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تسجيل مستخدم جديدHubble Space Telescope FUV Spectra of the Post-Common-Envelope Hyades Binary V471 Tauri
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We have carried out an analysis of the HST STIS archival spectra of the magnetic white dwarf in the Hyades eclipsing-spectroscopic, post-common envelope binary V471 Tauri, time resolved on the orbit and on the X-ray rotational phase of the magnetic white dwarf. An HST STIS spectrum obtained during primary eclipse reveals a host of transition region/chromospheric emission features including N V (1238, 1242), Si IV (1393, 1402), C IV (1548, 1550) and He II (1640). The spectroscopic characteristics and emission line fluxes of the transition region/chromosphere of the very active, rapidly rotating, K2V component of V471 Tauri, are compared with the emission characteristics of fast rotating K dwarfs in young open clusters. We have detected a number of absorption features associated with metals accreted onto the photosphere of the magnetic white dwarf from which we derive radial velocities. All of the absorption features are modulated on the 555s rotation period of the white dwarf with maximum line strength at rotational phase 0.0 when the primary magnetic accretion region is facing the observer. The photospheric absorption features show no clear evidence of Zeeman splitting and no evidence of a correlation between their variations in strength and orbital phase. We report clear evidence of a secondary accretion pole. We derive C and Si abundances from the Si IV and C III features. All other absorption lines are either interstellar or associated with a region above the white dwarf and/or with coronal mass ejection events illuminated as they pass in front of the white dwarf.
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We have used the GHRS onboard the HST to obtain Lyman-alpha spectra of the hot white-dwarf (WD) component of the short-period eclipsing DA+dK2 pre-cataclysmic binary V471 Tauri, a member of the Hyades star cluster. Radial velocities of the WD, combin
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We present high speed photometry and high resolution spectroscopy of the eclipsing post common envelope binary QS Virginis (QS Vir). Our UVES spectra span multiple orbits over more than a year and reveal the presence of several large prominences pass
ing in front of both the M star and its white dwarf companion, allowing us to triangulate their positions. Despite showing small variations on a timescale of days, they persist for more than a year and may last decades. One large prominence extends almost three stellar radii from the M star. Roche tomography reveals that the M star is heavily spotted and that these spots are long-lived and in relatively fixed locations, preferentially found on the hemisphere facing the white dwarf. We also determine precise binary and physical parameters for the system. We find that the 14,220 +/- 350K white dwarf is relatively massive, 0.782 +/- 0.013Ms, and has a radius of 0.01068 +/- 0.00007Rs, consistent with evolutionary models. The tidally distorted M star has a mass of 0.382 +/- 0.006Ms and a radius of 0.381 +/- 0.003Rs, also consistent with evolutionary models. We find that the magnesium absorption line from the white dwarf is broader than expected. This could be due to rotation (implying a spin period of only ~700 seconds), or due to a weak (~100kG) magnetic field, we favour the latter interpretation. Since the M stars radius is still within its Roche lobe and there is no evidence that its over-inflated we conclude that QS Vir is most likely a pre-cataclysmic binary just about to become semi-detached.
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istics of the population of post-common-envelope binaries (PCEB). As the evolution of these binaries and their stellar components are relatively simple, this population can be directly used to constraint CE evolution. Methods. We use the binary population synthesis code SeBa to simulate the current-day population of PCEBs in the Galaxy. We incorporate the selection effects in our model that are inherent to the general PCEB population and that are specific to the SDSS survey, which enables a direct comparison for the first time between the synthetic and observed population of visible PCEBs. Results. We find that selection effects do not play a significant role on the period distribution of visible PCEBs. To explain the observed dearth of long-period systems, the {alpha}-CE efficiency of the main evolutionary channel must be low. In the main channel, the CE is initiated by a red giant as it fills its Roche lobe in a dynamically unstable way. Other evolutionary paths cannot be constrained more. Additionally our model reproduces well the observed space density, the fraction of visible PCEBs amongst white dwarf (WD)- main sequence (MS) binaries, and the WD mass versus MS mass distribution, but overestimates the fraction of PCEBs with helium WD companions.
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