The faint Cepheids of the Small Magellanic Cloud: An evolutionary selection effect?

Cordier, Daniel; Goupil, M. J.; Lebreton, Y.

doi:10.1051/0004-6361:20031185

Cited by 20 publications

(29 citation statements)

References 37 publications

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“…The effect is larger in the SMC, amounting to ∼ 0.3 dex (vs. ∼ 0.2 dex in the LMC). This result is in agreement with the ones suggested by the evolutionary models of Cordier et al (2003) on the condition of instability strip crossing of low-luminosity Cepheids in the SMC. Also, the discrepancy between the pulsational and evolutionary ML relations (Beaulieu et al 2001) can be largely cured by assuming lower metallicities.…”

Section: Discussionsupporting

confidence: 92%

“…Currently it has been shown that the observed periods of the first/second overtone double-mode Cepheids in the Magellanic Clouds can be fitted only if we assume that the metallicities of these low-luminosity stars are lower than their fundamental/first overtone counterparts (Kovács 2006). This observation supports the earlier result of Cordier, Goupil & Lebreton (2003), suggesting that Cepheids cannot 'blue-loop' at low-luminosities in the SMC, unless they have systematically lower metallicities than the higher luminosity ones. Stimulated by the above results, the goal of the present study is to use the photometric metallicities in the investigation of the metallicity spread among the Magellanic Cloud Cepheids.…”

Section: Introductionsupporting

confidence: 91%

“…Based on the formal errors of the mean values, the differences in the overall metallicities seem to be significant and are exhibited in the same sense in both clouds. We note that: (i) the average photometric metallicities are quite close to the 'canonical' values (e.g., Udalski et al 1999); (ii) the derived lower metallicity for the SMC FO variables is the same as suggested by Cordier et al (2003) for the low-luminosity Cepheids.…”

Section: [Fe/h] Distributions In the Mcssupporting

confidence: 81%

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On the Cepheid Metallicity Dichotomy

Kovács

2009

EAS Publications Series

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Abstract. With the aid of stellar atmosphere models, we derive iron abundances [Fe/H] from the OGLE B, V , I photometry on the Magellanic Cloud Cepheids. We show that in both clouds the average metallicities of the first overtone variables are lower than those of the fundamental ones (by ∼ 0.2 and ∼ 0.3 dex in the LMC and SMC, respectively). Consequently, there is a correlation between the overall [Fe/H] and luminosity; the lower luminosity stars tend to be also of lower metallicity. These metallicity dependencies are concordant with the ones derived for the two types of double-mode Cepheids from pulsation theory. Yet another support of this dichotomy comes from the evolution theories that require lower metallicities for blue-looping lowluminosity stars than for high-luminosity ones. We also comment on the possibility of using period-luminosity-color relations to derive more accurate metallicities.

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Section: Discussionsupporting

confidence: 92%

Section: Introductionsupporting

confidence: 91%

Section: [Fe/h] Distributions In the Mcssupporting

confidence: 81%

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On the Cepheid Metallicity Dichotomy

Kovács

2009

EAS Publications Series

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“…They found that tracks with metallicity Z = 0.001 correctly reproduce the boundary of the Cepheids towards lower luminosity. According to Cordier et al (2003), Cepheids populating the faint bottom of the instability strip are likely to be metal-poor stars, while variables distributed throughout the instability strip should belong to populations of various metal contents. Romaniello et al (2008) derived direct measurements of the iron abundances of Galactic and Magellanic Cepheids from FEROS and UVES high-resolution and high signal-to noise spectra.…”

Section: Cepheidsmentioning

confidence: 99%

Scaled solar tracks and isochrones in a large region of theZ–Yplane

Bertelli¹,

Nasi²,

Girardi³

et al. 2009

A&A

252

348

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We extend our theoretical computations for low-mass stars to intermediate-mass and massive stars, for which few databases exist in the literature. Evolutionary tracks and isochrones are computed for initial masses 2.50−20 M for a grid of 37 chemical compositions with metal content Z between 0.0001 and 0.070 and helium content Y between 0.23 and 0.40 to enable users to obtain isochrones for ages as young as about 10 7 years and to simulate stellar populations with different helium-to-metal enrichment laws. The Padova stellar evolution code is identical to that used in the first paper of this series. Synthetic TP-AGB models allow stellar tracks and isochrones to be extended until the end of the thermal pulses along the AGB. We provide software tools for the bidimensional interpolation (in Y and Z) of the isochrones from very old ages down to about 10 7 years. This lower limit depends on chemical composition. The extension of the blue loops and the instability strip of Cepheid stars are compared and the Cepheid mass-discrepancy is discussed. The location of red supergiants in the H-R diagram is in good agreement with the evolutionary tracks for masses from 10 to 20 M . Tracks and isochrones are available in tabular form for the adopted grid of chemical compositions in the extended plane Z − Y in three photometric systems. An interactive web interface allows users to obtain isochrones of any chemical composition inside the provided Z − Y range and also to simulate stellar populations with different Y(Z) helium-to-metal enrichment laws.

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“…Several authors (Dolphin et al 2002(Dolphin et al , 2003Clementini et al 2003;Cordier et al 2003) have suggested that ACs are the natural extension of the Population I Classical Cepheids to lower metal contents and smaller masses. This suggestion is well supported by theoretical investigations (Marconi et al 2004, MFC;Caputo et al 2004, C04) where, based on the constraints provided by pulsation and evolutionary models, it is shown that Anomalous and Classical Cepheids define a common region in the M V -log P plane, with the former ones at lower luminosities and shorter periods, as actually observed in the dwarf irregular galaxy Leo A (Dolphin et al 2002).…”

Section: Introductionmentioning

confidence: 99%

Synthetic properties of bright metal-poor variables

Fiorentino

Limongi

Caputo

et al. 2006

A&A

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We present new grids of evolutionary models for the so-called "Anomalous" Cepheids (ACs), adopting Z = 0.0001 and various assumptions on the progenitor mass and mass-loss efficiency. These computations are combined with the results of our previous set of pulsation models and used to build synthetic populations of the predicted pulsators as well as to provide a Mass-Luminosity relation in the absence of mass-loss. We investigate the effect of mass-loss on the predicted boundaries of the instability strip and we find that the only significant dependence occurs in the Period-Magnitude plane, where the synthetic distribution of the pulsators is, on average, brighter by about 0.1 mag than the one in absence of mass-loss. Tight Period-Magnitude relations are derived in the K band for both fundamental and first overtone pulsators, providing a useful tool for distance evaluations with an intrinsic uncertainty of about 0.15 mag, which decreases to ∼0.04 mag if the mass term is taken into account. The constraints provided by the evolutionary models are used to derive evolutionary (i.e., mass-independent) Period-Magnitude-Color relations which provide distance determinations with a formal uncertainty of the order of ∼0.1 mag, once the intrinsic colors are well known. We also use model computations from the literature to investigate the effect of metal content both on the instability strip and on the evolutionary Period-Magnitude-Color relations. Finally, we compare our theoretical predictions with observed variables and we confirm that a secure identification of actual ACs requires simultaneous information on period, magnitude and color, that also provide constraints on the pulsation mode.

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The faint Cepheids of the Small Magellanic Cloud: An evolutionary selection effect?

Cited by 20 publications

References 37 publications

On the Cepheid Metallicity Dichotomy

On the Cepheid Metallicity Dichotomy

Scaled solar tracks and isochrones in a large region of theZ–Yplane

Synthetic properties of bright metal-poor variables

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