Observations of the post-common-envelope binaries EG UMa and PG 1026+002

Abstract

We present spectra in the range 8000–8665 Å of the close, detached M‐dwarf–white‐dwarf binaries EG UMa and PG 1026+002. The Na i absorption doublet (8183, 8195 Å) is detected along with a number of other absorption lines including intrinsically narrow metal Fe i and Ti i lines and the Ca ii infrared (IR) triplet (8498, 8542, 8662 Å). We update the ephemeris and orbital period of EG UMa. The radial velocity semi‐amplitude for the secondary star in EG UMa was found to be 125.9±0.4 km s−1. The excellent agreement between this value and that measured from emission lines, in conjunction with the lack of orbital‐phase variation of the absorption line strengths, confirms that the secondary‐star emission in EG UMa is chromospheric in nature and not influenced by irradiation. We determine a range of rotational velocities, Vrot sin i, for EG UMa as measured over the Na i absorption doublet and the Fe i and Ti i metal lines using three template stars. Although a broad range of Vrot sin i values are obtained, the narrow metal lines were found to give consistantly lower values than that given by the Na i absorption doublet. In addition, the measured values of Vrot sin i were inconsistent with other measured parameters and were therefore deemed too unreliable to be the basis for full system parameter calculations. We do, however, derive a complete set of system parameters for EG UMa based upon our new measurement of K2 and previous observational data. We present R‐band relative photometry of EG UMa, which shows relative flux variations at around the 5 per cent level and the occurrence of a flare event. These observations are again interpreted as being the result of the intrinsic chromospheric activity of the M dwarf in this system. We measure the semi‐amplitude of the radial‐velocity curve for PG 1026+002 to be 163.7±7.3 km s−1, which, being in agreement with that measured from emission lines, adds further support to the suggestion that the secondary‐star emission in PG 1026+002 is also largely chromospheric in nature. Rotational velocities for PG 1026+002 were determined by measurement over the Na i absorption doublet only. The Vrot sin i values obtained for PG 1026+002 using the three available template stars were all greater than expected from the assumption of synchronous rotation.

The age, life expectancy, and space density of Post Common Envelope Binaries

“…% Radii of the secondary calculated by using the mass-radius relation given by Politano (1996). References: (1) Bruch (1999), (2) Bragaglia et al (1995), (3) Bleach et al (2000), (4) Kawka et al (2002), (5) Marsh & Duck (1996), (6) Maxted et al (1998), (7) Saffer et al (1993), (8) Kepler & Nelan (1993), (9) Kawka et al (2000), (10) Koester et al (1979), (11) Stauffer (1987), (12) Lanning & Pesch (1981), (13) Guinan & Sion (1984), (14) Schmidt et al (1995), (15) Wood & Saffer (1999), (16) Drechsel et al (2001), (17) Orosz et al (1999), (18) Maxted et al (2002), (19) O'Brien et al (2001), (20) Kilkenny et al (1998), (21) Rauch (2000), (22) Vennes et al (1999), (23) …”

“…EG UMa: Discovered as a white dwarf on Schmidt prism plates by Stephenson (1960), emission lines noted by Greenstein (1965), orbital period (spectroscopic) by Lanning (1982). Recent comprehensive study by Bleach et al (2000).…”

Roche tomography of cataclysmic variables - II. Images of the secondary stars in AM Her, QQ Vul, IP Peg and HU Aqr

“…Ideally, this should be the same line taken from the spectrum of a slowly rotating star of the same spectral class as the star being mapped, preferably obtained with the same instrumental set‐up. Unfortunately, only one of the spectral‐type template stars that were observed is useful (GL806 – see Table 2); the others show signs of broadening of the Na i doublet and have been identified as either flare stars, and are therefore probably rapidly rotating, or binary stars, where V rot sin i measurements using the Na i absorption doublet have been found to be systematically greater than those given by the narrow metal lines (Bleach et al 2000). We used the GL806 template in all of our reconstructions and, even though the spectral class of the template differs from those of the stars being mapped, the exact shape of the template profile used has little effect on the reconstructions, owing to the large degree of rotational broadening present in CV secondary stars.…”

HS 2237+8154: On the onset of mass transfer or entering the period gap?

“…Narrow emission of Hα and Hβ is detected, which is most likely associated with chromospheric activity on the late-type companion (e.g. Bleach et al 2000).…”