scholarly journals Horizontal Branch Evolution

1989 ◽  
Vol 111 ◽  
pp. 103-119 ◽  
Author(s):  
R.T. Rood ◽  
D.A. Crocker
Keyword(s):  
Horizontal Branch ◽  
Significant Progress ◽  
Period Shift ◽  
Shift Effect ◽  
Parameter Problem

AbstractIn 1973 the outstanding problems confronting the theory of horizontal branch evolution were the “second parameter” problem and the Oosterhoff Effect. Despite significant progress, particularly in the observations and in the observation/theory interface, they remain as the outstanding problems of 1988. The Oosterhoff Effect is now discussed primarily in the guise of the Sandage Period Shift Effect. The morphology of the HB seems more complicated than ever. E.g., many clusters show bimodal distributions along the HB. Here we will tentatively consider those to be manifestations of the second parameter problem. We will indicate why we feel that all previously suggested solutions have all been chimeras.

scholarly journals The Globular Cluster ω Centauri and its RR Lyrae Variables

1989 ◽  
Vol 111 ◽  
pp. 141-167
Author(s):  
R.J. Dickens
Keyword(s):  
Globular Cluster ◽  
Main Sequence ◽  
Red Giants ◽  
Horizontal Branch ◽  
Main Sequence Stars ◽  
Chemical Enrichment ◽  
Rr Lyrae ◽  
Stellar Pulsation ◽  
Stellar Ages ◽  
Period Shift

AbstractThe significance of some of the unusual characteristics of the globular cluster ω Centauri in various fundamental problems is explored. Interest is centred on the properties of the cluster RR Lyraes, and what they can contribute to studies of early cluster chemical enrichment, stellar pulsation, the distance scale, stellar evolution, stellar ages and the Oosterhoff period-shift problem. This article, which is intended to highlight problems and progress rather than give a comprehensive review, includes new results based on photometry of the RR Lyraes, red giants, subgiants, horizontal-branch and main sequence stars in the cluster.

scholarly journals CCD Photometry of RR Lyrae Stars in M3

1993 ◽  
Vol 139 ◽  
pp. 325-331
Author(s):  
C. Cacciari ◽  
E. Carretta ◽  
F. Ferraro ◽  
F. Fusi Pecci ◽  
G. Tessicini ◽  
...  
Keyword(s):  
Temperature Distribution ◽  
Ccd Photometry ◽  
Rr Lyrae Stars ◽  
Preliminary Results ◽  
Rr Lyrae ◽  
Period Shift ◽  
Shift Effect ◽  
Lyrae Stars

AbstractNew CCD BVI observations of RR Lyrae variables in M3 are presented. Mean magnitudes and colours are derived, as well as their relations with periods and amplitudes, and comparisons are made with previous data (Sandage 1981, 1990). Preliminary results are presented on the temperature distribution of the variables and the period-shift effect with respect to M15 and M68.

scholarly journals The ages of stars: The horizontal branch

2008 ◽  
Vol 4 (S258) ◽  
pp. 209-220 ◽  
Author(s):  
M. Catelan
Keyword(s):  
Recent Progress ◽  
Horizontal Branch ◽  
Parameter Problem

AbstractHorizontal branch (HB) stars play a particularly important role in the “age debate,” since they are at the very center of the long-standing “second parameter” problem. In this review, I discuss some recent progress in our understanding of the nature and origin of HB stars.

On the interpretation of the Sandage period-shift effect among globular-cluster RR Lyrae variables

1987 ◽  
Vol 312 ◽  
pp. 762 ◽  
Author(s):  
Allen V. Sweigart ◽  
Alvio Renzini ◽  
Amedeo Tornambe
Keyword(s):  
Globular Cluster ◽  
Rr Lyrae ◽  
Period Shift ◽  
Shift Effect

scholarly journals RR Lyrae Stars and the Sandage Period-Shift Effect Examined Using IR-Derived Temperatures

1989 ◽  
Vol 111 ◽  
pp. 274-274
Author(s):  
A.J. Longmore ◽  
R. Dixon ◽  
I. Skillen ◽  
R.F. Jameson ◽  
J.A. Fernley
Keyword(s):  
Globular Clusters ◽  
Log P ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Period Shift ◽  
Observational Errors ◽  
Shift Effect ◽  
Few Data ◽  
Lyrae Stars ◽  
Temperature Amplitude

AbstractMean temperatures for RR Lyrae stars in 7 globular clusters (M3, M4, M5, M15, M107, ω Cen and NGC 5466) have been determined using the optical-infrared colour <V>-<K> as a temperature indicator. Where <K> has been relatively well determined, from means of 3 or more observations, the scatter in relationships such as Log P’ vs log (temperature) and log (temperature) vs (blue amplitude) is significantly reduced when IR-derived temperatures are used instead of those derived from (B-V). Within the observational errors, the gradient in the log P’ vs log (temperature) diagram is the same for each cluster. Temperatures derived from <V>-<K> should also be less sensitive to metallicity differences than their optically derived counterparts. The Sandage Period-Shift Effect has therefore been re-examined using 6 of the 7 clusters (NGC 5466 was excluded because of too few data). A strong correlation between period-shift and metallicity is found; a smaller shift (but in the same sense) is also found for the temperature – amplitude relationship.

Toward quantitative defect analysis using HREM

1994 ◽  
Vol 52 ◽  
pp. 714-715
Author(s):  
David J. Smith
Keyword(s):  
Electron Microscope ◽  
Unit Cell ◽  
Defect Analysis ◽  
Significant Progress ◽  
Detailed Characterization ◽  
Small Unit ◽  
Resolution Electron ◽  
High Resolution Electron Microscope ◽  
Large Unit Cell ◽  
Made In

The electron microscope has evolved to the level where it is now straightforward to record highresolution images from thin samples (t∼10 to 20nm) that are directly interpretable in terms of atomic arrangements. Whilst recorded images necessarily represent two-dimensional projections of the structure, many defects such as dislocations and interfaces may be linear or planar in nature and thus might be expected to be amenable to detailed characterization. In this review, we briefly consider the recent significant progress that has been made in quantitative defect analysis using the high-resolution electron microscope and then discuss some drawbacks to the technique as well as potential scope for further improvements. Surveys of defect modelling for some small-unit-cell materials and interfaces have recently been published, and reference should be made to other papers in this symposium for further examples.The technique of structure imaging originated in the early '70s with observations of large-unit-cell block oxides.

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