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تسجيل مستخدم جديدDetection limits for close eclipsing and transiting sub-stellar and planetary companions to white dwarfs in the WASP survey
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F. Faedi
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We used photometric data from the WASP (Wide-Angle Search for Planets) survey to explore the possibility of detecting eclipses and transit signals of brown dwarfs, gas giants and terrestrial companions in close orbit around white dwarfs. We performed extensive Monte Carlo simulations and we found that for Gaussian random noise WASP is sensitive to companions as small as the Moon orbiting a $Vsim$12 white dwarf. For fainter stars WASP is sensitive to increasingly larger bodies. Our sensitivity drops in the presence of co-variant noise structure in the data, nevertheless Earth-size bodies remain readily detectable in relatively low S/N data. We searched for eclipses and transit signals in a sample of 194 white dwarfs in the WASP archive however, no evidence for companions was found. We used our results to place tentative upper limits to the frequency of such systems. While we can only place weak limits on the likely frequency of Earth-sized or smaller companions; brown dwarfs and gas giants (radius$simeq$ R$_{jup}$) with periods $leq$0.2 days must certainly be rare ($<10%$). More stringent constraints requires significantly larger white dwarf samples, higher observing cadence and continuous coverage. The short duration of eclipses and transits of white dwarfs compared to the cadence of WASP observations appears to be one of the main factors limiting the detection rate in a survey optimised for planetary transits of main sequence stars.
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We have performed extensive simulations to explore the possibility of detecting eclipses and transits of close, sub-stellar and planetary companions to white dwarfs in WASP light-curves. Our simulations cover companions $sim0.3Re<{rm R}_{pl}<12Re$ an
d orbital periods $2{rm h}<P<15{rm d}$, equivalent to orbital radii $0.003{rm AU} < a < 0.1{rm AU}$. For Gaussian random noise WASP is sensitive to transits by companions as small as the Moon orbiting a $textrm{V}simeq$12 white dwarf. For fainter white dwarfs WASP is sensitive to increasingly larger radius bodies. However, in the presence of correlated noise structure in the light-curves the sensitivity drops, although Earth-sized companions remain detectable in principle even in low S/N data. Mars-sized, and even Mercury-sized bodies yield reasonable detection rates in high-quality light-curves with little residual noise. We searched for eclipses and transit signals in long-term light-curves of a sample of 194 white dwarfs resulting from a cross-correlation of the McCook $&$ Sion catalogue and the WASP archive. No evidence for eclipsing or transiting sub-stellar and planetary companions was found. We used this non-detection and results from our simulations to place tentative upper limits to the frequency of such objects in close orbits at white dwarfs. While only weak limits can be placed on the likely frequency of Earth-sized or smaller companions, brown dwarfs and gas giants (radius $approx Rjup$) with periods $<0.1-0.2$ days must certainly be rare ($<10%$). More stringent constraints likely requires significantly larger white dwarf samples, higher observing cadence and continuous coverage. The short duration of eclipses and transits of white dwarfs compared to the cadence of WASP observations appears to be one of the main factors limiting the detection rate in a survey optimised for planetary transits of main sequence stars.
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