Periodicities in the high-mass X-ray binary system RX J0146.9+6121/LS I+61°235 |
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| Authors: | Gordon E Sarty László L Kiss Richard Huziak Lionel J J Catalan Diane Luciuk Timothy R Crawford David J Lane Roger D Pickard Thomas A Grzybowski Pere Closas Helen Johnston David Balam Kinwah Wu |
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| Institution: | Department of Physics and Engineering Physics, University of Saskatchewan, 9 Campus Drive, Saskatoon, Saskatchewan S7N 5A5, Canada;Institute of Astronomy, School of Physics A28, University of Sydney, New South Wales 2006, Australia;Lakehead University, 955 Oliver Rd., Thunder Bay, Ontario P7B 5E1, Canada;American Association of Variable Star Observers, 49 Bay State Rd., Cambridge, MA 02138, USA;Department of Astronomy and Physics, Saint Mary's University, 923 Robie St., Halifax, Nova Scotia B3H 3C3, Canada;Department of Physics and Astronomy, University of Victoria, PO Box 3055, STN CSC, Victoria, British Columbia V8W 3P6, Canada;Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT |
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| Abstract: | The high-mass X-ray binary RX J0146.9+6121, with optical counterpart LS I+61°235 (V831 Cas), is an intriguing system on the outskirts of the open cluster NGC 663. It contains the slowest Be type X-ray pulsar known with a pulse period of around 1400 s and, primarily from the study of variation in the emission line profile of Hα, it is known to have a Be decretion disc with a one-armed density wave period of approximately 1240 d. Here we present the results of an extensive photometric campaign, supplemented with optical spectroscopy, aimed at measuring short time-scale periodicities. We find three significant periodicities in the photometric data at, in order of statistical significance, 0.34, 0.67 and 0.10 d. We give arguments to support the interpretation that the 0.34 and 0.10 d periods could be due to stellar oscillations of the B-type primary star and that the 0.67 d period is the spin period of the Be star with a spin axis inclination of 23+10−8 degrees. We measured a systemic velocity of −37.0 ± 4.3 km s−1 confirming that LS I+61°235 has a high probability of membership in the young cluster NGC 663 from which the system's age can be estimated as 20–25 Myr. From archival RXTE All Sky Monitor (ASM) data we further find 'super' X-ray outbursts roughly every 450 d. If these super outbursts are caused by the alignment of the compact star with the one-armed decretion disc enhancement, then the orbital period is approximately 330 d. |
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| Keywords: | accretion accretion discs binaries: close stars: neutron |
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