The Orbits Of Subdwarf-B Plus Main-Sequence Binaries Iii. The Period-Eccentricity Distribution

The predicted orbital-period distribution of the subdwarf-B (sdB) population\nis bi-modal with a peak at short (< 10 days) and long (> 500 days) periods.\nObservationally, many short-period sdB systems are known, but only few wide sdB\nbinaries have been studied in detail. Based on a long-term monitoring program\nthe wide sdB sample has been increased, finding an unexpected correlation\nbetween the eccentricity and period. In this article we present the orbital\nsolution and spectral analysis of four new systems, BD-7.5977, EC11031-1348,\nTYC2084-448-1 and TYC3871-835-1, and update the orbital solution of PG1104+243.\nUsing the whole sample of wide sdBs, we aim at finding possible correlations\nbetween orbital and spectral properties, with as goal improving theoretical\nmodels of Roche-lobe overflow. High-resolution spectra were obtained to\ndetermine the radial velocities of both the sdB and MS components. Surface\ngravities and temperatures of both component were derived from photometric\nspectral-energy distributions. Spectral parameters of the cool companion were\nverified using the GSSP code. Furthermore the amount of accreted mass was\nestimated. Orbital parameters matching the earlier observed period-eccentricity\nrelation were found for three systems, while TYC 2084-448-1 is found to have a\nlower eccentricity than expected from the period-eccentricity trend indicated\nby the other systems. Based on new observations, the orbit of PG 1104+243 has a\nsmall but significant eccentricity of 0.04 $\\pm$ 0.02, matching other systems\nwith similar periods. Furthermore, a correlation between accreted mass and\norbital period was found, as well as a possible relation between the initial\nmass-ratio and the final period-eccentricity. The wide sdB-binary sample shows\ninteresting possible correlations between orbital and spectral properties.\nHowever, a larger sample is necessary to statistically validate them.\n