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Enigmatic Recurrent Pulsational Variability of the Accreting White Dwarf EQ Lyn (SDSS J074531.92+453829.6)

Mukadam, Anjum S. and Townsley, D. M. and Szkody, Paula and Gänsicke, B. T. and Southworth, J. and Brockett, T. and Parsons, S. and Hermes, J. J. and Montgomery, M. H. and Winget, D. E. and Harrold, S. and Tovmassian, G. and Zharikov, S. and Drake, A. J. and Henden, A. and Rodríguez-Gil, P. and Sion, E. M. and Zola, S. and Szymanski, T and Pavlenko, E. and Aungwerojwit, A. and Qian, S.-B. (2013) Enigmatic Recurrent Pulsational Variability of the Accreting White Dwarf EQ Lyn (SDSS J074531.92+453829.6). Astronomical Journal, 146 (3). Art. No. 54. ISSN 0004-6256. http://resolver.caltech.edu/CaltechAUTHORS:20130923-142836799

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Abstract

Photometric observations of the cataclysmic variable EQ Lyn (SDSS J074531.92+453829.6), acquired from 2005 October to 2006 January, revealed high-amplitude variability in the range 1166–1290 s. This accreting white dwarf underwent an outburst in 2006 October, during which its brightness increased by at least five magnitudes, and it started exhibiting superhumps in its light curve. Upon cooling to quiescence, the superhumps disappeared and it displayed the same periods in 2010 February as prior to the outburst within the uncertainties of a couple of seconds. This behavior suggests that the observed variability is likely due to nonradial pulsations in the white dwarf star, whose core structure has not been significantly affected by the outburst. The enigmatic observations begin with an absence of pulsational variability during a multi-site campaign conducted in 2011 January–February without any evidence of a new outburst; the light curve is instead dominated by superhumps with periods in the range of 83–87 minutes. Ultraviolet Hubble Space Telescope time-series spectroscopy acquired in 2011 March reveals an effective temperature of 15,400 K, placing EQ Lyn within the broad instability strip of 10,500–16,000 K for accreting pulsators. The ultraviolet light curve with 90% flux from the white dwarf shows no evidence of any pulsations. Optical photometry acquired during 2011 and Spring 2012 continues to reflect the presence of superhumps and an absence of pulsations. Subsequent observations acquired in 2012 December and 2013 January finally indicate the disappearance of superhumps and the return of pulsational variability with similar periods as previous data. However, our most recent data from 2013 March to May reveal superhumps yet again with no sign of pulsations. We speculate that this enigmatic post-outburst behavior of the frequent disappearance of pulsational variability in EQ Lyn is caused either by heating the white dwarf beyond the instability strip due to an elevated accretion rate, disrupting pulsations associated with the He ii instability strip by lowering the He abundance of the convection zone, free geometric precession of the entire system, or appearing and disappearing disk pulsations.


Item Type:Article
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http://dx.doi.org/10.1088/0004-6256/146/3/54DOIArticle
http://iopscience.iop.org/1538-3881/146/3/54/articlePublisherArticle
Additional Information:© 2013 American Astronomical Society. Received 2013 March 9; accepted 2013 June 17; published 2013 August 2. and either rule out or confirm the hypotheses presented here. We thank Dr. S. O. Kepler and Dr. E. L. Robinson for intriguing and helpful conversations during the writing of this paper. A.S.M. and P.S. acknowledge the NSF for the grant AST-1008734 which provided funding for this project. Support for the program HST-GO-12231.01-A was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. J.J.H.,M.H.M., and D.E.W. acknowledge support from the NSF under grant AST-0909107 and the Norman Hackerman Advanced Research Program under grant 003658-0252-2009, and M.H.M. additionally acknowledges the support of NASA under grant NNX12AC96G and the Delaware Asteroseismic Research Center. This research is based on data from the CRTS survey, which is supported by the NSF under the grant AST-0909182. The CSS survey is funded by NASA under the grant NNG05GF22G issued through the Science Mission Directorate Near-Earth Objects Observations Program. We thank the Las Cumbres Observatory for time on the 2 m FTN.
Funders:
Funding AgencyGrant Number
NSFAST- 1008734
NASAHST-GO-12231.01-A
Space Telescope Science InstituteUNSPECIFIED
NSFAST-0909107
Norman Hackerman Advanced Research Program003658-0252-2009
NASANNX12AC96G
Delaware Asteroseismic Research CenterUNSPECIFIED
NSFAST-0909182
NASANNG05GF22G
Science Mission Directorate Near-Earth Objects Observations ProgramUNSPECIFIED
Subject Keywords:novae, cataclysmic variables; stars: dwarf novae; stars: individual (EQ Lyn, SDSSJ074531.92+453829.6); stars: oscillations; stars: variables: general; white dwarfs
Record Number:CaltechAUTHORS:20130923-142836799
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20130923-142836799
Official Citation:Enigmatic Recurrent Pulsational Variability of the Accreting White Dwarf EQ Lyn (SDSS J074531.92+453829.6) Anjum S. Mukadam et al. 2013 The Astronomical Journal 146 54
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:41484
Collection:CaltechAUTHORS
Deposited By: Jason Perez
Deposited On:24 Sep 2013 20:10
Last Modified:24 Sep 2013 20:10

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