The period-shift effect in Oosterhoff type II globular clusters with blue horizontal-branch morphologies

1994 ◽  
Vol 107 ◽  
pp. 2077 ◽  
Author(s):  
Marcio Catelan
Keyword(s):  
Globular Clusters ◽  
Type Ii ◽  
Horizontal Branch ◽  
Period Shift ◽  
Shift Effect

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 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.

Super-Helium-rich Populations and the Origin of Extreme Horizontal-Branch Stars in Globular Clusters

2005 ◽  
Vol 621 (1) ◽  
pp. L57-L60 ◽  
Author(s):  
Young-Wook Lee ◽  
Seok-Joo Joo ◽  
Sang-Il Han ◽  
Chul Chung ◽  
Chang H. Ree ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Horizontal Branch ◽  
Horizontal Branch Stars

scholarly journals Study of the Helium Enrichment in Globular Clusters

2009 ◽  
Vol 5 (S262) ◽  
pp. 27-30
Author(s):  
Aldo A. R. Valcarce ◽  
Márcio Catelan
Keyword(s):  
High Precision ◽  
Globular Clusters ◽  
Stellar Populations ◽  
Horizontal Branch ◽  
Previous Generation ◽  
Horizontal Branch Stars

AbstractGlobular clusters (GCs) are spheroidal concentrations typically containing of the order of 105 to 106, predominantly old, stars. Historically, they have been considered as the closest counterparts of the idealized concept of “simple stellar populations.” However, some recent observations suggest than, at least in some GCs, some stars are present that have been formed with material processed by a previous generation of stars. In this sense, it has also been suggested that such material might be enriched in helium, and that blue horizontal branch stars in some GCs should accordingly be the natural progeny of such helium-enhanced stars. In this contribution we show that, at least in the case of M3 (NGC 5272), the suggested level of helium enrichment is not supported by the available, high-precision observations.

scholarly journals Horizontal branch morphology: A new photometric parametrization

2019 ◽  
Vol 629 ◽  
pp. A53 ◽  
Author(s):  
M. Torelli ◽  
G. Iannicola ◽  
P. B. Stetson ◽  
I. Ferraro ◽  
G. Bono ◽  
...  
Keyword(s):  
Metal Content ◽  
Globular Clusters ◽  
Linear Trend ◽  
Cumulative Number ◽  
Horizontal Branch ◽  
Imaging Data ◽  
Galactic Globular Clusters ◽  
Absolute Age ◽  
Advanced Camera For Surveys ◽  
Branch Morphology

Context. Theory and observations indicate that the distribution of stars along the horizontal branch of Galactic globular clusters mainly depends on the metal content. However, the existence of globular clusters with similar metal content and absolute age but different horizontal branch morphologies, suggests the presence of another parameter affecting the star distribution along the branch. Aims. To investigate the variation of the horizontal branch morphology in Galactic globular clusters, we define a new photometric horizontal branch morphology index, overcoming some of the limitations and degeneracies affecting similar indices available in the literature. Methods. We took advantage of a sample of 64 Galactic globular clusters, with both space-based imaging data (Advanced Camera for Surveys survey of Galactic globular clusters) and homogeneous ground-based photometric catalogues in five different bands (U, B, V, R, I). The new index, τHB, is defined as the ratio between the areas subtended by the cumulative number distribution in magnitude (I) and in colour (V − I) of all stars along the horizontal branch. Results. This new index shows a linear trend over the entire range in metallicity (−2.35 ≤ [Fe/H] ≤ −0.12) covered by our Galactic globular cluster sample. We found a linear relation between τHB and absolute cluster ages. We also found a quadratic anti-correlation with [Fe/H], becoming linear when we eliminate the age effect on τHB values. Moreover, we identified a subsample of eight clusters that are peculiar according to their τHB values. These clusters have bluer horizontal branch morphology when compared to typical ones of similar metallicity. These findings allow us to define them as the ’second parameter’ clusters in the sample. A comparison with synthetic horizontal branch models suggests that they cannot be entirely explained with a spread in helium content.

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