for Searching Exo-Earths through Gravitational Microlensing
Dharmesh Jain Presentation for PHY 688 Instructor: Prof. Stanimir Metchev Department of Physics & Astronomy SUNY @ Stony Brook
Outline
Gravitational Lensing Gravitational Microlensing Exo-Planet Detections So Far And Beyond Review
Gravitational Lensing: History
A. S. Eddington (1920) Possibility of multiple star images O. Chwolson (1924) Ring-shaped image of a star A. Einstein (1936)[1] Discussion of both effects in less than a page (which is comprehensible!) A. Einstein (1912) Had done the calculations but not convinced it was observationally feasible (so back to GTR) First confirmed gravitationally lensed object (1979): Twin Quasar (QSO 0957+561) Bohdan Paczyski (1986, 1991): Microlensing application to dark matter and planetary searches First microlensing event (1993): towards Large Magellanic Cloud First planet detection (2003): OGLE-2003-BLG-235
[2] J. Renn et al
Gravitational Lensing: Basics
Lensing effect due to the gravitational field of a massive object (galaxy) present between source object (quasar) and observer (us). Numerous distorted images of the source object, and/or Amplification of intensity of the image. Types:
1. Strong Lensing: Image Distortion and Intensity Amplification. 2. Weak Lensing: Image Distortion at a weaker scale. 3. Microlensing: Only Intensity Amplification detectable.
Gravitational Lensing: Theory
Light deflection angle,
IDS=DLS+SDS I-S=(4GML/c2IDL)(DLS/DS) I2-SI-E2=0 =[S(S2+4E2)] Knowing gives ML Einstein radius, rE=EDL Einstein ring crossing time, tE=rE/v
[7] A. Gould
Examples-I
JVAS B1938+666 Quad-image lensing of three sources! Two sources contributing to Einstein ring One source producing two offset images.
Ref-3
Gravitational lensing: Theory-I
uS/E u/E A=|udu/udu| A=A++A-
Intensity Amplification, A(t)=(u2+2)/[u(u2+4)] Impact parameter, u(t)=[umin2+((t-t0)/tE)2] rE=4.42 AU[(ML/0.3M)(DS/8Kpc)(x(1-x))] tE=38.25d(200Km.s-1/v)[]
[6] N. J. Rattenbury
Examples-II
Two lensed images of a single quasar source due to a galaxy. [Ref-4]
EINSTEIN CROSS at two different epochs. [Ref-5]
Gravitational lensing: Theory-II
Lens Eq: Y=X-mi(X-xi)/|X-xi|2 Critical: X such that det J=0 Caustic: Y=f(Xcritical ) A= Aj ; Aj=|det J(xj)|-1
q=MP/ML=10-3 Projected radius, d=1.4 umin=0.01 & 0.2 =135 & 106
[6] N. J. Rattenbury
Gravitational lensing: Theory-III
Low amplification caustic crossing event and corresponding microlensing light curve.
[6] N. J. Rattenbury; [8] S. Gaudi
Gravitational lensing: Theory-IV
High amplification caustic crossing event and corresponding microlensing light curve.
[6] N. J. Rattenbury; [8] S. Gaudi
Exo-Planet Detection-I
OGLE-2003-BLG-235/MOA-2003-BLG-53
Models: Cyan- Single lens model Magenta- q>0.03 Green- Early Caustic Crossing Model Black- Best Fit Model Parameters: umin, tE, t0, q, d, Rs, . Results: MP=1.5MJ (q=3.910-3) at 3.0AU (d=1.12) from the star.
[6] N. J. Rattenbury
Exo-Planet amplification Detection-II
OGLE-2005-BLG-071
High caustic cusp crossing event. Results: q=7.110-3 d=1.294
[7] A. Gould
Exo-Planet Detection-III
OGLE-2006-BLG-109
Both high & low amplification events occur (5 times!) Two Planets! 1, 2, 3 & 5: Saturn 4: Jupiter
[7] A. Gould
So What???
Comparing exo-planets discovered through Transits, Radial Velocity and lensing: Small probability / Short event duration No Detailed investigations / Independent confirmations possible Only q and d determinable!
[7] A. Gould
Resolving Issues
Amplitude of planetary microlensing signals is large (>10%) and is approximately independent of the planets mass. Sensitive to low-mass planets down to 0.1 M. Sensitive to planets at 1.5-4 AU from their host stars near the snow line.
Planets with large semi-major axes detectable easily!
Not detecting light from either the planet or its host star, so planets orbiting unseen stars can be detected. Multiple planet systems are detectable. Even detecting free-floating planets is possible. No bias for nearby or main sequence stars. Best statistics for galactic population of planets.
Surveys: Present & Future-I
OGLE (Optical Gravitational Lensing Experiment)
1.3m telescope at La Silla, Chile Field view 0.34(?) sq.deg.
MOA/MOA-II (Microlensing Observations in Astrophysics)
1.8m telescope at Mt. John, New Zealand Field view 2.2 sq.deg.
Earth Hunter Network (EHN)
Four 2m telescopes around the Earth Field view 4 sq.deg.
[6] N. J. Rattenbury
Surveys: Present & Future-II
Microlensing Planet Finder (MPF) Space-based mission (1.1m telescope/1.5 deg FoV) Sensitive to Earth-mass planets in habitable zone! 10-100 events/year expected (<10 for ground-based!) Feb. 2012 launch
[6] N. J. Rattenbury; [9] D. Benne...