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Astron. Astrophys. 318, 797-804 (1997)

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4. Application of the method

4.1. The samples

In order to apply the method, we searched the literature for high quality sets of observational data. We considered mainly two large and homogeneous sets of data: one from Moffett & Barnes (1980, 1984) (MB hereafter, BVRI photometry), Barnes et al. (1987, 1988) (BMS hereafter), Wilson et al. (1989) (WCBCM hereafter, radial velocities), and the other from Bersier et al. (1994) (BBB hereafter, Geneva System Photometry), Bersier et al. (1994) (BBMD hereafter, CORAVEL radial velocities).

There were 26 variables in common between the two sets; in these cases, in general, we used photometry from MB (we proceed in this way either because these data was generally more accurate than those in the Geneva system, or because the presence of the V-R color allowed us to use our modified CORS method) and radial velocity data from BBMD (since these set of data were much more accurate than the other one). For other three stars: SY Cas, SY Nor and TW Nor for which are present radial velocity data from BBMD, but no photometry in the Geneva System, we used photometric data from Berdnikov (1992a, b, c, B in Table 2) for the first two, and Madore (1975, M in Table 2) for the third. The incompleteness of photometric data for SY Nor did not allow us to determine the radius of this star.


Table 2. Results from our method and comparison with previous determinations with the Surface Brightness Method by Gieren et al. (1989). The last two columns show the radius calculated in this work.

4.2. Particular stars

There were eight stars from BMS and WCBCM whose radial velocities curves were too poor to be used, they are: FF Aql, RU Cam, RW Cas, TU Cas, SU Cyg, AU Peg, VX Pup, S Sge.

For other two stars of the same sample: RW Cam and VY Cyg, the method did not reach the convergence, probably due to the poor quality of the data.

SW Tau was excluded because it is a Population II Cepheid.

From the BBMD sample we excluded from our computation V440 Per, which have convergence problems; CO Aur and V367 Sct because they are double or triple mode; the double stars DL Cas and V465 Mon because of problems in separating the orbital motion from the radial velocity curve.

4.3. Double stars

From the literature is possible to find indications about the presence of a companion for several cepheids; in particular, following BBB, BBMD and Pont et al. (1994) the following variables result to be double: SU Cas, DD Cas, VZ Cyg, DX Gem, [FORMULA], RZ Gem, Z Lac, T Mon, S Nor, SV Per, Y Sct, U Sgr, W Sgr. Among these double stars, only U Sgr shows an anomaluos position in Fig. 4(see below).

[FIGURE] Fig. 4a and b. Top: Period-Radius relation obtained from CORS method without [FORMULA] ; Bottom: as before, but with [FORMULA].

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© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998