Frequency of solar system analogues from microlensing

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Frequency of solar system analogues from microlensing

Post by Sirius_Alpha on 5th January 2010, 9:22 pm

Frequency of Solar-Like Systems and of Ice and Gas Giants Beyond the Snow Line from High-Magnification Microlensing Events in 2005-2008
http://arxiv.org/abs/1001.0572

Abstract wrote:We present the first measurement of planet frequency beyond the "snow line" for planet/star mass-ratios[-4.5<log q<-2]: d^2 N/dlog q/dlog s=(0.36+-0.15)/dex^2 at mean mass ratio q=5e-4, and consistent with being flat in log projected separation, s. Our result is based on a sample of 6 planets detected from intensive follow-up of high-mag (A>200) microlensing events during 2005-8. The sample host stars have typical mass M_host 0.5 Msun, and detection is sensitive to planets over a range of projected separations (R_E/s_max,R_E*s_max), where R_E 3.5 AU sqrt(M_host/Msun) is the Einstein radius and s_max (q/5e-5)^{2/3}, corresponding to deprojected separations ~3 times the "snow line". Though frenetic, the observations constitute a "controlled experiment", which permits measurement of absolute planet frequency. High-mag events are rare, but the high-mag channel is efficient: half of high-mag events were successfully monitored and half of these yielded planet detections. The planet frequency derived from microlensing is a factor 7 larger than from RV studies at factor ~25 smaller separations [2<P<2000 days]. However, this difference is basically consistent with the gradient derived from RV studies (when extrapolated well beyond the separations from which it is measured). This suggests a universal separation distribution across 2 dex in semi-major axis, 2 dex in mass ratio, and 0.3 dex in host mass. Finally, if all planetary systems were "analogs" of the Solar System, our sample would have yielded 18.2 planets (11.4 "Jupiters", 6.4 "Saturns", 0.3 "Uranuses", 0.2 "Neptunes") including 6.1 systems with 2 or more planet detections. This compares to 6 planets including one 2-planet system in the actual sample, implying a first estimate of 1/6 for the frequency of solar-like systems.

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Re: Frequency of solar system analogues from microlensing

Post by Lazarus on 6th January 2010, 2:36 pm

Comes out quite favourably compared to the frequency of hot Jupiters, no?

Also a reference to an upcoming microlensing planet detection in a system which contains a third body "certainly not in the mass range being probed in the current analysis".

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Re: Frequency of solar system analogues from microlensing

Post by Sirius_Alpha on 8th January 2010, 4:34 pm

It may be worth pointing out that the microlensing events are around sub-stellar mass stars, which may have had disks of less mass than our solar system. Furthermore, aren't the stars in the bulge of sub-stellar metallicity anyway? I'm beginning to think that the observed relative deficit of planets perhaps should have been expected.

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Re: Frequency of solar system analogues from microlensing

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