Astrophysics and Space Science

, Volume 346, Issue 2, pp 463–475 | Cite as

Discovery of a coherent oscillation with a 1.07 h period in the suspected cataclysmic variable FBS 1220+753 (Dra 7)

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Abstract

We report results of extensive photometry of the suspected cataclysmic variable FBS 1220+753. The observations were obtained over 28 nights in 2010, 2011 and 2012. The total duration of the observations was 160 h. We clearly detected the highly coherent oscillation with a period of 1.0712887±0.0000013 h and a stable semi-amplitude of 0.03 mag. In a time scale of years, the oscillation period is very stable (dP/dt<(4.1±1.4)×10−10). The light curves of FBS 1220+753 show no obvious flickering. The significant brightness changes on large time intervals are also absent. Therefore, it is unlikely that FBS 1220+753 is a cataclysmic variable. The period is compatible with oscillations seen in δ Sct variables. But its high stability and the unchangeable oscillation amplitude suggest that the oscillation cannot be caused by multiperiodic stellar pulsations. The average pulse shape of the oscillation is very sinusoidal with slightly sharper maxima compared with minima, but it is somewhat changeable from year to year. The light curves obtained in 2011 and folded with the doubled oscillation period reveal that the adjacent oscillation cycles have slightly different depths of the minima and different steepness of the rise and decline. This behaviour resembles the behaviour of the binary subdwarf–white dwarf systems, in which the variability is caused by ellipsoidal variations. However, the folded light curve obtained from the data of 2010 reveal nearly equal shapes of the adjacent oscillation cycles, and this does not conform to such an interpretation. Thus, the nature of the oscillation seen in FBS 1220+753 remains puzzling. To solve this puzzle, detailed spectroscopic observations are needed.

Keywords

Stars: individual: FBS 1220+753 Novae, cataclysmic variables Subdwarfs Stars: variables: δ Scuti Stars: oscillations 
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Notes

Acknowledgements

This work was partly supported by the Federal Goal-Oriented Program “Researches and elaborations on priority directions of development of a scientific-technological complex of Russia” (State contract 14.518.11. 7064). This work has made use of the Digitised First Byurakan Survey (DFBS), which is a joint project among the Byurakan Astrophysical Observatory (BAO, Armenia), “La Sapienza” Universita di Roma (Italy), and Cornell University (Ithaca, NY, USA).

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Copyright information

© Springer Science+Business Media Dordrecht 2013

Authors and Affiliations

  1. 1.Astronomical ObservatoryUral Federal UniversityEkaterinburgRussia

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