Astron. Astrophys. 335, 985-990 (1998)

5. Kinematics

Using the derived physical parameters and the photometric data by Wesemael et al. (1992) together with theoretical fluxes and colours from Kurucz (1992) and an assumed mass of 0.55  we can estimate the distances of the two stars. The results are listed in Table 5. The error of 23% in distance is dominated by the error in (Moehler et al., 1990b), which we estimate to be 0.15 dex. Thejll et al. (1997) also measured proper motions for both stars, which we use to derive galactocentric velocities according to Johnson & Soderblom (1987). We used 8 kpc for the galactocentric distance of the Sun, (10, 15, 8) [km/s] for (, , ) and 225 km/s for the galactic rotation velocity at the place of the Sun. We also derived the velocities of PG 1704+222 along the axis pointing from the galactic center to its current position (within the galactic plane, ) and along the galactic rotation at its place (). From the value of we note that PG 1704+222 does not participate in the galactic rotation. The error of the proper motion of PG 1323-086 is so large that the resulting space velocity is inconclusive and therefore not listed in Table 5.

Table 5. Kinematic data for the two programme stars. U points from the sun to the galactic center, V towards l = 90, b = 0, W towards the galactic north pole. and are defined to point from the galactic center to the star (within the galactic plane) and along the galactic rotation at the place of the star, respectively.

Using the abundances derived from the same lines in the spectrum of HR 6588 we determined abundances relative to HR 6588 on a line by line basis. Most notably the abundances derived from Si II and Si III lines in PG 1323-086 and HR 6588 disagree by 0.43 dex and 1.05 dex, respectively, underlining the need for a differential abundance analysis.

Among the many abundance analyses of HR 6588 in the literature we choose the recent work by Hambly et al. (1997) to convert the relative abundances (averaged if possible) into absolute ones, since the authors used the same calibration of Strömgren colours to derive as we did. The results are listed in Table 3 and plotted in Fig. 4. The silicon abundance of PG 1323-086 as derived from Si II now agrees with that derived from the Si III lines. We adopt 0.3 dex as a typical error for all abundances.

Fig. 4. The abundances determined in this paper (filled symbols) compared to abundances of PAGB stars with similar abundance patterns (open triangles: PHL 174, PHL 1580, Conlon et al., 1991; open square: BD +332642 , Napiwotzki et al., 1994). The C abundances relying only on the C II 4267 Å line might be underestimated due to NLTE effects (Eber & Butler, 1988).

© European Southern Observatory (ESO) 1998

Online publication: June 26, 1998
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