12 HD 152178 = V2253 Oph

12.1 Brief history

HD 152178 was classified as G8/K0Vp and found to have CaII H and K emission by Houk (1982). However, our spectra indicate that the star is a K0 III (Strassmeier et al. 1993), a result consistent with its M_V determined from its Hipparcos parallax (ESA 1997). Hooten & Hall (1990) found a photometric period of 22.35 days. Our preliminary orbital elements were listed in the second edition of the CABS catalog (Strassmeier et al. 1993). The orbital period of 314.5 days is much longer than the rotational period, making the star an asynchronous rotator.

12.2 Orbital elements

Between 1986 and 1996 FCF obtained 32 observations at KPNO. The Vienna group made an additional 6 observations during an observing run in May 1996 at ESO plus a single observation at KPNO in 1998.

A preliminary orbital solution for the data of FCF was obtained with BISP, and those elements were refined with SB1. Then, the seven additional velocities were compared with this orbit. As a result, an orbital solution was computed with all 39 observations given unit weight, and no zero-point correction applied to any of the data. Because the eccentricity of that solution is quite small, $0.0236\pm 0.0091$, SB1C was used to compute a circular orbit with the full set of data. Following the precepts of Lucy & Sweeney (1971), the eccentric-orbit solution has been retained, and those orbital elements are listed in Table 5. Our radial velocities and velocity residuals to the computed orbit are listed in Table A13 in the Appendix. The computed orbit is compared to the observed velocities in Fig. 10. The standard error of an observation of unit weight is 0.6 kms^-1. A time of conjunction with the primary behind the secondary is HJD $2\,448\,226.377$.

 

Figure 10: Radial-velocity curve of HD 152178. Data obtained at KPNO and ESO are shown as filled and open circles, respectively, and were given equal weight

HD 152178 is clearly an asynchronous rotator and an interesting system but we note that the long orbital period suggests only weak tidal forces to synchronize the rotation.