Detection of Extrasolar Planets through Gravitational Microlensing and

Detection of Extrasolar Planets through Gravitational Microlensing and Timing Method Technique & Results

A Brief History of Light Deflection In 1911 Einstein derived: a= 2 GM סּ c 2 R = 0. 87 arcsec סּ Einstein in 1911 was only half right ! In 1916 using General Relativity Einstein derived: a= 4 GM c 2 r Light passing a distance r from object = 1. 74 arcsec Factor of 2 due to spatial curvature which is missed if light is treated like particles

Eddington‘s 1919 Eclipse expedition confirmed Einstein‘s result

A Brief History of Light Deflection In 1924 Chwolson mentioned the idea of a „factious double star. “ In the symmetric case of a star exactly behind a star a circular image would result In 1936 Einstein reported about the appearance of a „luminous“ circle of perfect alignment between the source and the lens: „Einstein Ring“ In 1937 Zwicky pointed out that galaxies are more likely to be gravitationally lensed than a star and one can use the gravitational lens as a telescope

Evidence for gravitational lensing first appeared in extragalactic work Einstein Cross Einstein Ring

Basics of Lensing: Source Lens Observer S 2 S S 1

Basics of Lensing: The Einstein Radius ≈ 1 milli-arcsecond Lens => Microlensing S 1 q. E qs S 2 Source off-centered Source centered

b = q – a(q) b=0

Magnification due to Microlensing: Typical microlensing events last from a few weeks to a few months

Time sequence: single star • Top panel shows stellar images at ~1 mas resolution centered on lens star • Einstein ring in green • Magnified stellar images shown in blue • Unmagnified image is red outline • The observable total magnification is shown in the bottom panel Animation by Scott Gaudi: http: //www. astronomy. ohio-state. edu/~gaudi/movies. html

Time sequence: star + planet • A planet in the shaded (purple) region gives a detectable deviation A planet lensing event lasts 10 -30 hours

Mao & Paczynski (1992) propose that star-planet systems will also act as lenses

Successful Microlensing Programs • OGLE: Optical Gravitational Lens Experiment (http: //www. astrouw. edu. pl/~ogle/) • 1. 3 m telescope looking into the galactic bulge • Mosaic of 8 CCDs: 35‘ x 35‘ field • Typical magnitude: V = 15 -19 • Designed for Gravitational Microlensing • First planet discovered with the microlensing method

Problem: Only 4 points!

Solution: Multi-site Campaigns

Microlensing Results: 12 Planets so far Rumor has it that there another ~20 planet candidates

The First Planet Candidate: OGLE-235 -MOA 53 OGLE alert

Lightcurve close-up & fit (from Bennet) • Cyan curve is the best fit single lens model – 2 = 651 • Magenta curve is the best fit model w/ mass fraction e 0. 03 – 2 = 323 • 7 days inside caustic = 0. 12 t. E – Long for a planet, – but mag = only 20 -25% – as expected for a planet near the Einstein Ring

The First Planet Candidate: OGLE-235 -MOA 53 1 st definitive lensing planetary discovery - complete coverage not required for characterization Real-time data monitoring was critical! S. Gaudi video

OGLE 2005 -BLG-071 Udalski et al. 2005 The Star: BASED ON GALACTIC MODEL M = 0. 46 M סּ d = 3300 pc I-mag = 19. 5 The Planet: M = 3. 5 MJup a = 3. 6 AU

OGLE-06 -109 L Features 1, 2, 3, 5 are caused by Saturn mass planet near Einstein radius. Feature 4 by another Jovian planet The Star: M = 0. 5 M סּ d = 1490 pc I-mag = 17. 17 Gaudi et al. 2008, Science, 319, 927 The Planets: M 1 = 0. 71 MJup a 1 = 2. 3 AU M 2 = 0. 27 MJup a 2=4. 6 AU

From The Astrophysical Journal Letters 644(1): L 37–L 40. © 2006 by The American Astronomical Society. For permission to reuse, contact journalpermissions@press. uchicago. edu. OGLE-2005 -BLG-169 The Star: The Planet: M = 0. 49 M סּ M = 0. 04 MJ d = 2700 pc a = 2. 8 AU I-mag = 20. 4 Fig. 1. —Top: Data and best-fit model for OGLE-2005 -BLG-169. Bottom: Difference between this model and a single-lens model with the same (t 0, u 0, t. E, ρ). It displays the classical form of a caustic entrance/exit that is often seen in binary microlensing events, where the amplitudes and timescales are several orders of magnitude larger than seen here. MDM data trace the characteristic slope change at the caustic exit (Δt = 0. 092) extremely well, while the entrance is tracked by a single point (Δt = − 0. 1427). The dashed line indicates the time t 0. Inset: Source path through the caustic geometry. The source size ρ is indicated.

Microlensing planet detection of a Super Earth? Best binary source OGLE-2005 -BLG-390 Mass = 2. 80 – 10 Mearth a = 2. 0 – 4. 1 AU q = 7. 6 x 10– 5 Ratio between planet and star

MOA-2007 -BLG-192 -L The Star (brown dwarf): M = 0. 06 M סּ d = 1000 pc J-mag = 19. 6 The Planet: M = 3. 3 Mearth a = 0. 62 AU Is it or isn‘t it a Super Earth? Best fit stellar binary

OGLE-2007 -BLG-368

Mass star ~ 0. 2 Msun Mass planet ~ 2. 6 MJupiter

To get the mass of the host star one must once again rely on statistics including a galactic model of the distribution of stars in the galaxy Stellar mass ranges from 0. 05 Msun (brown dwarf) to 0. 2 Msun (star) Mplanet = 0. 07 – 0. 49 MJupiter Semi-major axis = 1. 1 – 2. 7 AU Both at only the 90% confidence level. Red line: constraints from galactic model Black: constraints from observations with the Very Large Telescope

Microlensing Planets Planet Mass (MJ) Period (yrs) a (AU) e M* (Msun) Dstar (pcs) OGLE 235 -MOA 53 b ~2. 6 ~15 ~5 ? 0. 63 5200 OGLE-05 -071 L b ~3. 5 ~10 ~3. 6 ? 0. 64 3300 OGLE-05 -169 L b 0. 04 ~9 ~2. 8 ? 0. 49 2700 OGLE-05 -390 L b 0. 017 ~9. 6 ~2. 1 ? 0. 22 6500 MOA-2007 -BLG-192 -L b 0. 01 ~2 0. 62 ? 0. 06 1000 OGLE-06 -109 L b 0. 71 ~5 2. 3 ? 0. 5 1490 OGLE-06 -109 L c 0. 27 ~14 4. 6 0. 11 0. 5 1490 MOA-2007 -BLG-400 -L b 0. 9 - 0. 5 OGLE-2007 -BLG-368 L b 0. 07 - 3. 3 MOA-2008 -BLG-310 -L b 0. 23 - MOA-2008 -BLG-387 -L b 2. 6 -1. 8 0. 35 6000 1. 25 0. 67 >6000 3. 6 0. 19 ~5700

• Microlensing has discovered 4 -5 cold Neptunes/Superearths • Neptune-mass planets beyond the snowline are at least 3 times more common than for Jupiter- mass planets But…. this is based on small number statistics

The Advantages of Microlensing Searches • No bias for nearby stars, planets around solar-type stars • Sensitive to Earth-mass planets using ground-based observations: one of few methods that can do this • Most sensitive for planets in the „lensing zone“, 0. 6 < a < 2 AU for stars in the bulge. This is the habitable zone! • Can get good statistics on Earth mass planets in the habitable zone of stars • Multiple systems can be detected at the same time • Detection of free floating planets possible Microlensing is complementary to other techniques

From The Astrophysical Journal Letters 644(1): L 37–L 40. © 2006 by The American Astronomical Society. For permission to reuse, contact journalpermissions@press. uchicago. edu. Fig. 3. — Exoplanet discovery potential and detections as functions of planet mass and semimajor axis. Potential is shown for current ground-based RV (yellow) and, very approximately, microlensing (red) experiments, as well as future space-based transit (cyan), astrometric (green), and microlensing (peach) missions. Planets discovered using the transit (blue), RV (black), and microlensing (magenta) techniques are shown as individual points, with OGLE-2005 -BLG-169 Lb displayed as an open symbol. Solar system planets are indicated by their initials for comparison.

The Disadvantages of Microlensing Searches • Probability of lensing events small but overcome by looking at lots of stars • One time event, no possibility to confirm, or improve measurements • Duration of events is hours to days. Need coordinated observations from many observatories • Planet hosting star is distant: Detailed studies of the host star very dfficult • Precise orbital parameters of the planet not possible • Light curves are complex: only one crossing of the caustic. No unique solution and often a non-planet can also model the light curves • Final masses of planet and host stars rely on galactic models and statistics and are poorly known • Future characterization studies of the planet are impossible

2. The Timing Method

The Technique: If you have a very stable “clock” that sends a signal with a constant pulse rate and the capability to measure the time of arrival (TOA) of the signal with very high precision ÞSearch for systematic deviations in the TOAs that indicate different light travel times due to orbital motion

Timing Variations: Don’t forget to take into account your own motion!!! Due to the orbital motion the distance the Earth changes. time This causes differences in the light travel time Change in arrival time = apmpsini M* c ap, mp = semimajor axis, mass of planet

A Pulsar: a very stable astronomical clock! radiation Strong magnetic field Acts like a cosmic lighthouse Rotation periods of pulsars < 10 second The fastest rotators are millisecond pulsars: PSR 1257+12: P = 0. 00621853193177 +/- 0. 00000001 s

The (Really) First Exoplanets: in 1992 Arecibo Radio-telescope

98 d orbit removed, 66 d orbit remains 66 d orbit removed, 98 d orbit remains

PSR 1257+12 system: Planet A: M = 0. 02 M_Earth P = 25. 3 d ; a = 0. 19 AU Planet B: M = 4. 3 M_Earth P = 66. 5 d ; a = 0. 36 AU Planet C: M = 3. 9 M_Earth P = 98. 2 d ; a = 0. 46 AU fourth companion with very low mass and P~3. 5 yrs Interaction between B & C Confirms the planets and Establishes true masses!

Other applications of the timing method: • • Stably pulsating white dwarfs (P~200 s) Pulsating sd. B stars (P~500 s) Eclipse timing Transit time variations NN Ser eclipses Kepler-9 transits

Timing Method Summary: • • First successful detection technique! Requires a suitable target (clock) Lack of large sample => not efficient In best case (very short periods) is sensitive to Earth-mass planets