DOCSLIB.ORG

Research Programme: Helium-Rich Subdwarfs and Connections in Stellar Evolution Summary. the Chemical Structure of Early-Type

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Research Programme: Helium-Rich Subdwarfs and Connections in Stellar Evolution Summary. the Chemical Structure of Early-Type Research Programme: Helium-rich subdwarfs and connections in stellar evolution Summary. The chemical structure of early-type stars is susceptible to atomic diffusion driven by radiative levitation and gravitational settling on timescales comparable with stellar evolution. Such diffusion can lead to chemical stratification of the stellar atmosphere and envelope, to the formation of extremely chemically peculiar stars and to the existence of undiscovered classes of pulsating stars. This is particularly true for evolved stars and especially hot subdwarfs and related objects. Most remarkable are the heavy-metal subdwarfs, which present extreme surface chemistries, undetectable surface rotation, pulsations indicative of a C+O dominated interior, and galactic halo-like orbits. Challenges lie in identifying and characterising new classes of chemically peculiar and/or pulsating stars, in creating self-consistent models of the stellar atmosphere, envelope and pulsations with appropriate atomic data, and, most significantly, in placing these stars in the broader context of their origin, evolution and their relationship to other classes of evolved star. The goals of this project and the associated work packages (WP) are to: i) better characterise the hot helium-rich (He-rich) subdwarfs and related objects (WP1); ii) build new models for their atmospheres and envelopes including self-consistent atomic diffusion theory and new atomic data (WP2); iii) explain the distribution of chemical peculiarities and how these align with new classes of pulsating star (e.g. zirconium-rich pulsators) (WP2+3); iv) identify the origin of the most exotic classes of He-rich subdwarf and their connections with other evolved stars (WP3); and v) develop new models to better exploit information from pulsating subdwarfs (WP4). Background Early calculations of stellar opacities demonstrated the possible existence of a high temperature bump (Carson+ 1981). Whilst premature (Carson+ 1984), major efforts to recalculate stellar opacities (OP 1987, OPAL 1992) revealed a significant contribution from iron-group elements at temperatures of ≈ 2 × 105 K. This ‘iron bump’ provided the long- searched for explanation of pulsation observed in many B stars, (β Cep: Moskalik & Dziembowski 1992, V652 Her: Saio 1993) and led to the prediction of pulsation in hot subdwarfs (Charpinet+ 1997). The many classes of pulsating early type variable (Fig. 1) include p- and g-mode pulsations in subdwarf B stars (EC14026: Kilkenny+ 1997, PG1716: Green+ 2003), low-amplitude pulsations in low-mass pre-white dwarfs (WDs) (EL CVn: Maxted+ 2014), He-rich subdwarfs (V366Aqr: Ahmad & Jeffery 2005, Green+ 2011), and large amplitude pulsations in faint blue stars (BLAPs: Pietrukowicz+ 2017, Kupfer+ 2019). In all cases, significant features in opacity are responsible for driving the pulsations (Jeffery & Saio 2006, 2013, 2016, Saio & Jeffery 2019, Byrne & Jeffery 2020). For low-mass hot stars, the opacity bump from iron and nickel (in particular) provides the driving mechanism, with carbon and oxygen opacity driving pulsations in the hottest stars. In most cases the opacity bump is only effective as a pulsation driver if coupled with either depletion of background opacity from hydrogen or high concentrations of specific elements. Radiative opacities in faint blue stars also mediate gravitational settling and radiative levitation, with increased opacity due to ionisation providing a nett upward force on specific ions. The maximum value of this force occurs at the same temperature as the peak in 1 Figure 1: Hertzsprung–Russell diagram showing locations of principal classes of pulsating star. Normal stellar evolution from the main-sequence is illustrated, tracks labelled by mass. Classes are coloured roughly by spectral type. Shadings represent opacity-driven p modes (\), g modes (/) and strange modes (|) and acoustically driven modes (−) [after J. Christensen- Dalsgard]. opacity and, if undisturbed, leads to high concentrations of these elements, effectively amplifying the local opacity. Conversely, low specific opacities lead to low concentrations. These phenomena are enhanced at high surface gravities, i.e. in hot WDs and subdwarfs. The latter dominate the ultraviolet component of evolved stellar systems including globular clusters and giant elliptical galaxies (Brown+ 2003). The largest class of hot subdwarf, the subluminous B (sdB) stars, are conventionally core-burning helium stars of ≈ 0.5 M⊙which have helium- poor atmospheres; settling dominates, but the surface helium fraction increases with Teff(Heber , Edelmann+ 2003). Meanwhile, multiple classes of helium- enriched hot subdwarf (Drilling+ 2013) merit special attention, despite the extreme rarity of 2 Figure2: The distribution of heavy metal (filled symbols; Zr:maroon, Pb:blue and yellow), metal- normal(open symbols), He-rich and normal hot subdwarfs with effective temperature (Teff), surface gravity (g: left) and surface He/H ratio (y: right) some species. In about 10% of hot subdwarfs, hydrogen is so deficient there is insufficient to conceal the helium; an origin that destroys hydrogen seems probable (Zhang & Jeffery 2012). In the gap between helium- poor and hydrogen-poor subdwarfs (Fig. 2) lies a sparse group of intermediate helium subdwarfs (Naslim+ 2012). This group consistently displays remarkable properties. Their surfaces are super-abundant in trans-iron elements and form two groups, the cooler zirconium-rich and the hotter lead-rich (heavy-metal subdwarfs; Naslim+ 2011, Naslim+ 2013, Jeffery+ 2017a, Dorsch+ 2019, Latour+ 2019, Jeffery & Miszalski 2019, Naslim+ 2020). All show very sharp absorption lines indicative of low surface rotation (ibid.). The zirconium stars pulsate in g-modes driven by carbon and oxygen opacities at ≈ 106 K (Saio & Jeffery 2019). The majority are in high-energy galactic (halo?) orbits (Martin 2018). These remarkable stars form the primary focus of this proposal; why are their surfaces hydrogen/helium poor? why are they chemically peculiar? how did they form? what is their internal structure? do they have C+O-rich cores? what gave them their high velocities? why do they lie at the upper Teff boundary of normal sdB stars? how are they connected with other classes of hot subdwarfs and hydrogen-deficient stars? WP1. The SALT survey of chemically peculiar subdwarfs: PI Year 1 - 2. The PI is leading a spectroscopic survey of all southern He-rich hot ‘subdwarfs’ using SALT with resolution and S/N sufficient to measure atmospheric properties (mV ≤ 16) and detailed surface composition (mV ≤ 14.5). The survey has discovered several new extreme helium stars, a heavy-metal subdwarf and other stars of interest (Fig. 3: Jeffery 2017, Jeffery+ 2017b, Jeffery & Miszalski 2019). This WP covers classification, parameterization and a spectroscopic atlas of the entire sample (≈ 200 stars), together with follow-up analyses of interesting objects and will be carried out by the PI and an STFC-PhD student (Ted Snowdon). The PI is also a LAMOST consortium member and will extend the survey to the northern hemisphere using data already available. WP2. Stratified model atmospheres for heavy-metal subdwarfs: PDRA Year 1 – 2. 3 Current abundance analyses of heavy-metal subdwarfs indicate surface abundances of trans-iron elements which are ≈ 104 times solar. Surface enrichment of material produced by the s-process is possible but unlikely; these are not post-AGB stars. Alternatively, the enriched material forms a thin layer supported by radiative levitation. If centered at the line- forming depth in the photosphere, Figure 3: Surface properties of selected SALT an abundance measurement would subdwarfs (red), extreme helium stars (black reflect the abundance in that layer, squares), extreme helium subdwarfs (black diamonds) but not the mean abundance in the and intermediate helium subdwarfs (violet photosphere. diamonds). The Eddington limit, LM contours (solar Two tests will be made using model units), zero-age helium main-sequence, a He+He WD atmospheres with a non-uniform post-merger track (Zhang & Jeffery 2012) (maroon), chemical distribution; i) the and a ’late hot flasher’ track (Miller Bertolami et al. distribution will be assigned 2008) (orange) are also shown. parametrically assuming discontinuities above and/or below the enriched layer. Theoretical line profiles will be compared with observed profiles to established the allowed range at which these discontinuities might occur. ii) our existing model atmosphere code (sterne: Behara+ 2006) includes provision for self-consistent radiative levitation and gravitational settling (Behara 2007). We will upgrade this code to incorporate additional opacities for trans-iron species (Fernandez-Menchero+ 2020, in prep) and hence determine whether radiative levitation can produce the observed concentrations. A key test will be to demonstrate how effective temperature affects different species; the peak concentration temperatures or Pb3+ and Zr3+ should reflect Pb- rich subdwarfs occurring at higher Teff than Zr-rich subdwarfs (Fig. 2). Data for these tests exist in the form of high signal-to-noise échelle spectra of several Zr- and Pb-rich subdwarfs. Information about stratification of less exotic elements will be equally important. Atomic data are being generated through a collaboration with Queens University Belfast. Fine analyses will be supplemented by analyses of spectral energy distributions and Gaia distances to determine radii and masses more precisely than hitherto, and to confront
Load more

Recommended publications
  • Evolution and Understanding of the D-Block Elements in the Periodic Table Cite This: Dalton Trans., 2019, 48, 9408 Edwin C
    Dalton Transactions View Article Online PERSPECTIVE View Journal | View Issue Evolution and understanding of the d-block elements in the periodic table Cite this: Dalton Trans., 2019, 48, 9408 Edwin C. Constable Received 20th February 2019, The d-block elements have played an essential role in the development of our present understanding of Accepted 6th March 2019 chemistry and in the evolution of the periodic table. On the occasion of the sesquicentenniel of the dis- DOI: 10.1039/c9dt00765b covery of the periodic table by Mendeleev, it is appropriate to look at how these metals have influenced rsc.li/dalton our understanding of periodicity and the relationships between elements. Introduction and periodic tables concerning objects as diverse as fruit, veg- etables, beer, cartoon characters, and superheroes abound in In the year 2019 we celebrate the sesquicentennial of the publi- our connected world.7 Creative Commons Attribution-NonCommercial 3.0 Unported Licence. cation of the first modern form of the periodic table by In the commonly encountered medium or long forms of Mendeleev (alternatively transliterated as Mendelejew, the periodic table, the central portion is occupied by the Mendelejeff, Mendeléeff, and Mendeléyev from the Cyrillic d-block elements, commonly known as the transition elements ).1 The periodic table lies at the core of our under- or transition metals. These elements have played a critical rôle standing of the properties of, and the relationships between, in our understanding of modern chemistry and have proved to the 118 elements currently known (Fig. 1).2 A chemist can look be the touchstones for many theories of valence and bonding.
    [Show full text]
  • In-System'' Fission-Events: an Insight Into Puzzles of Exoplanets and Stars?
    universe Review “In-System” Fission-Events: An Insight into Puzzles of Exoplanets and Stars? Elizabeth P. Tito 1,* and Vadim I. Pavlov 2,* 1 Scientific Advisory Group, Pasadena, CA 91125, USA 2 Faculté des Sciences et Technologies, Université de Lille, F-59000 Lille, France * Correspondence: [email protected] (E.P.T.); [email protected] (V.I.P.) Abstract: In expansion of our recent proposal that the solar system’s evolution occurred in two stages—during the first stage, the gaseous giants formed (via disk instability), and, during the second stage (caused by an encounter with a particular stellar-object leading to “in-system” fission- driven nucleogenesis), the terrestrial planets formed (via accretion)—we emphasize here that the mechanism of formation of such stellar-objects is generally universal and therefore encounters of such objects with stellar-systems may have occurred elsewhere across galaxies. If so, their aftereffects may perhaps be observed as puzzling features in the spectra of individual stars (such as idiosyncratic chemical enrichments) and/or in the structures of exoplanetary systems (such as unusually high planet densities or short orbital periods). This paper reviews and reinterprets astronomical data within the “fission-events framework”. Classification of stellar systems as “pristine” or “impacted” is offered. Keywords: exoplanets; stellar chemical compositions; nuclear fission; origin and evolution Citation: Tito, E.P.; Pavlov, V.I. “In-System” Fission-Events: An 1. Introduction Insight into Puzzles of Exoplanets As facilities and techniques for astronomical observations and analyses continue to and Stars?. Universe 2021, 7, 118. expand and gain in resolution power, their results provide increasingly detailed information https://doi.org/10.3390/universe about stellar systems, in particular, about the chemical compositions of stellar atmospheres 7050118 and structures of exoplanets.
    [Show full text]
  • United States Patent (19) 11 4,412,981 Kubicek 45) Nov
    United States Patent (19) 11 4,412,981 Kubicek 45) Nov. 1, 1983 54 CONVERSION OF HYDROGEN SULFIDE TO 3,103,411 9/1963 Fuchs .............................. 423/224 X SULFUR BY DIRECT OXDATION 3,516,793 6/1970 Renault.... ... 42.3/573 3,914,309 10/1975 Beazley ............ ... 42.3/573 (75) Inventor: Donald H. Kubicek, Bartlesville, 4,313,916 2/1982 Jones et al. ......................... 423/226 Okla. FOREIGN PATENT DOCUMENTS 73) Assignee: Phillips Petroleum Company, Bartlesville, Okla. 1080530 7/1957 Fed. Rep. of Germany ...... 423/573 1492797 8/1967 France ................................ 423/573 597655 5/1945 United Kingdom ... ... 42.3/571 21 Appl. No.: 302,942 84.1610 7/1960 United Kingdom.... ... 42.3/573 (22 Filed: Sep. 16, 1981 1182255 2/1970 United Kingdom................ 423/573 51) Int. Cl........................ C01B 17/04; B01D 53/34 Primary Examiner-Earl C. Thomas 52 U.S.C. ................................ 423/573 R; 423/224; 57) ABSTRACT 423/226; 210/758; 208/235 58) Field of Search ............... 423/224, 226,571, 573; In a process wherein hydrogen sulfide is converted to 208/235; 55/73; 210/758, 763 elemental sulfur in the presence of oxygen, an improve ment is made by employing an alcoholic solution of an 56 References Cited alkali metal hydroxide, free of iron-group salts or other U.S. PATENT DOCUMENTS heterogeneous catalysts. High yields of pure sulfur are 2,556,836 6/1951 Browder et al. obtained from such reactions begun at room tempera 2,600,328 6/1952 Riesenfeld et al. ............. 423/226X ture, without a requirement for heterogeneous catalysts 2,972,522 2/1961 Urban .
    [Show full text]
  • On a Group-Theoretical Approach to the Periodic Table of Chemical Elements Maurice Kibler
    On a group-theoretical approach to the periodic table of chemical elements Maurice Kibler To cite this version: Maurice Kibler. On a group-theoretical approach to the periodic table of chemical elements. Jun 2004, Prague. hal-00002554 HAL Id: hal-00002554 https://hal.archives-ouvertes.fr/hal-00002554 Submitted on 16 Aug 2004 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. On a group-theoretical approach to the periodic table of chemical elements Maurice R. Kibler Institut de Physique Nucl´eaire de Lyon IN2P3-CNRS et Universit´eClaude Bernard 43 Bd du 11 Novembre 1918, F-69622 Villeurbanne Cedex, France This paper is concerned with the application of the group SO(4, 2)⊗SU(2) to the periodic table of chemical elements. It is shown how the Madelung rule of the atomic shell model can be used for setting up a periodic table that can be further rationalized via the group SO(4, 2)⊗SU(2) and some of its subgroups. Qualitative results are obtained from the table and the general lines of a programme for a quantitative approach to the properties of chemical elements are developed on the basis of the group SO(4, 2)⊗SU(2).
    [Show full text]
  • Program Description the Diversity of Transition Metals Provides Versatility in Their Practical Applications
    Periodic Table of the Elements Transition Metals III Teacher’s Guide oneone oee Grade Level: 9–12 Curriculum Focus: Physical Science Lesson Duration: Two class periods Program Description The diversity of transition metals provides versatility in their practical applications. Vanadium provides strength and flexibility on a major U.S. aircraft carrier. Zirconium’s unique properties make it ideal for use in nuclear reactors. And mercury maintains happy mouths through its use in dental fillings. Lesson Summary Students identify the transition elements on the periodic table of the elements and discuss their key characteristics before conducting an experiment that shows what happens when iron reacts with oxygen in air and water: An exothermic reaction takes place, and heat is released. Salt acting as a catalyst helps the reaction take place faster, and vermiculite helps hold in the heat. Onscreen Questions Part 1, “Exploring Transition Metals,” “Vanadium: Strengthening Steel,” “Zirconium: Nuclear Necessity,” “and “Mercury: Weather Wizard” • What properties do the transition metals share? • How does a nuclear reactor generate electricity? Part 2, “Extreme Machine: Oil Rig” • How does oil form? • What makes the Erik Raude different from a traditional oil rig? Lesson Plan Student Objectives • Identify the transition metals on the periodic table of the elements and describe their characteristics. • Predict what will happen when one transition metal is mixed with water and sealed in a bag. Periodic Table of the Elements Transition Metals III Teacher’s Guide 2 • Describe the results of the investigation and explain how it illustrated a property of one of the transition metals. Materials • Transition Metals II program • Newsprint and markers • Copy of the periodic table of the elements For each group • 1 tablespoon iron filings • ¼ teaspoon salt • 1 tablespoon vermiculite (available in garden shops) • 1 teaspoon tap water • 1 resealable plastic bag • Measuring spoons Procedures 1.
    [Show full text]
  • Direct & Pulse Current Electrodeposition of Iron Group
    Technical Article Direct & Pulse Current Electrodeposition Of Iron Group Thin Film Alloys Containing Vanadium by M. Schwartz, C. Arcos & K. Nobe* Direct current (DC) and pulse current (PC) electrode- tion (Bs), low coercivity (Hc), near zero magnetostriction position of binary and ternary alloys of the iron group (λ) and high permeability (µ).3 (IG) metals and vanadium are discussed. 90 Co/10 Fe Electrodeposited Permalloy (80 Ni/20 Fe) fi lms have alloy compositions with substitutional additions of such desirable magnetic properties and have been used desirable small amounts of V (~2%) were obtained; exclusively as pole material in thin fi lm heads for digital Co-Ni-V and Ni-Fe-V alloys were also deposited. recording.4 However, projections of higher storage density The effects of complexer, pH and current density on and output performance for recording applications show deposit composition and cathode current effi ciency that soft magnetic materials superior to Permalloy are (CCE) are discussed and compared to deposition of required.2 Thus, considerable effort has been directed to binary alloys of the iron group only. Impedance mea- the development of materials similar to Permalloy but with surements indicate greater corrosion resistance for higher magnetic saturation, higher permeability and higher ternary Co-Fe-V alloys than for binary Co-Fe alloys. resistivity.5,6 Crude magnetic measurements show approximately Since the discovery of the giant magnetoresistance two times greater “relative magnetic moments” for (GMR) effect in 1988, i.e., the change in electrical resis- Co-Fe-V deposits than for deposits from typical Ni-Fe tance in response to an applied magnetic fi eld, it has (Permalloy) solutions.
    [Show full text]
  • The Periodic System of Chemical Elements: Old and New Developments
    ^o-f^oiî-irt, Lycen 87*i^ bept. lyfl; THE PERIODIC SYSTEM OF CHEMICAL ELEMENTS: OLD AND NEW DEVELOPMENTS fl. KIBl.EH Institut de Physique Nucléaire (et IN2P3)» Université Lyon-1. 43. Bd du 11 Novembre 1918. 69622 Villeurbanne Cedex (France) (Invited conference to the: "XVII CONGRESO DE BUI Ml COS TEORICOS DE EXPRES I ON LATIN A". Pemscola. Spain. September 20-25. 1987. ) Article accepted for publication in J. Mol. Struct. (THEOCHEM). THE PERIODIC SYSTEM OF CHEMICAL ELEMENTS: OLD AND NEW DEVELOPMENTS M. K1BLER Institut de Physique Nucléaire (et IN2P3). Université Lyon-1. 43. Bd du 11 Novembre 1918. 69622 Villeurbanne Cedex (France) SUMMARY Some historical facts about the construction of a periodic system of chemical elements are reviewed. The Madelung rule is used to generate an unusual format for the periodic table. Following the uork of Byakov< Kulakov. Rumer and Fet. such a format is further refined on the basis of a chain of groups starting with SU(2)xS0(4.2). HISTORICAL FACETS The list of chemical elements has not stopped to grow during the last two centuries. In a schematic way. ue have the following guiding-marks (where [xxx. xxx. xxx ] stands for [year. number of elements. representative person(a) ]): (1789. 23. Lavoisier!. C1815. 30. FroutJ. C1818. 40. Berzeliusl. C1828. 49, Berzeliusl. C1849, 61. Gmelin]. I 1865. 63. Meyer and Mendeleev]. C1940. 86. - 3, C1973. 105. - ] and C1987. 109. - 3. Among the first attempts to classify chemical elements. we may mention the Doebereiner triads, the Pettenkofer groupings. the Chancourtois spiral. the Newlands octaves and the tableB by Olding and Lothar Meyer (cf.
    [Show full text]
  • Iron-Group Opacities in the Envelopes of Massive Stars
    Precision Asteroseismology Proceedings IAU Symposium No. 301, 2013 c International Astronomical Union 2014 J. A. Guzik, W. J. Chaplin, G. Handler & A. Pigulski, eds. doi:10.1017/S1743921313014373 Iron-group opacities in the envelopes of massive stars Ma¨elle Le Pennec and Sylvaine Turck-Chi`eze CEA/DSM/IRFU/SAp, CE Saclay, 91191 Gif-sur-Yvette, France email: [email protected]; [email protected] Abstract. β Cephei and SPB stars are pulsating stars for which the excitation of modes by the κ mechanism, due to the iron-group opacity peak, seems puzzling. We have first investigated the origins of the differences noticed between OP and OPAL iron and nickel opacity calculations (up to a factor 2), a fact which complicates the interpretation. To accomplish this task, new well- qualified calculations (SCO-RCG, HULLAC and ATOMIC) have been performed and compared to values of these tables, and most of the differences are now well understood. Next, we have exploited a dedicated experiment on chromium, iron and nickel, conducted at the LULI 2000 facilities. We found that, in the case of iron, detailed calculations (OP, ATOMIC and HULLAC) show good agreement, contrary to all of the non-detailed calculations. However, in the case of nickel, OP calculations show large discrepancies with the experiments but also with other codes. Thus, the opacity tables need to be revised in the thermodynamical conditions corresponding to the peak of the iron group. Consequently we study the evolution of this iron peak with changes in stellar mass, age, and metallicity to determine the relevant region where these tables should be revised.
    [Show full text]
  • Alkali Or Alkaline -Earth Metals
    28.05 28.05 - Alkali or alkaline-earth metals; rare-earth metals, scandium and yttrium, whether or not intermixed or interalloyed; mercury. - Alkali or alkaline-earth metals : 2805.11 - - Sodium 2805.12 - - Calcium 2805.19 - - Other 2805.30 - Rare-earth metals, scandium and yttrium whether or not intermixed or interalloyed 2805.40 - Mercury (A) ALKALI METALS The five alkali metals are soft and rather light. They decompose cold water; they deteriorate in air, forming hydroxides. (1) Lithium. This is the lightest (specific gravity 0.54) and hardest of the group. It is kept in mineral oil or inert gases. Lithium helps to improve the qualities of metals, and is used in various alloys (e.g., anti-friction alloys). Because of its great affinity for other elements, it is also used, inter alia, to obtain other metals in the pure state. (2) Sodium. A solid (specific gravity 0.97) with a metallic lustre, readily tarnishing after cutting. It is preserved in mineral oil or in airtight welded tins. Sodium is obtained by electrolysing molten sodium chloride or sodium hydroxide. It is used in the manufacture of sodium peroxide (“ dioxide ”), sodium cyanide, sodamide, etc., the indigo industry, the manufacture of explosives (chemical primers and fuses), the polymerisation of butadiene, anti-friction alloys, or titanium or zirconium metallurgy. The heading excludes sodium amalgam (heading 28.53). (3) Potassium. A silvery-white metal (specific gravity 0.85), which can be cut with an ordinary knife. It is preserved in mineral oil or in sealed ampoules. Potassium is used for the preparation of certain photoelectric cells, and in anti-friction alloys.
    [Show full text]
  • Melting Points of the Iron Group Elements by a New Radiation Method
    MELTING POINTS OF THE IRON GROUP ELEMENTS BY A NEW RADIATION METHOD. By Geo. K. Burgess. Recently^ Dr. Waidner and the author suggested two radiation methods for the determination of high melting points of substances in minute quantities. The first depends on the total radiation from a surface as measured in terms of some instrument making use of the Stefan-Bolzmann law. The second method is based on the meas- urement of the intensit}^ of a particular monochromatic radiation from platinum or other substance; that is, it makes use of an instru- ment based on Wien's equation.^ Some preliminary measurements made at that time by the second method on the metals of the iron group showed it to possess consid- erable accuracy and to be particularly applicable to the easily oxi- dized elements if the melts were obtained in an atmosphere of pure hydrogen. It was also demonstrated that a compound of one of the refractory elements, which could be reduced to the metal by hydro- gen, might serve as material for determining the melting point of the pure metal. The present paper is an account of the application of this second method to the determination of the melting points in hydrogen of the members of the iron group, using, for the measurement of tem- perature a Holborn-Kurlbaum optical pyrometer, and the data on the monochromatic radiation from platinum published in this Bulletin.' ^Waidner and Burgess: On the Determination of Melting Points by Radiation Method, Phys. Rev., 22, p. 359; 1906. 2 A discussion of the laws of radiation will be found in this Bulletin, 1, p.
    [Show full text]
  • Search for Trans-Iron Elements in Hot, Helium-Rich White Dwarfs with the HST Cosmic Origins Spectrograph?,?? D
    A&A 612, A62 (2018) https://doi.org/10.1051/0004-6361/201732401 Astronomy & © ESO 2018 Astrophysics Search for trans-iron elements in hot, helium-rich white dwarfs with the HST Cosmic Origins Spectrograph?,?? D. Hoyer1, T. Rauch1, K. Werner1, and J.W. Kruk2 1 Institute for Astronomy and Astrophysics, Kepler Center for Astro and Particle Physics, Eberhard Karls University, Sand 1, 72076 Tübingen, Germany e-mail: [email protected] 2 NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA Received 2 December 2017 / Accepted 3 January 2018 ABSTRACT The metal abundances in the atmospheres of hot white dwarfs (WDs) entering the cooling sequence are determined by the preceding Asymptotic Giant Branch (AGB) evolutionary phase and, subsequently, by the onset of gravitational settling and radiative levitation. In this paper, we investigate three hot He-rich WDs, which are believed to result from a late He-shell flash. During such a flash, the He-rich intershell matter is dredged up and dominates the surface chemistry. Hence, in contrast to the usual H-rich WDs, their spectra allow direct access to s-process element abundances in the intershell that were synthesized during the AGB stage. In order to look for trans-iron group elements (atomic number Z > 29), we performed a non-local thermodynamic equilibrium model atmosphere analysis of new ultraviolet spectra taken with the Cosmic Origins Spectrograph aboard the Hubble Space Telescope. One of our program stars is of PG 1159 spectral type; this star, PG 1707+427, has effective temperature Teff = 85 000 K, and surface gravity log g = 7:5.
    [Show full text]
  • Penstoffe.12 the MOON, and MARS* Mercer, Paneth
    VOL. 41, 1955 CHEMISTRY: H. C. UREY 127 by the homogeneous behavior of native and enzymatically liberated maple lignins in electrophoresis, as contrasted with the indication of a secondary component in both these lignins by the paper-chromatographic technique. As a result of this study, lignins should be regarded as mixtures of components, all possessing similar structures but with the possibility of certain chemical differ- ences, as discussed above. It is for such mixtures of substances which may differ both in structure and in molecular size that Staudinger introduced the term Grup- penstoffe. 12 * Procter and Gamble Fellow. t Communication No. 293. Presented before the Division of Biological Chemistry of the American Chemical Society, New York, New York, September 13, 1954. This work was sup- ported by the National Science Foundation and the Office of Naval Research. For Communica- tions Nos. XII, XIII, and XIV of this series see notes 5, 8, and 11. 1 F. E. Brauns, in Ott and Spurlin (eds.), Cellulose and Cellulose Derivatives (New York: Interscience Publishers, Inc., 1954), I, 480. 2 F. F. Nord and W. J. Schubert, Holzforschung, 5, 1, 1951. 3 S. F. Kudzin and F. F. Nord, J. Am. Chem. Soc., 73, 690, 4619, 1951. 4 R. M. DeBaun and F. F. Nord, J. Am. Chem. Soc., 73, 1358, 1951. 5 G. de Stevens and F. F. Nord, these PROCEEDINGS, 39, 80, 1953. 6 G. de Stevens and F. F. Nord, Fortschr. chem. Forsch., 3, 70, 1954. 7 C. Schuerch, J. Am. Chem. Soc., 72, 3838, 1950. 8 W. J. Schubert, Holz, 12, 373, 1954.
    [Show full text]