The measurement of rotational broadening in post-common-envelope binaries

We employ high-resolution echelle spectroscopy to measure the projected rotational velocity, Vrot sin i, in the post-common-envelope binaries EG UMa, HZ 9 and RE J1629 + 780. For EG UMa we obtain consistent Vrot sin i measurements from the Na i doublet at 8183, 8195Å (31.2 ± 3.7 km s−1), the Fe and Ti intrinsically narrow metal (INM) lines in the region 8374–8430Å (26.6 ± 2.7 and 27.8 ± 3.0 km s−1) and the K i line at 7698.9Å (26.2 ± 3.5 km s−1). This is in contrast to previous measurements of Vrot sin i from the Na i doublet and INM features derived using lower-resolution spectra, which were not consistent. Possible origins for the disagreement observed previously are discussed, including the inaccurate removal of telluric absorption. The values of Vrot sin i measured from the high-resolution EG UMa spectra are also consistent with that expected from system parameters derived from previous observational data. We also update the ephemeris and orbital period of EG UMa. We obtained rotation rate measurements of 34.3 ± 3.8 km s−1 for HZ 9 and 25.1 ± 2.3 km s−1 for RE J 1629 + 780, as measured from the Na i doublet at 8183, 8195Å and the INM lines. In both systems there is agreement between the Vrot sin i values measured from the two regions. The value of Vrot sin i measured in HZ 9 is similar to that measured for EG UMa. This is expected, as these systems share a similar orbital period and secondary star spectral type. The measurement of Vrot sin i in RE J 1629 + 780 indicates that this system, which lacks radial velocity shifts due to orbital motion, is a wide binary as opposed to a low-inclination system.