Transcript Microlensing in NZ

The mass of the free-floating
planet MOA-2011-BLG-274L
Philip Yock
18th International Conference on Gravitational Lensing
LCOGT, Santa Barbara
January 2014
Free-floating planets?
Sidney Liebes, “Gravitational Lenses”, Physical Review, 10 Feb 1964:“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.”
Lens 1000 × lighter than normal, therefore ring 30 × smaller,
magnification 30 × less and duration 30 × shorter
51 years later
at Farm Cove Observatory,
Auckland, NZ
Fleeting duration
Flat top
Free-floater?
Choi et al ApJ 751, 41
Mass measurement?
Terrestrial parallax?
Australia & NZ
Six telescopes
2 days
4 hours
Source star
(V-I)s,0 = 0.76 ± 0.10 and Is,0 = 17.96 ± 0.1
Hence rs = 1.47 ± 0.24 rsolar, MI = 3.47 ± 0.20 and Teff = 5700 ± 200 K
Marginalization plots
Provide accuracies of umin, ρ, t0 and tE in the usual manner
Air-mass effects
Farm Cove (Auckland)
14º ± 6º
PEST (Perth)
56º - 31º
Finite 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 al
ApJ 751, 41 (2012)
ρ large
tE 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 parallax
Terrestrial parallax is large, implying the lens is nearby,
the Einstein ring is small and the lens-mass is low
Negative umin
umin > 0
πE ~ 13
δκ2 ~ 9
umin < 0
πE ~ 8
δκ2 ~ 6
Cooler and hotter source star
5500K
5700K
5900K
πE ~ 12
δκ2 ~ 9
πE ~ 13
δκ2 ~ 9
πE ~ 13
δκ2 ~ 10
Lens distance and mass
(Preliminary calculations from on-line
reduction of the MOA data)
Trajectory
Impact parameter = umin × rE (at observer plane)
= 5.8 Earth radii
Direction = 12º west of north
(Second solution to the west)
Parallax from single telescopes
Multi telescope solution
Single telescope fits
Free of systematic effects
(Preliminary analysis with on-line
reduction of MOA images)
Orbital parallax distorts the light curve
(4 second effect)
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?
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 rate





A couple of transit events are detected per year with normal lenses and main sequence
source stars
Hence a few transit events should occur per year with free-floating planets and main
sequence sources
Duration is shorter, magnification is less, and the lens must be nearby for a mass
measurement.
Detection rate will be low - a challenge for LCOGT
But can be done simultaneously while monitoring high mag events:-
Thanks