Theoretical Models for Classical Cepheids. VIII. Effects of Helium and Heavy‐Element Abundance on the Cepheid Distance Scale

A number of recent investigations have demonstrated that the heavy element abundance in galactic disks decreases with increasing distance from the center. Although there is little question that the composition in the outermost parts of galactic disks differs from that in the inner regions, the precise nature of the presumed gradient in our own galaxy remains undetermined. At the present time, the most specific evidence for a gradient is based either on kinematics of stars in the solar vicinity (e.g., Janes, 1975 or Mayor, 1976) or on observations of distant H II regions (Hawley, 1977) and planetary nebulae (Peimbert, et al, 1977). Little is known about the variation of abundance ratios with position or the relation between stellar ages and the composition gradient. However, all three of these quantities (that is, the overall metallicity gradient, variation of abundance ratios and stellar age effects) can now be estimated from theoretical models of galactic evolution (for example, see Tinsley and Larson, 1977).

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Effects of Heavy-Element Abundance on Classification of G-Type Giants

Abundance Effects in Classification ◽

10.1007/978-94-010-1476-2_26 ◽

1976 ◽

pp. 147-147

Author(s):

P. C. Keenan

Keyword(s):

Heavy Element ◽

Element Abundance

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A Spectroscopic Survey in the EUV of the “Coolest” Hot DA Stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100036009 ◽

1996 ◽

Vol 152 ◽

pp. 217-222

Author(s):

Jean Dupuis ◽

Stéphane Vennes

Keyword(s):

Effective Temperature ◽

White Dwarfs ◽

Heavy Element ◽

Extreme Ultraviolet ◽

Diffusion Theory ◽

Hydrogen Atmosphere ◽

Element Abundance ◽

Pure Hydrogen ◽

Element Abundances ◽

The One

We present an analysis of the extreme ultraviolet (EUV) spectroscopy of a sample of 10 DA white dwarfs observed by the Extreme Ultraviolet Explorer (EUVE). We have selected white dwarfs cooler than about 50,000 K and with presumably low heavy element abundances. The goal of this study is to determine the fundamental atmospheric parameters, namely the effective temperature and chemical composition, of these stars by fitting their continua with synthetic spectra computed from pure hydrogen LTE/line-blanketed model atmospheres. The question of the presence (or absence) of trace elements is explored by comparing EUV-determined effective temperatures to the one obtained from a fit of hydrogen balmer lines. It is found that the majority of the DA in the sample are consistent with having a pure hydrogen atmosphere. One of the star, MCT0027-634, is another possible example of a HZ 43-type white dwarf, having an effective temperature above 50000 K and a low heavy element abundance, i.e., much lower than predicted by diffusion theory.

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Supernova Abundance Generation

Symposium - International Astronomical Union ◽

10.1017/s007418090022723x ◽

1991 ◽

Vol 145 ◽

pp. 21-38

Author(s):

K. Nomoto ◽

T. Shigeyama ◽

T. Tsujimoto

Keyword(s):

Heavy Element ◽

Massive Stars ◽

Theoretical Models ◽

Light Curves ◽

Maximum Brightness ◽

Sn 1987A ◽

New Models ◽

Decline Rate ◽

Type Ia ◽

Supernova Explosions

Theoretical models of supernova explosions of various types are reviewed to obtain heavy element yields from supernovae. We focus on new models for SN 1987A, and Type Ia, Ib, and Ic supernovae. Maximum brightness and decline rate of their light curves suggest that 12–18 M⊙ stars produce larger amount of 56Ni than more massive stars. We discuss relative roles of various types of supernovae in the chemical evolution of galaxies.

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Uncertainties in the Position of the β Cephei Instability Strip in the HR Diagram

International Astronomical Union Colloquium ◽

10.1017/s0252921100037155 ◽

1995 ◽

Vol 155 ◽

pp. 291-292

Author(s):

A.A. Pamyatnykh ◽

W.A. Dziembowski ◽

P. Mikołaj

Keyword(s):

Heavy Element ◽

Element Abundance ◽

Instability Strip ◽

Metal Mixture ◽

Hr Diagram

AbstractWe discuss the sensitivity of the theoretical B star instability domains to the heavy element abundance Z, the adopted metal mixture, the assumed overshooting from stellar convective cores and the choice of the opacity data.

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Theoretical Models of W Virginis Variables

International Astronomical Union Colloquium ◽

10.1017/s025292110010942x ◽

1985 ◽

Vol 82 ◽

pp. 246-249

Author(s):

Alan Bridger

Keyword(s):

Theoretical Models ◽

Stellar Mass ◽

Theoretical Studies ◽

Classical Cepheids

W Virginis variables are the population II counterparts of the classical cepheids, although they do not show quite the same trends as are seen in the latter. Theoretical studies of the population II cepheids have not been very extensive until recent studies of the shorter period variables (BL Herculis variables, with periods between 1 and 10 days). The variables with periods above 10 days (up to about 50 days) have only been studied by a few authors, modelling the prototype star (W Vir) (.g. Christy 1966; Davis 1974). Although these models qualitatively reproduced the observations they were not very successful, and were based on a stellar mass (0.88 Mʘ) that now seems likely to be too high.

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Element Abundance Analyses of Novae

International Astronomical Union Colloquium ◽

10.1017/s0252921100069438 ◽

1977 ◽

Vol 42 ◽

pp. 242-273 ◽

Cited By ~ 1

Author(s):

Robert E. Williams

Keyword(s):

Temperature Distribution ◽

Emission Line ◽

Heavy Element ◽

Element Abundance ◽

Element Abundances ◽

Maximum Light ◽

Growth Studies ◽

Nova Shells

AbstractThe different methods by which element abundances in novae have been determined are reviewed. Curve of growth studies of novae at maximum light have indicated CNO nuclei to be greatly enhanced with respect to hydrogen in certain objects. These results are questionable because they depend upon an assumed temperature distribution in the photosphere which is probably too steep to be realistic. Emission line analyses of novae, generally obtained in the period of early decline, also indicate possible heavy element enhancement, however these results are tentative because of uncertainties in the parameters of the emitting gas. It is suggested that useful abundance determinations of nova ejecta might be obtained from studies of old, extended nova shells.

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Cepheid distances from the Baade–Wesselink method

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312021266 ◽

2012 ◽

Vol 8 (S289) ◽

pp. 138-144 ◽

Cited By ~ 1

Author(s):

Wolfgang Gieren ◽

Jesper Storm ◽

Nicolas Nardetto ◽

Alexandre Gallenne ◽

Grzegorz Pietrzyński ◽

...

Keyword(s):

Excellent Agreement ◽

Surface Brightness ◽

Recent Progress ◽

Main Sequence ◽

Near Infrared ◽

Open Cluster ◽

Open Clusters ◽

Distance Scale ◽

Systematic Uncertainties ◽

Classical Cepheids

AbstractRecent progress on Baade–Wesselink (BW)-type techniques to determine the distances to classical Cepheids is reviewed. Particular emphasis is placed on the near-infrared surface-brightness (IRSB) version of the BW method. Its most recent calibration is described and shown to be capable of yielding individual Cepheid distances accurate to 6%, including systematic uncertainties. Cepheid distances from the IRSB method are compared to those determined from open cluster zero-age main-sequence fitting for Cepheids located in Galactic open clusters, yielding excellent agreement between the IRSB and cluster Cepheid distance scales. Results for the Cepheid period–luminosity (PL) relation in near-infrared and optical bands based on IRSB distances and the question of the universality of the Cepheid PL relation are discussed. Results from other implementations of the BW method are compared to the IRSB distance scale and possible reasons for discrepancies are identified.

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