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Astron. Astrophys. 318, 783-790 (1997)

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2. Observational data

The first detection of the binary NTTS 162814-2427 was made by Montmerle et al. (1983) in the X-ray wavelength band using the Einstein satellite. The binary, situated among the naked T Tauri population of the Scorpius Ophiuchus star-forming region, was later observed by MWM who obtained the corresponding orbital solution. From that orbital solution MWM derived a period of 35.95  [FORMULA]  0.02 days and an eccentricity of 0.48  [FORMULA]  0.01. They also obtained an estimate for the dynamical mass ratio of 1.09  [FORMULA]  0.07 as well as a lower limit for the primary mass of [FORMULA] and for the secondary mass of [FORMULA]. Adopting a single extinction value for both components, [FORMULA], they estimated the primary luminosity to be [FORMULA] and suggested this binary is composed of a K7 primary and a late-K secondary.

A more sophisticated study of the NTTS 162814-2427 binary was made by Lee (1992) using high-dispersion optical spectroscopy, low-dispersion spectrophotometry and broadband photometry, to investigate the characteristics of its components. The study suggests this binary is composed of K4 and K5 stars, allowing thus four possible primary-secondary spectral type combinations. For each of these combinations Lee derived the primary and secondary luminosities from the observed flux ratios. This was done using two different values for the parameter characterising the extinction law, [FORMULA], namely 3.1 and 5.0. The first corresponds to the value typically found in the diffuse interstellar medium, while the second was obtained by Lee fitting extinction curves to his photometric results. We note that values of [FORMULA] greater than four have also been reported by Cardelli (1988) for stars in the Ophiuchus molecular cloud. On the other hand, Bouvier & Appenzeller (1991) obtained [FORMULA] for the NTTS 162814-2427 binary. This value is in better agreement with the one derived by Lee using [FORMULA] [FORMULA] rather than [FORMULA] [FORMULA]. Therefore we adopt [FORMULA] in this work. Table 1 summarises the observational data available for the binary NTTS 162814-2427 relevant for this study.


Table 1. Observational data for the binary NTTS 162814-2427 (Lee 1992). Effective temperatures were derived using the Cohen & Kuhi (1979) spectral type-effective temperature scale. Luminosities correspond to [FORMULA]. Estimated errors are [FORMULA] and [FORMULA] (details in Sect. 5)

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© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998