al. (1998) and by Jurcsik & Montesinos (1999), where the observations until the end of 1996 were discussed. 394 T.
    [Show full text]
  • Astronomy 1973-2000 Title Index
    Astronomy magazine title index 1973-2000 Afocal and Projection Astrophotography, 8/81:57–59 # Afro-American Skylore Studied, 1/79:61 Against All Odds: Matter and Evolution in the Universe, 100 Years on Mars, 6/94:28–39, 28–39 9/84:67–70 10-Meter Keck Telescope to Gain Twin, 8/91:18, 20, 22 Age of Nearby Stars, The, 7/75:22–27, 22–27 11-Mintute Binary?, An, 1/87:85–86 Age of the Universe, The, 7/81:66–71 12 1/2 -inch Ritchey-Chretien, A, 11/82:55–57 Age Paradox, The, 6/93:38–43 12.5 Inch Portaball, The, 3/95:80–85, 80–85 Aid to Long Exposure Astrophotography, An, 10/73:35–39, 35–39 13th Jovian Moon Discovered, 11/74:55 Aiming at Neptune, 11/87:6–17 14th Jovian Moon, 1/76:60 Airborne Assault on Comet Halley, 3/86:90–95 15 Years of Space, 1/77:55 Alan B. Shepard (1923-1998), 11/98:32, 34 169th Meeting of the American Astronomical Society, The, Alcock's Nova Resurges, 2/77:59 4/87:76 ALCON Lands in Rockford, 1/97:32, 34 17th-Century Nova Indicates Novae are More Numerous then Aldebaran's Girth, 7/79:60 Estimated, 5/86:72 Alexis Lives!, 3/94:24 1976 AA: Discovery of a Minor Planet, 6/76:12–13, 12–13, 12–13, Alien Skies, 4/82:90–95 12–13 Alignment By Laser Light, 4/95:82–83, 82–83 1989 Ends With a Leap Second, 12/89:12 A List, The, 2/98:34 1990 Radio-Video Star Party, The, 4/91:26 All About Telesto, 7/84:62 1 Billion Degree Plasma Discovered by Voyager 2, 1/82:64–65 All Eyes on the Comet Crash, 6/94:40–45, 40–45 1st Extragalactic Pulsar Discovered, 2/76:63 All in the Family, 2/93:36–41 1st Shuttle Payload to Study Resources and Environment,
    [Show full text]
  • 168, June 2016
    British Astronomical Association VARIABLE STAR SECTION CIRCULAR No 168, June 2016 Contents If you happen to be passing my door - D Buczynski ............. inside front cover From the Director - R Pickard ............................................................................ 3 The IAU Transient Name Server and Spectroscopic Confirmation of Supernova Candidate AT2016bme - R Leadbeater ................. 4 SU Lyncis – A New Symbiotic Variable - D Boyd........................................... 7 The Variable Star Section Meeting at Northampton 19th March 2016 - T Markham .......................................... 9 Eclipsing Binary News - D Loughney ............................................................. 15 IBVS 6145 – 6175 - J Simpson ....................................................................... 16 Binocular Programme - S Albrighton ................................................................ 17 Eclipsing Binary Predictions – Where to Find Them - D. Loughney .............. 18 Charges for Section Publications .............................................. inside back cover Guidelines for Contributing to the Circular .............................. inside back cover ISSN 0267-9272 Office: Burlington House, Piccadilly, London, W1J 0DU Photograph kindly taken by Liz Buczynski “IF YOU HAPPEN TO BE PASSING MY DOOR!” DENIS BUCZYNSKI Occasionally BAA members on holiday in Scotland, who are perhaps driving to Ork- ney, pass (on the A9) within 10 miles of my home and observatory at Portmahomack on the Tarbatness peninsula; sometimes they call in to see me. I would like to extend an invite to any BAA or VSS member who would like to visit to do so. If you know ahead of time that you will be visiting the area, please contact me by e-mail < [email protected] >, or if it is at short notice, when you realise you are passing close to Portmahomack, it would be quicker and easier to contact me by phone: Tel: 01862 871187. Both my e-mail address and my telephone number are now on the back cover of the Circular.
    [Show full text]