Circumbinary planets around DV UMa and EX Dra?

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Circumbinary planets around DV UMa and EX Dra?

Post by Edasich on 1st June 2017, 3:57 am

Two almost unnoticed announcements, though not (yet) solid detections seemingly.

Cyclic period oscillation of the eclipsing dwarf nova DV UMa

DV UMa is an eclipsing dwarf nova with an orbital period of ∼2.06 h, which lies just at the bottom edge of the period gap. To detect its orbital period changes we present 12 new mid-eclipse times by using our CCD photometric data and archival data. Combining with the published mid-eclipse times in quiescence, spanning ∼30 yr, the latest version of the O−C diagram was obtained and analyzed. The best fit to those available eclipse timings shows that the orbital period of DV UMa is undergoing a cyclic oscillation with a period of 17.58(0.52) yr and an amplitude of 71.1(6.7) s. The periodic variation most likely arises from the light-travel-time effect via the presence of a circumbinary object because the required energy to drive the Applegate mechanism is too high in this system. The mass of the unseen companion was derived as M3sini′=0.025(0.004)M⊙. If the third body is in the orbital plane (i.e. i′=i=82.9∘) of the eclipsing pair, it would match to a brown dwarf. This hypothetical brown dwarf is orbiting its host star at a separation of ∼8.6 AU in an eccentric orbit (e=0.44).


Double cyclic variations in orbital period of the eclipsing cataclysmic variable EX Dra

EX Dra is a long-period eclipsing dwarf nova with ∼2−3 mag amplitude outbursts. This star has been monitored photometrically from November, 2009 to March, 2016 and 29 new mid-eclipse times were obtained. By using new data together with the published data, the best fit to the O−C curve indicate that the orbital period of EX Dra have an upward parabolic change while undergoing double-cyclic variations with the periods of 21.4 and 3.99 years, respectively. The upward parabolic change reveals a long-term increase at a rate of P˙=+7.4610−11ss−1. The evolutionary theory of cataclysmic variables (CVs) predicts that, as a CV evolves, the orbital period should be decreasing rather than increasing. Secular increase can be explained as the mass transfer between the secondary and primary or may be just an observed part of a longer cyclic change. Most plausible explanation for the double-cyclic variations is a pair of light travel-time effect via the presence of two companions. Their masses are determined to be MAsini′A=29.3(0.6)MJup and MBsini′B=50.8(0.2)MJup. When the two companions are coplanar to the orbital plane of the central eclipsing pair, their masses would match to brown dwarfs.

Plus a possible re-post:

Long-term Decrease and Cyclic Variation in the Orbital Period of the Eclipsing Dwarf Nova V2051 Oph

V2051 Oph is a deeply eclipsing dwarf nova with an orbital period below the period gap of cataclysmic variables (CVs). It has been photometrically monitored since 2008 June and 24 mid-eclipse times of the white dwarf have been obtained. The changes in the orbital period are investigated using all of the available mid-eclipse times. A continuous period decrease with a rate of \dot{P}=-5.93 {10}-10 {days} {{yr}}-1 was discovered to be superimposed on a periodic variation with a small amplitude of 0.ͩ000329 and a period of 21.64 years. The standard theory predicted that the evolution of CVs below the period gap is driven by gravitational radiation. However, angular momentum loss (AML) via gravitational radiation is insufficient to explain this decrease, and additional AML via magnetic braking that is about five times the gravitational radiation rate is required. This is consistent with the theoretical requirement indicating that magnetic braking of the fully convective star is not completely stopped. The cyclic oscillation was interpreted as the variation of the arriving eclipse time via the presence of a third body because the required energy for the Applegate mechanism is much larger than that radiated from the secondary in 10 years. Its mass is derived as {M}3{sin}{i}\prime =7.3(+/- 0.7) Jupiter mass. For orbital inclinations {i}\prime ≥slant 30\buildrel{\circ}\over{.} 3, it would be a planetary object. The giant circumbinary planet is orbiting around V2051 Oph at an orbital separation of about 9.0 astronomical units (AU) in an eccentric orbit (e‧ = 0.37). These conclusions support the ideas that some planets could survive stellar late evolution and that dwarf novae are also planetary hosting stars.
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