SDSS unveils a population of intrinsically faint cataclysmic variables at the minimum orbital period |
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| Authors: | B T Gänsicke M Dillon J Southworth J R Thorstensen P Rodríguez-Gil A Aungwerojwit T R Marsh P Szkody S C C Barros J Casares D de Martino P J Groot P Hakala U Kolb S P Littlefair I G Martínez-Pais G Nelemans M R Schreiber |
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| Institution: | Department of Physics, University of Warwick, Coventry CV4 7AL;Department of Physics and Astronomy, Dartmouth College, 6127 Wilder Laboratory, Hanover, NH 03755-3528, USA;Isaac Newton Group of Telescopes, Apartado de correos 321, E-38700 Santa Cruz de la Palma, Tenerife, Spain;Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain;Department of Physics, Faculty of Science, Naresuan University, Phitsanulok, 65000, Thailand;Astronomy Department, University of Washington, Seattle, WA 98195, USA;INAF - Osservatorio di Capodimonte, Via Moiariello 16, 80131 Napoli, Italy;Department of Astrophysics, IMAPP, Radboud University Nijmegen, PO Box 9010, 6500 GL Nijmegen, the Netherlands;Tuorla Observatory, University of Turku, Vaisalantie 20, FIN-21500 Piikkio, Finland;Department of Physics and Astronomy, The Open University, Walton Hall, Milton Keynes MK7 6AA;Department of Physics and Astronomy, University of Sheffield, Sheffield, S3 7RH;Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain;Departamento de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso, Chile |
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| Abstract: | We discuss the properties of 137 cataclysmic variables (CVs) which are included in the Sloan Digital Sky Survey (SDSS) spectroscopic data base, and for which accurate orbital periods have been measured. 92 of these systems are new discoveries from SDSS and were followed-up in more detail over the past few years. 45 systems were previously identified as CVs because of the detection of optical outbursts and/or X-ray emission, and subsequently re-identified from the SDSS spectroscopy. The period distribution of the SDSS CVs differs dramatically from that of all the previously known CVs, in particular it contains a significant accumulation of systems in the orbital period range 80–86 min. We identify this feature as the elusive 'period minimum spike' predicted by CV population models, which resolves a long-standing discrepancy between compact binary evolution theory and observations. We show that this spike is almost entirely due to the large number of CVs with very low accretion activity identified by SDSS. The optical spectra of these systems are dominated by emission from the white dwarf photosphere, and display little or no spectroscopic signature from the donor stars, suggesting very low mass companion stars. We determine the average absolute magnitude of these low-luminosity CVs at the period minimum to be 〈 Mg 〉= 11.6 ± 0.7 . Comparison of the SDSS CV sample to the CVs found in the Hamburg Quasar Survey and the Palomar Green Survey suggests that the depth of SDSS is the key ingredient resulting in the discovery of a large number of intrinsically faint short-period systems. |
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| Keywords: | binaries: close stars: dwarf novae stars: evolution novae cataclysmic variables stars: statistics |
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