| 1. |
- Christlieb, Norbert, et al.
(författare)
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New Searches for R-Process Enhanced Stars
- 2001
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Ingår i: Proceedings of "Astrophysical Ages and Times Scales", ASP Conference Series. - : Astronomical Society of the Pacific, San Francisco, U.S.A.. - 1583810838 ; , s. 298-300
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We discuss strategies for the detection of additional examples of highly r-process-enhanced, ultra-metal-poor stars, such as the two presently known examples of the class, CS~22892-052, and the newly discovered CS~31082-001. We expect that a quick, modera
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| 2. |
- EDVARDSSON, Bengt, et al.
(författare)
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ABUNDANCE ANALYSIS AND ORIGIN OF THE ZETA-SCULPTORIS OPEN CLUSTER
- 1995
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Ingår i: ASTRONOMY AND ASTROPHYSICS. - : SPRINGER VERLAG. - 0004-6361. ; 293:1, s. 75-86
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Tidskriftsartikel (refereegranskat)abstract
- We have determined chemical abundances and radial velocities for stars in the field of the zeta Sculptoris cluster. We find that the cluster metal deficiency previously found from UBV photometry is not supported; the cluster overall metallicity, [Fe/H] =
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| 3. |
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| 4. |
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| 5. |
- Flemme, Inger, et al.
(författare)
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Life situation of patients with an implantable cardioverter defibrillator : a descriptive longitudinal study
- 2001
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Ingår i: Journal of Clinical Nursing. - : Wiley. - 0962-1067 .- 1365-2702. ; 10:4, s. 563-572
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Tidskriftsartikel (refereegranskat)abstract
- • The aim of this study was to describe changes in the life situation of patients with an implantable cardioverter defibrillator over a period of 1 year. A sample of 56 consecutive patients took part in the study.• Life situation was measured through uncertainty in illness, satisfaction, and fear of the life situation. Descriptive statistics were used to present results, and analytical statistics were used to map out changes over time.• Overall uncertainty showed a decrease over time. A statistically significant difference was found within the domain uncertainty related to information (P < 0.001).• Satisfaction increased within the domains health-functioning, socio-economic, psychological–spiritual, and family.• The ability to act within the domain health-functioning showed a statistical significance (P < 0.05).• The domain life changes within fear in the life situation decreased and showed a statistical significance (P < 0.05).• The overall life situation showed increased satisfaction as well as lower uncertainty and fear in the life situation.• The research indicates that patients need more information about changes in the life situation after the implantable cardioverter defibrillator-implantation. The study encourages more humanistic, holistic research about patients’ life situations as well as more education in teaching skills for health care personnel.
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| 6. |
- Garcia, Lopez Ramon J, et al.
(författare)
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Boron in very metal-poor stars
- 1998
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Ingår i: ASTROPHYSICAL JOURNAL. - : UNIV CHICAGO PRESS. - 0004-637X. ; 500:1, s. 241-256
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Tidskriftsartikel (refereegranskat)abstract
- We have observed the B I lambda 2497 line to derive the boron abundances of two very metal-poor stars selected to help in tracing the origin and evolution of this element in the early Galaxy: BD +23 degrees 3130 and HD 84937. The observations were conduct
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| 7. |
- 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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| 8. |
- Gustafsson, Bengt, et al.
(författare)
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A new MARCS Grid
- 2002
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Ingår i: International Astronomical Union Symposium. - 1583811605 ; , s. A2-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- An extensive grid of spherically symmetric model atmospheres of stars with 1. 2500 K <= Teff <= 8000 K, 2. -1.0 <= log g (= log GM/R2) <= 5.0 (cgs units), 3. different combinations of M and R, 4. -5 <= [A/H] <= 1, and 5. a number of CNO abundance combinat
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| 9. |
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| 10. |
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| 11. |
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| 12. |
- 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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| 13. |
- 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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| 14. |
- Meszaros, Sz., et al.
(författare)
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New ATLAS9 and MARCS Model Atmosphere Grids for the Apache Point Observatory Galactic Evolution Experiment (APOGEE)
- 2012
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Ingår i: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 144:4, s. 120-
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Tidskriftsartikel (refereegranskat)abstract
- We present a new grid of model photospheres for the SDSS-III/APOGEE survey of stellar populations of the Galaxy, calculated using the ATLAS9 and MARCS codes. New opacity distribution functions were generated to calculate ATLAS9 model photospheres. MARCS models were calculated based on opacity sampling techniques. The metallicity ([M/H]) spans from -5 to 1.5 for ATLAS and -2.5 to 0.5 for MARCS models. There are three main differences with respect to previous ATLAS9 model grids: a new corrected H2O line list, a wide range of carbon ([C/M]) and alpha element [alpha/M] variations, and solar reference abundances from Asplund et al. The added range of varying carbon and alpha-element abundances also extends the previously calculated MARCS model grids. Altogether, 1980 chemical compositions were used for the ATLAS9 grid and 175 for the MARCS grid. Over 808,000 ATLAS9 models were computed spanning temperatures from 3500 K to 30,000 K and log g from 0 to 5, where larger temperatures only have high gravities. The MARCS models span from 3500 K to 5500 K, and log g from 0 to 5. All model atmospheres are publicly available online.
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| 15. |
- Plez, Bertrand, et al.
(författare)
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A MARCS Grid of S-type Star Atmospheres
- 2003
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Ingår i: International Astronomical Unium Symposium. - 1583811605 ; , s. A2-
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Konferensbidrag (populärvet., debatt m.m.)
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| 16. |
- 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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| 17. |
- Ryde, Nils, et al.
(författare)
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Chemical abundances of 11 bulge stars from high-resolution, near-IR spectra
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 509:1, s. A20-
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Tidskriftsartikel (refereegranskat)abstract
- Context. It is debated whether the Milky Way bulge has characteristics more similar to those of a classical bulge than those of a pseudobulge. Detailed abundance studies of bulge stars are important when investigating the origin, history, and classification of the bulge. These studies provide constraints on the star-formation history, initial mass function, and differences between stellar populations. Not many similar studies have been completed because of the large distance and high variable visual extinction along the line-of-sight towards the bulge. Therefore, near-IR investigations can provide superior results. Aims. To investigate the origin of the bulge and study its chemical abundances determined from near-IR spectra for bulge giants that have already been investigated with optical spectra. The optical spectra also provide the stellar parameters that are very important to the present study. In particular, the important CNO elements are determined more accurately in the near-IR. Oxygen and other alpha elements are important for investigating the star-formation history. The C and N abundances are important for determining the evolutionary stage of the giants and the origin of C in the bulge. Methods. High-resolution, near-infrared spectra in the H band were recorded using the CRIRES spectrometer mounted on the Very Large Telescope. The CNO abundances are determined from the numerous molecular lines in the wavelength range observed. Abundances of the alpha elements Si, S, and Ti are also determined from the near-IR spectra. Results. The abundance ratios [O/Fe], [Si/Fe], and [S/Fe] are enhanced to metallicities of at least [Fe/H] = -0.3, after which they decline. This suggests that the Milky Way bulge experienced a rapid and early burst of star formation similar to that of a classical bulge. However, a similarity between the bulge trend and the trend of the local thick disk seems to be present. This similarity suggests that the bulge could have had a pseudobulge origin. The C and N abundances suggest that our giants are first-ascent red-giants or clump stars, and that the measured oxygen abundances are those with which the stars were born. Our [C/Fe] trend does not show any increase with [Fe/H], which is expected if W-R stars contributed substantially to the C abundances. No "cosmic scatter" can be traced around our observed abundance trends: the measured scatter is expected, given the observational uncertainties.
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| 18. |
- Thoren, Patrik, et al.
(författare)
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Subgiants as probes of galactic chemical evolution
- 2004
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Ingår i: Astronomy & Astrophysics. - 0004-6361. ; 425:1, s. 187-206
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Tidskriftsartikel (refereegranskat)abstract
- Chemical abundances for 23 candidate subgiant stars have been derived with the aim at exploring their usefulness for studies of galactic chemical evolution. High-resolution spectra from ESO CAT-CES and NOT-SOFIN covered 16 different spectral regions in the visible part of the spectrum. Some 200 different atomic and molecular spectral lines have been used for abundance analysis of approximately 30 elemental species. The wings of strong, pressure-broadened metal lines were used for determination of stellar surface gravities, which have been compared with gravities derived from Hipparcos parallaxes and isochronic masses. Stellar space velocities have been derived from Hipparcos and Simbad data, and ages and masses were derived with recent isochrones. Only 12 of the stars turned out to be subgiants, i.e. on the "horizontal" part of the evolutionary track between the dwarf- and the giant stages. The abundances derived for the subgiants correspond closely to those of dwarf stars. With the possible exceptions of lithium and carbon we find that subgiant stars show no "chemical" traces of post-main-sequence evolution and that they are therefore very useful targets for studies of galactic chemical evolution.
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| 19. |
- Tomkin, Jocelyn, et al.
(författare)
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The rise and fall of the NaMgAl stars
- 1997
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Ingår i: ASTRONOMY AND ASTROPHYSICS. - 0004-6361. ; 327:2, s. 587-597
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Tidskriftsartikel (refereegranskat)abstract
- We have made new abundance determinations for a sample of NaMgAl stars. These stars, which are a subgroup of the nearby metal-rich field F and G disk dwarfs, were first identified by Edvardsson et al. (1993) on the basis of their apparent enrichment in Na, Mg and Al relative to other elements. The discovery of a planetary companion to the nearby solar type star 51 Peg (Mayor & Queloz 1995) combined with Edvardsson et al.'s earlier identification of 51 Peg as a NaMgAl star highlighted the group's potential importance. Our new analysis, which uses new spectra of higher resolution and better wavelength coverage than the analysis of Edvardsson et al., shows that the Na, Mg and Al abundances of the NaMgAl stars are indistinguishable from those of non-NaMgAl stars with otherwise similar properties. The group thus appears to be spurious.Our study, which includes 51 Peg, also provides the most complete set of abundances for this star available to date. The new Fe abundance, [Fe/H] = +0.20 +- 0.07, of 51 Peg confirms earlier measurements of its metal richness. Abundances for 19 other elements, including C, N and O, reveal a fairly uniform enrichment similar to that of Fe and show no evidence of abnormality compared to other metal rich stars of similar spectral type.
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| 20. |
- Van Eck, Sophie, et al.
(författare)
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A grid of MARCS model atmospheres for late-type stars II. S stars and their properties
- 2017
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 601
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Tidskriftsartikel (refereegranskat)abstract
- S-type stars are late-type giants whose atmospheres are enriched in carbon and s-process elements because of either extrinsic pollution by a binary companion or intrinsic nucleosynthesis and dredge-up on the thermally-pulsing asymptotic giant branch. A grid of MARCS model atmospheres has been computed for S stars, covering the range 2700 <= T-eff (K) <= 4000, 0.50 <= C/O less than or similar to 0.99, 0 <= log g <= 5, [Fe/H] = 0., -0.5 dex, and [s/Fe] = 0, 1, and 2 dex (where the latter quantity refers to the global overabundance of s-process elements). The MARCS models make use of a new ZrO line list. Synthetic spectra computed from these models are used to derive photometric indices in the Johnson and Geneva systems, as well as TiO and ZrO band strengths. A method is proposed to select the model best matching any given S star, a non-trivial operation since the grid contains more than 3500 models covering a five-dimensional parameter space. The method is based on the comparison between observed and synthetic photometric indices and spectral band strengths, and has been applied on a vast subsample of the Henize sample of S stars. Our results confirm the old claim by Piccirillo (1980, MNRAS, 190, 441) that ZrO bands in warm S stars (T-eff > 3200 K) are not caused by the C /O ratio being close to unity, as traditionally believed, but rather by some Zr overabundance. The TiO and ZrO band strengths, combined with V - K and J - K photometric indices, are used to select T-eff, C/O, [Fe/H] and [s/Fe]. The Geneva U - B1 and B2 - V1 indices (or any equivalent) are good at selecting the gravity. The defining spectral features of dwarf S stars are outlined, but none is found among the Henize S stars. More generally, it is found that, at T-eff = 3200 K, a change of C/O from 0.5 to 0.99 has a strong impact on V - K (2 mag). Conversely, a range of 2 mag in V - K corresponds to a 200 K shift along the (T-eff, V - K) relationship (for a fixed C/O value). Hence, the use of a (T-eff, V - K) calibration established forMstars will yield large errors for S stars, so that a specific calibration must be used, as provided in the present paper. Using the atmospheric parameters derived by our method for the sample of Henize S stars, we show that the extrinsic-intrinsic dichotomy among S stars reveals itself very clearly as a bimodal distribution in the e ff ective temperatures. Moreover, the increase of s-process element abundances with increasing C/O ratios and decreasing temperatures is apparent among intrinsic stars, confirming theoretical expectations.
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| 21. |
- van Eck, S., et al.
(författare)
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A Grid of MARCS Model Atmospheres for S Stars
- 2011
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Ingår i: Why Galaxies Care about AGB Stars II.
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Konferensbidrag (refereegranskat)abstract
- S-type stars are late-type giants whose atmospheres are enriched in carbon and s-process elements because of either extrinsic pollution by a binary companion or intrinsic nucleosynthesis and dredge-up on the thermally-pulsing AGB. A large grid of S-star model atmospheres has been computed covering the range 2700 \le T$_eff$(K) \le 4000 with 0.5 \le C/O \le 0.99. ZrO and TiO band strength indices as well as VJHKL photometry are needed to disentangle T$_eff$, C/O and [s/Fe]. A \ldquobest-model finding tool\rdquo has been developed using a set of well-chosen indices and checked against photometry as well as low- and high-resolution spectroscopy. It is found that applying M-star model atmospheres (i.e., with a solar C/O ratio) to S stars can lead to errors in T$_eff$ up to 400 K. We constrain the parameter space occupied by the S stars of the vast Henize sample in terms of T$_eff$, [C/O] and [s/Fe].
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| 22. |
- Van Eck, Sophie, et al.
(författare)
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A Grid of MARCS Model Atmospheres for S Stars
- 2011
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Ingår i: Astronomical Society of the Pacific, Conference Series, Volume 445. ; , s. 71-75
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Konferensbidrag (refereegranskat)abstract
- S-type stars are late-type giants whose atmosphere is enriched in carbon and s-process elements because of either extrinsic pollution by a binary companion or intrinsic nucleosynthesis and dredge-up on the thermally-pulsing AGB. A large grid of S-star model atmospheres has been computed covering the range 2700 < Teff < 4000 K with 0.5 < C/O < 0.99. ZrO and TiO band strength indices as well as VJHKL photometry are needed to disentangle Teff, C/O and [s/Fe]. A "best-model finding tool" was developed using a set of well-chosen indices and checked against photometry as well as low- and high-resolution spectroscopy. It is found that applying M-star model atmospheres (i.e., with a solar C/O ratio) to S stars can lead to errors on Teff up to 400K. We constrain the parameter space occupied by S stars of the vast sample of Henize stars in terms of Teff, [C/O] and [s/Fe].
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| 23. |
- Van Eck, S., et al.
(författare)
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A grid of S stars MARCS model atmospheres
- 2011
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Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 328, s. 012009-
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Tidskriftsartikel (refereegranskat)abstract
- S stars are cool stars of temperatures similar to those of M giants, but their atmospheres are enriched in carbon and s-process elements because of either extrinsic pollution by a binary companion or intrinsic nucleosynthesis and dredge-up on the thermally-pulsing AGB. Despite numerous attempts to link phenomenological spectral classification criteria to physical parameters (T$_eff$, gravity, C/O, [s/Fe], [Fe/H]), the parameter space of S stars is poorly known and this has prevented accurate abundance analysis of S stars until now. Here we present a large grid of S-star model atmospheres. ZrO and TiO band strength indices as well as VJHKL photometry are needed to disentangle the effective temperature, C/O and [s/Fe]. The stellar parameters derived on the basis of low-resolution spectra and photometry are shown to be fairly accurate when compared to high-resolution data of the same stars. The C/O ratio of S stars is found to be between the solar value (0.5) and 0.99, and not 1 as often claimed in the literature. Consistently with stellar evolution expectations, the C/O ratio increases as the effective temperature decreases.
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| 24. |
- 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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| 25. |
- 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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