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Frequency of Solar-like Systems and of Ice and Gas and Giants Beyond the Snow Line from High-magnification Microlensing Events in 2005-2008


Gould, A and Dong, S and Gaudi, BS and Udalski, A and Bond, AI and Greenhill, J and Street, RA and Dominick, M and Sumi, T and Szymanski, MK and Han, C and Allen, W and Bolt, G and Bos, M and Christie, GW and DePoy, DL and Drummond, J and Eastman, JD and Gal-Yam, A and Higgins, D and Janczak, J and Kaspi, S and Kozlowski, S and Lee, CU and Mallia, F and Maury, A and Maoz, D and McCormick, J and Monard, LAG and Moorhouse, D and Morgan, N and Natusch, T and Ofek, EO and Park, BG and Pogge, RW and Polishook, D and Santallo, R and Shporer, A and Spector, O and Thornley, G and Yee, JC and Kubiak, M and Pietrzynski, G and Soszynski, I and Szewczyk, O and Wyrzykowski, E and Ulaczyk, K and Poleski, R and Abe, F and Bennett, DP and Botzier, CS and Douchin, D and Freeman, M and Fukui, A and Furusawa, K and Hearnshaw, JB and Hosaka, S and Itow, Y and Kamiya, K and Kilmartin, PM and Korpela, A and Lin, W and Ling, CH and Makita, S and Masuda, K and Matsubara, Y and Miyake, N and Muraki, Y and Nagaya, M and Nishimoto, K and Ohnishi, K and Okumura, T and Perrott, YC and Philpott, L and Rattenbury, N and Saito, To and Sako, T and Sullivan, DJ and Sweatman, WL and Tristram, PJ and von Seggern, E and Yock, PCM and Albrow, M and Batista, V and Beaulieu, JP and Brillant, S and Caldwell, J and Calitz, JJ and Cassan, A and Cole, A and Cook, K and Coutures, C and Dieters, S and Prester, DD and Donatowicz, J and Fouque, P and Hill, K and Hoffman, M and Jablonski, F and Kane, SR and Kains, N and Kubas, D and Marquette, JB and Martin, R and Martioli, E and Meintjes, P and Menzies, J and Pedretti, E and Pollard, K and Sahu, KC and Vinter, C and Wambsganss, J and Watson, R and Williams, A and Zub, M and Allan, A and Bode, MF and Bramich, DM and Burgdorf, MJ and Clay, N and Fraser, S and Hawkins, E and Horne, K and Kerins, E and Lister, TA and Mottram, C and Saunders, ES and Snodgrass, C and Steele, IA and Tsapras, Y and Jorgensen, UG and Anguita, T and Bozza, V and Novati, SC and Harpsoe, K and Hinse, TC and Hundertmark, M and Kjaergaard, P and Liebig, C and Mancini, L and Masi, G and Mathiasen, M and Rahvar, S and Ricci, D and Scarpetta, G and Southworth, J and Surdej, J and Thorne, CC, Frequency of Solar-like Systems and of Ice and Gas and Giants Beyond the Snow Line from High-magnification Microlensing Events in 2005-2008, Astrophysical Journal, 720, (2) pp. 1073-1089. ISSN 0004-637X (2010) [Refereed Article]

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© 2010 The American Astronomical Society

DOI: doi:10.1088/0004-637X/720/2/1073


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 M host ~ 0.5 M , and detection is sensitive to planets over a range of planet-star-projected separations (s –1 max R E, s max R E), where R E ~ 3.5 AU(M host/M )1/2 is the Einstein radius and s max ~ (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.

Item Details

Item Type:Refereed Article
Keywords:gravitational lensing: micro; planetary systems
Research Division:Physical Sciences
Research Group:Astronomical sciences
Research Field:Stellar astronomy and planetary systems
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the physical sciences
UTAS Author:Greenhill, J (Dr John Greenhill)
UTAS Author:Cole, A (Professor Andrew Cole)
UTAS Author:Hill, K (Dr Kym Hill)
UTAS Author:Watson, R (Dr Bob Watson)
ID Code:65183
Year Published:2010
Web of Science® Times Cited:239
Deposited By:Physics
Deposited On:2010-10-11
Last Modified:2014-10-29

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