13 HD 208472 = V2075 Cyg

13.1 Brief history

HD 208472 was identified as a chromospherically active star by Bidelman (1991), who discovered its CaII H and K emission features. Henry et al. (1995) found photometric variations with a period of 22.54 days and determined a preliminary orbital period of 22.6 days, making this star a synchronous rotator. They concluded that the system is very active as evidenced by its large-amplitude V-band variations of 0$.\!\!^{\rm m}$36 and an H$\alpha$ line above the continuum.

13.2 Orbital elements

From 1992 through 1998, 47 velocities were obtained at KPNO, 43 by FCF and 4 by the Vienna group. An additional 51 velocities were gathered by the Vienna group at NSO during a single 1996-1997 observing run.

Because of the much longer timespan of the data, orbital elements for the KPNO velocities were computed first with BISP, and refined with SB1. Then, an orbital solution for the NSO velocities was obtained, assuming the period from the KPNO-velocity solution. From a comparison of the two solutions, each NSO velocity was assigned a weight of 0.15 relative to the KPNO velocities, and no zero-point velocity correction was made. An orbital solution with the appropriately weighted data resulted in $e=0.0058\pm0.0071$, and so a circular-orbit solution was computed with SB1C. According to the precepts of Lucy & Sweeney (1971), the circular orbit is clearly preferable, and those elements are given in Table 5. Since the eccentricity is zero, the time of periastron passage has been replaced by the time of maximum velocity. Figure 11 compares the computed orbit with the observed velocities, while our radial velocities and velocity residuals to the computed orbit are given in Table A14 in the Appendix. The standard error of an observation of unit weight is 0.6 kms^-1, quite good for such an active star.

 

Figure 11: Radial-velocity curve of HD 208472. Filled circles are data obtained at KPNO and open circles are data obtained at NSO. The latter had inferior spectral coverage compared to the KPNO data and were given a weight of 0.15