10 HD 136901 = UV CrB

10.1 Brief history

Heard (1956) discovered the velocity variability of HD 136901 from nine radial velocities obtained at David Dunlap Observatory. A hiatus of several decades ensued before interest in this star was revived with Bidelman's (1983) discovery of weak CaII H and K emission in an objective-prism spectrum of HD 136901. That result spurred additional spectroscopic and photometric analyses. Fekel et al. (1986) obtained a preliminary spectroscopic period of 18.68 days, nearly twice the photometric period of 9.63 days discovered by Boyd et al. (1984). Fekel et al. (1989) published a full set of orbital elements and discussed the properties of the system. Strassmeier et al. (1989) confirmed the suggestion of Fekel et al. (1986) that the light variations are mainly due to the ellipticity effect. Kaye et al. (1995) evaluated a number of seasons of photometry of HD 136901 and removed the ellipticity effect. The remaining residuals were analyzed and in seven of the 11 data sets showed a periodicity within a few percent of the orbital period. Those additional light variations are presumably due to starspots.

10.2 Orbital elements

The Vienna group obtained 18 new velocities, nine at NSO and nine at KPNO. Those velocities were combined with two other previously published data sets, those of Fekel et al. (1989) and Heard (1956). Because of different assumed standard-star velocities, the Fekel et al. (1989) velocities used in the present analysis differ slightly from the originally published values.

We first computed independent SB1 orbital solutions of the velocities of Fekel et al. (1989) and of the combined set of velocities of the Vienna group. A comparison of the two solutions resulted in no zero-point shift to any of the data sets and unit weight assigned to all velocities, except for one velocity given zero weight. With Heard's (1956) velocities given weights of 0.01 and adjusted by -4 kms^-1, an orbital solution of all the data was obtained. The period was fixed at that value, and an orbital solution with SB1 was obtained for the revised Fekel et al. (1989) velocities plus those of the Vienna-group. The eccentricity of the orbit, $0.045 \,\pm\, 0.011$, although reduced slightly from the value of $0.059\,\pm\, 0.014$ obtained by Fekel et al. (1989), is still assumed to be real, in accordance with the precepts of Lucy & Sweeney (1971). Table 5 lists this eccentric-orbit solution. The individual observations and velocity residuals are presented in Table A11 in the Appendix. The calculated velocity curve is compared with the observed velocities in Fig. 8.

 

Figure 8: Radial-velocity curve of HD 136901. Data were obtained at KPNO (dots) and NSO (open circles) and were given equal weight except one KPNO velocity at phase 0.16 that was given zero weight

The standard error of an observation of unit weight is 1.2 kms^-1, primarily the result of the very broad lines of this star. A time of conjunction with the primary behind the secondary is HJD $2\,447\,312.447$.