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Astron. Astrophys. 361, L49-L52 (2000)

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3. Orbital and fundamental stellar parameters

Fig. 1 shows the photometric light-curves in the B and V bands, and the radial velocity curves for RXJ 0529.4+0041 folded in phase. The orbital period, originally derived from the study of radial velocity data alone, has now been refined from the analysis of the photometric curves. The eclipses, lasting just a few hours, remained unnoticed until November 1999.

[FIGURE] Fig. 1. Upper panels : phase-folded B and V light-curves; lower panel : radial velocity curves for RXJ0529.4+0041 (filled circles and solid line refer to the primary component, open circles and the dotted line to the secondary; the horizontal dashed line indicates the systemic radial velocity, [FORMULA])

The light-curve solution presented here is obtained using the program Nightfall  1 As a starting point, all the information derived from the spectroscopy (e.g., mass ratio, minimum masses, projected semi-major axes, and spectral types) have been used to evaluate unknown parameters (namely, the orbital inclination and fractional radii of the stars), to a first approximation. The spectral types of K1-K2 and K7-M0 for the binary components have been estimated by matching the spectra of RXJ0529.4+0041 with `synthetic binary' spectra, obtained by different combinations of standard stars of known spectral type. For a first determination of the effective temperatures, the spectral type-temperature calibration from de Jager & Nieuwenhuijzen (1987) has been used. Given the proximity of the two components, the reflection effect has also been considered, as well as the presence of a third light, due to the close visual companion. A number of iterations have been performed using the result of the last best-fit as a starting point, and by allowing only up to four parameters to vary simultaneously (namely, the orbital inclination, the fractional radii of the components, and the effective temperature of the secondary).

The resulting orbital and stellar parameters are reported in Table 1. The orbital plane inclination is found to be nearly 87o thus not sufficient, given the separation and sizes of the two components, for producing a total eclipse, although about 90% of the secondary disc is occulted at the secondary minimum. In order to have a more realistic evaluation of the errors on the derived parameters, we have performed a grid of trial solutions adopting extreme values of the effective temperature of the primary component, accounting for the uncertainty on spectral type (one subclass) as well as for uncertainties in the temperature calibration.


[TABLE]

Table 1. Orbital and stellar parameters


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© European Southern Observatory (ESO) 2000

Online publication: October 10, 2000
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