The mass of the free-The mass of the free-floating planet MOA-floating planet MOA-

2011-BLG-274L 2011-BLG-274L

Philip YockPhilip Yock1818thth International Conference on Gravitational International Conference on Gravitational

Lensing Lensing LCOGT, Santa BarbaraLCOGT, Santa Barbara

January 2014 January 2014

Free-floating planets? Free-floating planets?

Sidney Liebes, “Gravitational Lenses”, Physical Review, 10 Feb 1964:-

Lens 1000 × lighter than normal, therefore ring 30 × smaller, magnification 30 × less and

duration 30 × shorter

“There appears little likelihood that unbound planet-sized bodies floating about the galaxy would contribute significantly to the frequency of detectable events. For, the associated pulses would be so weak and infrequent and of such fleeting duration – perhaps a few hours – as to defy detection.”

Fleeting duration Flat topFree-floater?Choi et al ApJ 751, 41

Mass measurement? Terrestrial parallax?Australia & NZ

at Farm Cove Observatory,Auckland, NZ

51 years later

Six telescopesSix telescopes

2 days 4 hours

Source starSource star

(V-I)s,0 = 0.76 ± 0.10 and Is,0 = 17.96 ± 0.1Hence rs = 1.47 ± 0.24 rsolar, MI = 3.47 ± 0.20 and Teff = 5700 ± 200 K

Marginalization plots Marginalization plots

Provide accuracies of umin, ρ, t0 and tE in the usual manner

Air-mass effectsAir-mass effectsFarm Cove (Auckland) PEST (Perth)

14º ± 6º 56º - 31º

Finite source sizeFinite source size

ρ = θs/θE = 0.01 is large, but θs is normal, hence θE small and the lens-mass is low

tE = 3 days also suggests θE is small and the lens-mass is low BUT the distance to the lens is needed

Comparison with Choi et Comparison with Choi et al al

ApJ 751, 41 (2012) ApJ 751, 41 (2012)

ρ largetE small µ large

}Suggest the mass of the lens is low

But we need to know the distance the distance to the lens to determine its mass

Terrestrial parallaxTerrestrial parallax

Terrestrial parallax is large, implying the lens is nearby,the Einstein ring is small and the lens-mass is low

Negative uminNegative umin

umin > 0 umin < 0

πE ~ 13 πE ~ 8 δκ2 ~ 9 δκ2 ~ 6

Cooler and hotter source Cooler and hotter source starstar

5500K 5700K 5900K

πE ~ 12 πE ~ 13 πE ~ 13δκ2 ~ 9 δκ2 ~ 9 δκ2 ~ 10

Lens distance and mass Lens distance and mass

(Preliminary calculations from on-line reduction of the MOA data)

TrajectoryTrajectory

Impact parameter = umin × rE (at observer plane)

= 5.8 Earth radii

Direction = 12º west of north

(Second solution to the west)

Parallax from single Parallax from single telescopes telescopes

Single telescope fits

Multi telescope solution

Free of systematic effects

(Preliminary analysis with on-line reduction of MOA images)

Orbital parallax distorts the Orbital parallax distorts the light curvelight curve

(4 second effect)

Host star?Host star?Caustic formed by a planet and a distant star

If the caustic fits inside the source star the source star is undetectable. No host within 37 AU

Exomoons?Exomoons?

δκ2 = 110 for moon detection Exclusion region slightly larger than found by Choi et al. Above is for mass ratio 3×10-4. Ganymede not detectable.

Event rateEvent rate A couple of transit events are detected per year with normal A couple of transit events are detected per year with normal

lenses and main sequence source starslenses and main sequence source stars Hence a few transit events should occur per year with free-Hence a few transit events should occur per year with free-

floating planets and main sequence sources floating planets and main sequence sources Duration is shorter, magnification is less, and the lens must be Duration is shorter, magnification is less, and the lens must be

nearby for a mass measurement.nearby for a mass measurement. Detection rate will be low - a challenge for LCOGTDetection rate will be low - a challenge for LCOGT But can be done simultaneously while monitoring high mag But can be done simultaneously while monitoring high mag

events:- events:-

ThanThanksks