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Astron. Astrophys. 324, 988-990 (1997)

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2. The data

The times of minima were collected by Chambliss (1972), Rovithis-Livaniou and Rovithis (1992) and by Chambliss (1993; photoelectric data only). Newer photoelectric minima were published by Rovithis-Livaniou & Rovithis (1994) and by Müyesseroglu et al. (1996). The photoelectric data are not numerous; they are presented in Fig. 2. In this graph, the ephemeris


(which resulted from first attempts to account for the light-time effect) is used. From eight photographic times published by Hoffmeister (1934) two mean minima are formed; the scatter of visual times is so large that they will not be considered here. One can see that the time of periastron had to occur at around JD 2437000 and that the orbital eccentricity is considerable.

[FIGURE] Fig. 1. [FORMULA] diagram for V 505 Sgr. Circles are photoelectric data for primary minima, crosses for secondary minima; asterisks are for photographic data. The curve corresponds to the light-time effect due to a third body with the orbit according to Table 2.
[FIGURE] Fig. 2. The visible relative orbit of the third body. The cross marks the position of the eclipsing pair, the plus signs correspond to data by McAlister et al. (1993; see Table 2), circles to calculated positions; the curve is calculated for the distance 102 pc. Scales on both axes are in arcsec, north is down, east to the right.

The speckle interferometry data by McAlister et al. (1993) are repeated in Table 1 and plotted in Table 2. It is apparent that these measurements were made after an apoastron passage.


Table 1. Interferometric data as given by McAlister et al. (1993)


Table 2. The parameters of the third body orbit

The radial velocity measurements as published by Tomkin (1991) are: [FORMULA] and [FORMULA] km/s for the primary and secondary component systemic velocities, for the tertiary component the velocity was -9 for JD 2444000 and -13 km/s for JD 2448000, with scatter of about 2 km/s. We will however show that data of higher accuracy would be needed for comparison with the expected values.

The formulae which describe the light-time effect (and the accompanied changes of radial velocities) are given e.g. by Mayer (1990) 1, formulae for the separation and position angle in the visual orbit are e.g. in Aitken (1935).

Combining the [FORMULA] behaviour (Fig. 2) and the speckle data (Fig. 2) it was possible to find parameters of the third body orbit as they are given in Table 2. This orbit satisfies also the photographic data; if the photographic data are not used in the solution, the resulting parameters differ only insignificantly. Since the secondary minimum times differ from the trend of the primary minima, the secondary minima are not considered. (From the two cases it is difficult to speculate if this difference is due to lower accuracy - the secondary minima are shallow - or due to orbital eccentricity. In an Algol system, zero eccentricity is of course expected.)

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© European Southern Observatory (ESO) 1997

Online publication: May 5, 1998