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

Abstract

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, 8195 Å (31.2 ± 3.7 km s−1), the Fe and Ti intrinsically narrow metal (INM) lines in the region 8374–8430 Å (26.6 ± 2.7 and 27.8 ± 3.0 km s−1) and the K i line at 7698.9 Å (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, 8195 Å 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.

White Dwarf–Red Dwarf Systems Resolved with theHubble Space Telescope. I. First Results

“…Catalán et al (1995) added the possibility that the system is face-on or has low enough inclination to preclude significant variations in radial velocity as seen from Earth. Bleach et al (2002) conclude that the system is not face-on from a positive detection of rotational broadening (v rot sin i ¼ 25:2 AE 2:3 km s À1 ) in the red dwarf at several lines in a high-resolution optical spectrum. Given that all components of the triple system are seen in the ACS image, it is entirely possible that this system has a low inclination, and the line broadening reported by Bleach et al (2002) might be due in part or in whole to the binarity of the red dwarf component.…”

“…Bleach et al (2002) conclude that the system is not face-on from a positive detection of rotational broadening (v rot sin i ¼ 25:2 AE 2:3 km s À1 ) in the red dwarf at several lines in a high-resolution optical spectrum. Given that all components of the triple system are seen in the ACS image, it is entirely possible that this system has a low inclination, and the line broadening reported by Bleach et al (2002) might be due in part or in whole to the binarity of the red dwarf component. Somewhat surprisingly, Morales-Rueda et al (2005) list this system among all known detached, post-common-envelope binaries with known periods, Tables 3 and 4 for which the ACS imaging data were sensitive to companion detection in the 0.3 AU (the minimum detectable projected separation) to 10 AU range.…”

Echelle observations of chromospheric activity in post-common-envelope binaries

“…An alternative configuration for the binary system was discussed by Catalán et al (1995), who also observed changes in emission‐line strength, in which RE J1629+780 is a very low‐inclination system and does not necessarily have to be a long‐period binary. However, the measurement of rotational broadening in the secondary star of RE J1629+780 by Bleach et al (2002) suggests that we are not observing this system pole‐on.…”

“…For wavelength regions/echelle orders that contained white dwarf spectral features it was necessary to incorporate into the subtraction the radial velocity shift caused by the orbit of the white dwarf around the centre of mass of the binary system. To do this a white dwarf radial velocity curve was produced using data from Stauffer (1987) phased on to the updated ephemeris of Bleach et al (2002). The radial velocity shifts calculated were applied to the suitably scaled white dwarf models before their subtraction from the observed spectra.…”

“…The upper spectrum is of the M‐star Gl 699 which has a spectral type of M4V/M5V, as measured by Reid, Hawley & Gizis (1995) , and Gliese & Jahreiss (1991) , respectively, and is therefore similar in spectral type to the secondary star in EG UMa. The Gl 699 spectrum has been rotationally broadened by 28 km s −1 (limb darkening = 0.5) to represent the EG UMa secondary star V rot sin i (from Bleach et al 2002 ). Infilling of the Ca ii IRT absorption caused by the active chromosphere in the secondary star in EG UMa is clearly visible.…”