Brown Dwarf around dwarf nova U Geminorum?

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Brown Dwarf around dwarf nova U Geminorum?

Post by Edasich on 7th April 2009, 11:03 am

No full-paper. I quite dislike Springerlink. Suspect Mad

Orbital period analysis of eclipsing dwarf novae: U Geminorum

A new orbital period analysis for U Geminorum is made by means of the standard O–C technique based on 187 times of light minima including the three newest CCD data from our observation. Although there are large scatter near 70,000 cycles in its O–C diagram, there is strong evidence (>99.9% confidence level) to show the secular increase of orbital period with a rate dot{P}=7.8(1)× 10^{-12} s‑1. Using the physical parameters recently derived by Echevarría et al. (Astron. J. 134:262, 2007), the range of mass transfer rate for U Geminorum is estimated as from ‑3.5(5)×10‑9 M ȯ yr‑1 to ‑1.30(6)×10‑8 M ȯ yr‑1. Moreover, the data before 60,000 cycles shows the obvious quasi-period variations. The least square estimation of a ˜17.4 yr quasi-periodic variation superimposed on secular orbital period increase is derived. Considering the possibility that solar-type magnetic activity cycles in the secondary star of U Geminorum may produce the quasi-period variations of the orbital period, Applegate’s mechanism is discussed and the results indicate such mechanism has difficulty explaining the quasi-period variation for U Geminorum. Hence, we attempted to apply the light-travel time effect to interpret the quasi-period variation and found the perturbation of ˜17.4 yr quasi-period may result from a brown dwarf. If the orbital inclination is assumed as i˜15°, corresponding to the upper limit of mass of a brown dwarf, then its orbital radii is ˜7.7 AU.

Emphasis mine. Razz
dM star
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