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SW Sextantis stars: the dominant population of cataclysmic variables with orbital periods between 3 and 4 h

Rodríguez-Gil, P. and Gänsicke, B. T and Hagen, H.-J. and Araujo-Betancor, S. and Aungwerojwit, A. and Allende Prieto, C. and Boyd, D. and Casares, J. and Engels, D. and Giannakis, O. and Harlaftis, E. T. and Kube, J. and Lehto, H. and Martínez-Pais, I. G. and Schwarz, R. and Skidmore, W. and Staude, A. and Torres, M. A. P. (2007) SW Sextantis stars: the dominant population of cataclysmic variables with orbital periods between 3 and 4 h. Monthly Notices of the Royal Astronomical Society, 377 (4). pp. 1747-1762. ISSN 0035-8711.

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We present time-series optical photometry of five new cataclysmic variables (CVs) identified by the Hamburg Quasar Survey (HQS). The deep eclipses observed in HS 0129+2933 (= TT Tri), HS 0220+0603 and HS 0455+8315 provided very accurate orbital periods of 3.35129827(65), 3.58098501(34) and 3.56937674(26) h, respectively. HS 0805+3822 shows grazing eclipses and has a likely orbital period of 3.2169(2) h. Time-resolved optical spectroscopy of the new CVs (with the exception of HS 0805+3822) is also presented. Radial velocity studies of the Balmer emission lines provided an orbital period of 3.55 h for HS 1813+6122, which allowed us to identify the observed photometric signal at 3.39 h as a negative superhump wave. The spectroscopic behaviour exhibited by all the systems clearly identifies them as new SW Sextantis (SW Sex) stars. HS 0220+0603 shows unusual N ii and Si ii emission lines suggesting that the donor star may have experienced nuclear evolution via the CNO cycle. These five new additions to the class increase the number of known SW Sex stars to 35. Almost 40 per cent of the total SW Sex population do not show eclipses, invalidating the requirement of eclipses as a defining characteristic of the class and the models based on a high orbital inclination geometry alone. On the other hand, as more SW Sex stars are identified, the predominance of orbital periods in the narrow 3–4.5 h range is becoming more pronounced. In fact, almost half the CVs which populate the 3–4.5 h period interval are definite members of the class. The dominance of SW Sex stars is even stronger in the 2–3 h period gap, where they make up 55 per cent of all known gap CVs. These statistics are confirmed by our results from the HQS CVs. Remarkably, 54 per cent of the Hamburg nova-like variables have been identified as SW Sex stars with orbital periods in the 3–4.5 h range. The observation of this pile-up of systems close to the upper boundary of the period gap is difficult to reconcile with the standard theory of CV evolution, as the SW Sex stars are believed to have the highest mass-transfer rates among CVs. Finally, we review the full range of common properties that the SW Sex stars exhibit. Only a comprehensive study of this rich phenomenology will prompt to a full understanding of the phenomenon and its impact on the evolution of CVs and the accretion processes in compact binaries in general.

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Additional Information:© 2007 The Authors. Journal compilation © 2007 RAS. Accepted 2007 March 15. Received 2007 March 8; in original form 2007 February 9. In the memory of Emilios Harlaftis. AA thanks the Royal Thai Government for a studentship. BTG was supported by a PPARC Advanced Fellowship. MAPT is supported by NASA LTSA grant NAG-5-10889. RS is supported by the Deutsches Zentrum f¨ur Luft und Raumfahrt (DLR) GmbH under contract No. FKZ 50 OR 0404. AS is supported by the Deutsche Forschungsgemeinschaft through grant Schw536/20-1. The HQS was supported by the Deutsche Forschungsgemeinschaft through grants Re 353/11 and Re 353/22. This paper includes data taken at The McDonald Observatory of The University of Texas at Austin. It is also based in part on observations obtained at the German-Spanish Astronomical Center, Calar Alto, operated by the Max-Planck-Institut f¨ur Astronomie, Heidelberg, jointly with the Spanish National Commission for Astronomy, on observations made at the 1.2-m telescope, located at KryoneriKorinthias, and owned by the National Observatory of Athens, Greece, on observations made with the Isaac Newton Telescope, which is operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrof´ısica de Canarias (IAC), on observations made with the 1.2-m telescope at the Fred Lawrence Whipple Observatory, a facility of the Smithsonian Institution, on observations made with the IAC80 telescope, operated on the island of Tenerife by the IAC in the Spanish Observatorio del Teide, on observations made with the OGS telescope, operated on the island of Tenerife by the European Space Agency, in the Spanish Observatorio del Teide of the IAC, and on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the IAC, and on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. This publication makes use of data products from 2MASS, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.
Funding AgencyGrant Number
Royal Thai GovernmentUNSPECIFIED
Particle Physics and Astronomy Research Council (PPARC) Advanced FellowshipUNSPECIFIED
Deutsches Zentrum für Luft und Raumfahrt (DLR) GmbHFKZ 50 OR 0404
Deutsche ForschungsgemeinschaftSchw536/20-1
Deutsche ForschungsgemeinschaftRe 353/11
Deutsche ForschungsgemeinschaftRe 353/22
Subject Keywords:accretion, accretion discs; binaries: close; novae, cataclysmic variables
Issue or Number:4
Record Number:CaltechAUTHORS:20100311-114008360
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:17725
Deposited By: Jason Perez
Deposited On:11 Mar 2010 21:12
Last Modified:03 Oct 2019 01:32

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