| 1. |
- Bourdieu, Pierre, et al.
(författare)
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Leve idrottspedagogiken : En vänbok tillägnad Lars-Magnus Engström
- 2005
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- Vem ägnar sig åt idrott? Vilken betydelse har fritiden i barns och ungdomars liv? Vad innebär hälsa i skolämnet idrott och hälsa?Leve idrottspedagogiken! tillägnas Lars-Magnus Engström. Texterna i boken speglar delar av det idrottspedagogiska forskningsområdet i Sverige, vars framväxt Lars-Magnus Engström varit den främste företrädaren för. Läsaren får här ta del av exempelvis idrottskulturen, fritidskulturen och skolans ämne idrott och hälsa. Genomgående handlar texterna om villkoren för barns och ungdomars deltagane och om de olika lärprocesser som sker i anslutning till idrottsutövning.Lars-Magnus Engström har gjort betydande insatser som forskare och lärare samt som professor vid Lärarhögskolan i Stockholm och vid Gymnastik- och idrottshögskolan. I snart fyrtion år har han arbetat med studier kring påverkans- och lärprocesser i idrott. Hans forskning har främst kretsat kring människors idrottsvanor och vilka som utvecklar en fysiskt aktiv livsstil. Idrotts- och motionsutövningar ger både ett så kallat egenvärde och investeringsvärde. Med dessa begrepp bland många andra har Lars-Magnus Engström bidragit till en fördjupad vetenskaplig förståelse av idrottskulturen.De flesta författarna har eller har haft Lars-Magnus Engström som handledare och tillhör forskningsgruppen för pedagogik, idrott och fritidskultur. Redaktörer för boken är Karin Redelius och Håkan Larsson.
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| 2. |
- Gustafsson, Bengt, et al.
(författare)
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A grid of MARCS model atmospheres for late-type stars
- 2008
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 486:3, s. 951-970
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Forskningsöversikt (refereegranskat)abstract
- Context. In analyses of stellar spectra and colours, and for the analysis of integrated light from galaxies, a homogeneous grid of model atmospheres of late-type stars and corresponding flux spectra is needed. Aims. We construct an extensive grid of spherically-symmetric models (supplemented with plane-parallel ones for the highest surface gravities), built on up-to-date atomic and molecular data, and make it available for public use. Methods. The most recent version of the MARCS program is used. Results. We present a grid of about 104 model atmospheres for stars with 2500K <= T-eff <= 8000 K, -1 <= log g = log (GM/R-2) <= 5 (cgs) with various masses and radii, -5 <= [Me/H] <= + 1, with [alpha/Fe] = 0.0 and 0.4 and different choices of C and N abundances. This includes "CN-cycled" models with C/N=4.07 (solar), 1.5 and 0.5, C/O ranging from 0.09 to (normally) 5.0 to also represent stars of spectral types R, S and N, and with 1.0 <= xi(t) = 5km s(-1). We also list thermodynamic quantities (T, P-g, P-e, rho, partial pressures of molecules, etc.) and provide them on the World Wide Web, as well as calculated fluxes in approximately 108 000 wavelength points. Underlying assumptions in addition to 1D stratification (spherical or plane-parallel) include hydrostatic equilibrium, mixing-length convection and local thermodynamic equilibrium. We discuss a number of general properties of the models, in particular in relation to the effects of changing abundances, of blanketing, and of sphericity. We illustrate positive and negative feedbacks between sphericity and molecular blanketing. We compare the models with those of other available grids and find excellent agreement with planeparallel models of Castelli & Kurucz (if convection is treated consistently) within the overlapping parameter range. Although there are considerable departures from the spherically-symmetric NextGen models, the agreement with more recent PHOENIX models is gratifying. Conclusions. The models of the grid show considerable regularities, but some interesting departures from general patterns occur for the coolest models due to the molecular opacities. We have tested a number of approximate "rules of thumb" concerning effects of blanketing and sphericity and often found them to be astonishingly accurate. Some interesting new phenomena have been discovered and explored, such as the intricate coupling between blanketing and sphericity, and the strong effects of carbon enhancement on metal-poor models. We give further details of line absorption data for molecules, as well as details of models and comparisons with observations in subsequent papers.
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| 3. |
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| 4. |
- Jonsell, Karin, 1970-
(författare)
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Chemical Abundance Analysis of Population II Stars : The Summary Includes a Background in General Astronomy
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- We are made of stardust in the sense that most atomic nuclei around us have been formed by stars. Stars synthesise new elements and expel them to the interstellar medium, from which later new generations of stars are born. We can map this chemical evolution by analysing the atmospheric contents of old Galactic halo stars. I have done two such investigations. A vigourous debate is going on whether the oxygen-to-iron ratio varies strongly with the general metal-content of halo stars. In my first study, I made an abundance analysis of 43 halo stars, and found no support for such a variation. I have also found that there probably is a cosmic spread in the abundances of oxygen, magnesium, silicon, and calcium relative to iron for halo stars. This may be an indication that the halo was built up by subsystems with differences in the star formation rate. In my second study, I performed a thorough abundance analysis of the star HE0338-3945, which is strangely overabundant in both r- and s-elements. Several other stars have been found with abundance patterns curiously similar to this star, and I define new criteria for the class r+s stars. The abundance similarities among the r+s stars suggest a common formation scenario. However, as the s-elements usually are considered to be produced in binary systems of low mass, and r-elements in supernovae of Type II, this scenario is not obvious. In the article I discuss seven hypotheses, and several of them are dismissed.
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| 5. |
- Jonsell, Karin, et al.
(författare)
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Chemical abundances in 43 metal-poor stars
- 2005
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 440:1, s. 321-343
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Tidskriftsartikel (refereegranskat)abstract
- We have derived abundances of O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Fe, Ni, and Ba for 43 metal-poor field stars in the solar neighbourhood, most of them subgiants or turn-off-point stars with iron abundances [Fe/H] ranging from -0.4 to -3.0. About half of this sample has not been spectroscopically analysed in detail before. Effective temperatures were estimated from uvby photometry, and surface gravities primarily from Hipparcos parallaxes. The analysis is differential relative to the Sun, and was carried out with plane-parallel MARCS models. Various sources of error are discussed and found to contribute a total error of about 0.1-0.2 dex for most elements, while relative abundances, such as [Ca/Fe], are most probably more accurate. For the oxygen abundances, determined in an NLTE analysis of the 7774 Å triplet lines, the errors may be somewhat larger. We made a detailed comparison with similar studies and traced the reasons for the, in most cases, relatively small differences. Among the results we find that [O/Fe] possibly increases beyond [Fe/H] = -1.0, though considerably less so than in results obtained by others from abundances based on OH lines. We did not trace any tendency toward strong overionization of iron, and find the excesses, relative to Fe and the Sun, of the α elements Mg, Si, and Ca to be smaller than those of O. We discuss some indications that also the abundances of different α elements relative to Fe vary and the possibility that some of the scatter around the trends in abundances relative to iron may be real. This may support the idea that the formation of Halo stars occurred in smaller systems with different star formation rates. We verify the finding by Gratton et al. (2003b, A&A, 406, 131) that stars that do not participate in the rotation of the galactic disk show a lower mean and larger spread in [ α/Fe] than stars participating in the general rotation. The latter stars also seem to show some correlation between [ α/Fe] and rotation speed. We trace some stars with peculiar abundances, among these two Ba stars, HD 17072 and HD 196944, the second already known to be rich in s elements. Finally we advocate that a spectroscopic study of a larger sample of halo stars with well-defined selection criteria is very important, in order to add to the very considerable efforts that various groups have already made.
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| 6. |
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| 7. |
- Ryde, Nils, et al.
(författare)
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A First Study of Giant Stars in the Galactic Bulge based on Crires spectra
- 2007
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Ingår i: Stellar Populations as Building Blocks of Galaxies. ; , s. 260-261
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We present our on-going work on the determination of elemental abundances of giants in the Galactic Bulge by means of infrared spectroscopy. We show a preliminarily reduced spectrum and a synthetic spectrum fit of the Bulge giant Arp 4203 recorded with the near-infrared, high-resolution Crires spectrograph mounted on the VLT during its science verification run in August 2006. Abundances derived from this spectrum are discussed.
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| 8. |
- VandenBerg, Don A., et al.
(författare)
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A Constraint on Zsolar from Fits of Isochrones to the Color-Magnitude Diagram of M67
- 2007
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 666:2, s. L105-L108
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Tidskriftsartikel (refereegranskat)abstract
- The mass at which a transition is made between stars that have radiative or convective cores throughout the core H burning phase is a fairly sensitive function of Z (particularly, the CNO abundances). As a consequence, the ~4 Gyr, open cluster M67 provides a constraint on Zsolar (and the solar heavy-element mixture) because (1) high-resolution spectroscopy indicates that this system has virtually the same metal abundances as the Sun, and (2) its turnoff stars have masses just above the lower limit for sustained core convection on the main sequence. In this study, evolutionary tracks and isochrones using the latest MARCS model atmospheres as boundary conditions have been computed for 0.6-1.4 Msolar on the assumption of a metals mix (implying Zsolar~0.0125) based on the solar abundances derived by M. Asplund and collaborators using 3D model atmospheres. These calculations do not predict a turnoff gap where one is observed in M67. No such difficulty is found if the analysis uses isochrones for Zsolar=0.0165, assuming the Grevesse and Sauval mix of heavy elements. Our findings, like the inferences from helioseismology, indicate a problem with the abundances of Asplund and collaborators. However, it is possible that low-Z models with diffusive processes taken into account will be less problematic.
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| 9. |
- Vandenberg, Don A., et al.
(författare)
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On Stellar Models with Blanketed Atmospheres as Boundary Conditions
- 2007
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Ingår i: Stellar Populations as Building Blocks of Galaxies. ; , s. 23-27
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The impact on the predicted Teff scale of using the latest MARCS model atmospheres, instead of a fixed atmospheric structure (e.g., the gray T–τ relation) is examined. The former were fitted to stellar interior models at both the photosphere and at τ = 100 to determine the sensitivity of evolutionary tracks and isochrones for [Fe/H] = 0.0 and −2.0 to the chosen fitting point. In the case of solar abundances, the Teff of the giant branch varied by up to 100–150 K, depending on how the outer layers were treated. Much smaller variations were found for metal-poor giants (or main-sequence stars). Interestingly, models for the low solar Z favored by Asplund et al. (Z=0.0125) were unable to reproduce the gap near the turnoff in the C-M diagram of the old open cluster M 67, in contrast to models that assume Z=0.0188.
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| 10. |
- VandenBerg, Don A., et al.
(författare)
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On the use of blanketed atmospheres as boundary conditions for stellar evolutionary models
- 2008
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 675:1, s. 746-763
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Tidskriftsartikel (refereegranskat)abstract
- Stellarmodels have been computed for stars having [Fe/H] = 0.0 (assuming both the Grevesse & Sauval and Asplund et al. heavy-element mixtures) and -2.0 to determine the effects on the predicted T-eff scale of using boundary conditions derived from the latest MARCS model atmospheres. The latter were fitted in a fully consistent way to the interior models at the photosphere and at tau = 100: the resultant evolutionary sequences on the H-R diagram were found to be nearly independent of the chosen fitting point. Tracks were also computed in which the pressure at T = T-eff was obtained by integrating the hydrostatic equation together with either the classical gray T(tau, T-eff) relation or that derived by Krishna Swamy from an empirical solar atmosphere. Due to the effects of differences in the solar-calibrated values of the mixing-length parameter, alpha(MLT), very similar tracks were obtained for the different treatments of the atmosphere, except at solar abundances, where the models based on the Krishna Swamy T(tau, T-eff) relationship predicted similar to 150 K hotter giant branches than the others, in good agreement with the inferred temperatures of giants in the open cluster M67 from recent (V - K) -T-eff relations. Tracks that used new "scaled solar, differentially corrected'' MARCS atmospheres were found to agree well with those that employed the Krishna Swamy T(tau, T-eff) relationship, independently of the assumed metal abundance. (Gray atmospheres are quite different from MARCS models.) Fits of isochrones for [Fe/H] = -2.0 to the CMD of the globular cluster M68, as well as the possibility that alpha(MLT) varies with stellar parameters, are also discussed.
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