FREQUENCY OF SOLAR-LIKE SYSTEMS AND OF ICE AND GAS GIANTS BEYOND THE SNOW LINE FROM HIGH-MAGNIFICATION MICROLENSING EVENTS IN 2005–2008

By A. Gould, S. Dong, B. Gaudi, A. Udalski, I. Bond, J. Greenhill, R. Street, M. Dominik, T. Sumi, M. Szymański and 138 more. 2010

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We present the first measurement of the planet frequency beyond the “snow line,” for the planet-to-star mass-ratio interval −4.5 < log q < −2, corresponding to the range of ice giants to gas giants. We find at the mean mass ratio q = 5 × 10−4 with no discernible deviation from a flat (Öpik's law) distribution in log-projected separation s. The determination is based on a sample of six planets detected from intensive follow-up observations of high-magnification (A>200) microlensing events during 2005–2008. The sampled host stars have a typical mass Mhost ∼ 0.5 M☉, and detection is sensitive to planets over a range of planet–star-projected separations (s−1maxRE, smaxRE), where RE ∼ 3.5 AU(Mhost/M☉)1/2 is the Einstein radius and smax ∼ (q/10−4.3)1/3. This corresponds to deprojected separations roughly three times the “snow line.” We show that the observations of these events have the properties of a “controlled experiment,” which is what permits measurement of absolute planet frequency. High-magnification events are rare, but the survey-plus-follow-up high-magnification channel is very efficient: half of all high-mag events were successfully monitored and half of these yielded planet detections. The extremely high sensitivity of high-mag events leads to a policy of monitoring them as intensively as possible, independent of whether they show evidence of planets. This is what allows us to construct an unbiased sample. The planet frequency derived from microlensing is a factor 8 larger than the one derived from Doppler studies at factor ∼25 smaller star–planet separations (i.e., periods 2–2000 days). However, this difference is basically consistent with the gradient derived from Doppler studies (when extrapolated well beyond the separations from which it is measured). This suggests a universal separation distribution across 2 dex in planet–star separation, 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 two or more planet detections. This compares to six planets including one two-planet system in the actual sample, implying a first estimate of 1/6 for the frequency of solar-like systems.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/9a7f6a370ee10b86a1ee85e3b1a912b7113e73b6

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Citations in the corpus

• The Occurrence and Architecture of Exoplanetary Systems (2014, background): “Gould et al. (2010) analyzed a sample of 13 microlensing events which led to 6 planet discoveries, allowing a measurement of the frequency of planets with planet-to-star mass ratios q ∼ 10−4 (probably Neptune-mass planets around M dwarfs) and sky-projected orbital separations s ∼ 3 AU.”
• PLANETS AROUND LOW-MASS STARS (PALMS). IV. THE OUTER ARCHITECTURE OF M DWARF PLANETARY SYSTEMS (2014, background): “Moreover, the logarithmicallyflat forms are broadly consistent with the projected separation distribution and mass distribution for planets around M dwarfs found in microlensing surveys (Gould et al. 2010; Cassan et al. 2012).”
• Predictions of the WFIRST Microlensing Survey. I. Bound Planet Detection Rates (2018, background): “…but radial velocity surveys tend to show an increase in planet occurrence with log semimajor axis or log period (e.g., Cumming et al. 2008; Bonfils et al. 2013) that appears to be 33 consistent with microlensing occurrence rates when extrapolated (see, e.g., Gould et al. 2010; Suzuki et al. 2016).”
• MOA-2009-BLG-387Lb: a massive planet orbiting an M dwarf (2011, background): “Indeed, based on the analysis of 13 well-monitored high-magnification events with 6 detected planets, Gould et al. (2010) found that the frequency of giant planets at separations of ∼2.5 AU orbiting ∼0.5 M hosts was quite high and, in particular, consistent with the extrapolation of the frequencies…”
• Microlensing Surveys for Exoplanets (2012, background): “Both panels are adapted from Gould et al. (2010) and reproduced by permission of the AAS. dwarf mass function, which they interpret as due to a population of unbound or wide-separation Jupiter-mass objects.”
• HATSouth: A Global Network of Fully Automated Identical Wide-Field Telescopes (2012, background): “While other planetdetection methods, such as microlensing, have proven to be efficient at discovering long-period and low-mass planets (Gould et al. 2010; Dong et al. 2009), these methods are primarily useful for studying the statistical distributions of periods and masses of planets, and cannot be…”
• TESTING IN SITU ASSEMBLY WITH THE KEPLER PLANET CANDIDATE SAMPLE (2013, background): “…but planets in the Uranus/Neptune mass range (10–100 M⊕) have also been found with a range of semimajor axes, both close in (Howard et al. 2010; Mayor et al. 2011; Borucki et al. 2010; Holman et al. 2010; Lissauer et al. 2011a) and at large separations (Gould et al. 2006, 2010; Sumi et al. 2010).”
• Debris disks as signposts of terrestrial planet formation (2011, background): “The actual distribution of giant planets at Jupiter-Saturn distances is unknown, although observational constraints predict that at least 10%, and perhaps more than 50%, of stars have giant planets at these separations (Cumming et al. 2008; Gould et al. 2010).”
• BREEDING SUPER-EARTHS AND BIRTHING SUPER-PUFFS IN TRANSITIONAL DISKS (2015, background): “…is roughly flat with orbital distance — that super-Earths are truly ubiquitous — as appears to be the case for M stars, as revealed by microlensing (e.g., Sumi et al. 2010; Gould et al. 2010; Cassan et al. 2012; Clanton & Gaudi 2014, 2015) and transit surveys (Dressing & Charbonneau 2015).”
• HYDROGEN GREENHOUSE PLANETS BEYOND THE HABITABLE ZONE (2011, background): “The Einstein radius of these stars is well outside the classical HZ (Sumi et al. 2010; Kubas et al. 2010) but coincides with the “ice line” where Neptune-mass or icy super-Earth planets may form (Gould et al. 2010; Mann et al. 2010).”