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Astron. Astrophys. 363, 601-604 (2000)

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2. Nonlinear Cepheid models

The overall strategy of nonlinear model construction was the same as that discussed in Aikawa & Antonello (2000; hereinafter Paper I). The adopted chemical composition was [FORMULA], [FORMULA] and [FORMULA], and the opacity (s92 364) was that supplied by the OP project (Seaton et al. 1994), with OPTFIT code (Seaton 1993) for fitting and smoothing of the opacity tables. We assumed the M-L relation suggested by Chiosi (1990) for full convective overshooting evolutionary models, modified according to more recent models (see Paper I).

[EQUATION]

Another relation was assumed for comparison purposes:

[EQUATION]

It was obtained simply by shifting the zero point in relation (1) in the way required by Wood et al. (1997) to explain the light curve of HV 905 in LMC. The theoretical blue edge was calculated with linear nonadiabatic LNA analysis using Castor's type code for a given mass and the corresponding luminosity, and the values of the effective temperature [FORMULA] of the model sequences were chosen 200 K and 400 K smaller than the corresponding blue edge. We will call the model sequence obtained with Eqs. (1) and (2) as sequence (a) and (b), respectively. Fig. 1 shows the location of the sequences in the log[FORMULA]-logL diagram along with the blue edges of the fundamental mode and the resonance line [FORMULA] that we expect from linear period ratios. Sequence (a) has a mass range [FORMULA] and covers pulsation periods from about 7 to 155 days. Similarly, the mass range of sequence (b) is [FORMULA], and it covers almost the same range of pulsation periods as sequence (a). For other features of nonlinear modeling, see Paper I.

[FIGURE] Fig. 1. The location of model sequences in the HR diagram; sequence(a) was obtained with the M-L relation (1), sequence(b) with the relation (2). The sequences, which are indicated by plus signs, were obtained for [FORMULA] which was 200 K and 400 K lower than the corresponding blue edge. The resonance line [FORMULA] (linear period ratio; dotted line), some periods of the models and the blue edge of the F-mode (continuous line) are also indicated.

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© European Southern Observatory (ESO) 2000

Online publication: December 11, 2000
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