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Post Info TOPIC: V471 Tauri
Blobrana


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RE: V471 Tauri
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Title: The V471 Tauri System: A Multi-datatype Probe 
Author: Todd R. Vaccaro, Robert E. Wilson, Walter Van Hamme, Dirk Terrell 

V471 Tauri, a white dwarf--red dwarf eclipsing binary in the Hyades, is well known for stimulating development of common envelope theory, whereby novae and other cataclysmic variables form from much wider binaries by catastrophic orbit shrinkage. Our evaluation of a recent imaging search that reported negative results for a much postulated third body shows that the object could have escaped detection or may have actually been seen. The balance of evidence continues to favour a brown dwarf companion about 12 AU from the eclipsing binary. A recently developed algorithm finds unified solutions from three datatypes. New radial velocities (RVs) of the red dwarf and BV RCIC light curves are solved simultaneously along with white dwarf and red dwarf RVs from the literature, uvby data, the MOST mission light curve, and 40 years of eclipse timings. Precision-based weighting is the key to proper information balance among the various datasets. Timewise variation of modelled starspots allows unified solution of multiple data eras. Light curve amplitudes strongly suggest decreasing spottedness from 1976 to about 1980, followed by approximately constant spot coverage from 1981 to 2005. An explanation is proposed for lack of noticeable variation in 1981 light curves, in terms of competition between spot and tidal variations. Photometric spectroscopic distance is estimated. The red dwarf mass comes out larger than normal for a K2V star, and even larger than adopted in several structure and evolution papers. An identified cause for this result is that much improved red dwarf RVs curves now exist. 

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Blobrana


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HIP 17962
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Zooming in on the unusual binary star V471 Tauri 

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Blobrana


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Posts: 131433
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RE: V471 Tauri
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The Strange Case of the Missing Dwarf

The new SPHERE instrument on ESO's Very Large Telescope has been used to search for a brown dwarf expected to be orbiting the unusual double star V471 Tauri. SPHERE has given astronomers the best look so far at the surroundings of this intriguing object and they found - nothing. The surprising absence of this confidently predicted brown dwarf means that the conventional explanation for the odd behaviour of V471 Tauri is wrong. This unexpected result is described in the first science paper based on observations from SPHERE.
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Title: Hubble Space Telescope FUV Spectra of the Post-Common-Envelope Hyades Binary V471 Tauri
Authors: E. M. Sion, H. E. Bond, D. Lindler, P. Godon, D. Wickramasinghe, L. Ferrario, J. Dupuis

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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