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

Autor: W. Skidmore, James N. Bleach, Edward L. Robinson, Janet H. Wood, M. S. Catalán, W. F. Welsh
Rok vydání: 2000
Předmět:
Zdroj: Monthly Notices of the Royal Astronomical Society. 312:70-82
ISSN: 1365-2966
0035-8711
Popis: We present spectra in the range 8000–8665 A of the close, detached M-dwarf–white-dwarf binaries EG UMa and PG 1026+002. The Na i absorption doublet (8183, 8195 A) 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 A). 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.
Databáze: OpenAIRE
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