Twenty Years of Microlensing Observations

From the

Andrzej Udalski

Warsaw University Observatory

Perspective

Bohdan Paczyński (1940—2007)

Gravitational Microlensing toward the Galactic Bulge

Planetary Microlensing

Search for Gravitational Microlenses

• MACHO Project – Mt. Stromlo, Australia (1992 – 1999)

• EROS Project – ESO, Chile (1992 – 2002)

• MOA Project – Mt. Johns, New Zealand (1997– …)

• OGLE Project – Las Campanas, Chile (1992 – …)

Twenty One Years of the OGLE Survey

OGLE: The Optical Gravitational Lensing Experiment (1992 - ….)

Four Phases of the OGLE Project

• OGLE-I (1992-1995). 1 m Swope telescope at LCO. ~2 million stars observed. Microlensing

• OGLE-II (1997-2000). 1.3 m Warsaw telescope. ~40 million stars observed. Variable and non-Variable Stars in GB, MC

• OGLE-III (2001– 2009). 8k x 8k mosaic CCD. ~200 million stars observed (GB, GD, MC). Extrasolar Planets, Microlensing

• OGLE-IV (2010– ….). 32-chip 256 Mpixel mosaic CCD

http://ogle.astrouw.edu.pl

Las Campanas Observatory, Chile

Discovery of the First Microlensing Events – September 1993

OGLE-I #1

Microlenses: Discovery of the first events toward the GB (1993).

First Binary Microlensing (1994)

Fine Microlensing Effects

Early Warning System (EWS – 1994)

Follow-Up Microlensing Projects

< 2001• PLANET

• GMAN

• MOA

>= 2001• microFuN

• PLANET

• Robonet

• MindSTEP

Three Main Channels

• Search for Dark Matter• Galactic Structure• Extrasolar Planets – Planetary Microlensing

Dark Matter – MACHO in the Galactic Halo

OGLE-2005-SMC-001

OGLE MC Microlensing

Current O-IV MC Survey – 600 square degrees

LMC

SMC

Magellanic Bridge

Classical Cepheids in the Magellanic Clouds

LMC

SMC

Magellanic Bridge

RR Lyrae Stars in the Magellanic Clouds

Stellar Populations in the Magellanic Bridge

OGLE-IV Transient Detection System

Galactic Structure

• Optical depth for microlensing toward CG• High resolution spectroscopy of highly

microlensed bulge dwarfs• Microlensing in the Galactic disk

Gravitational Microlensing Optical Depth

• probably the best way to constrain the internal structure of the Milky Way

• The recent models of the Galactic Bulge: Kerins,Robin,Marshall (2010)

• OGLE >~10000 microlenses

3.2±0.8 (OGLE3 2007)

2.4±0.4 (MACHO 2000)

2.6±0.8 (MOA 2003)

Optical Depth

Microlensing in the Galactic Disk

OGLE-IV Galactic Disk (l<0)

Planetary Microlensing

OGLE-III Hardware and Software (2001)

• 1.3 m OGLE telescope at Las Campanas Observatory, Chile

• 8192 x 8192 pixel mosaic CCD camera (0.26 arcsec/pixel scale): 0.5 x 0.5 sq. degree

• Data Pipeline: photometry derived with image subtraction method (accuracy up to 3 mmag for the brightest stars over a few months long observing run)

Transiting OGLE Exoplanets

Planetary Microlensing

O-III ~600 microlensing events per year in real time since 2002.

Short-lived anomaly in the light curve of a typical single mass microlensing event.

OGLE-2003-BLG-235/MOA-2003-BLG-53First Planetary Microlensing

Planet/star mass ratio: q~0.004

OGLE-2005-BLG-71

Planet/star mass ratio: q~0.007

OGLE-2005-BLG-390

Planet/star mass ratio: q~0.00008. Mass of the planet: ~6 Earth masses. The least massive planet at the discovery

MOA-II Survey (2006– …)

Microlensing Planets – results

• ~30 microlensing planets found since the first announcement in 2004 (~20 published so far)

• First cool super-Earths of 3-10 Earth masses: low mass planets are common

• OGLE-2006-BLG-109: analog of the solar system (multiplanetary system: Jupiter+Saturn like)

• First estimations of the frequency of planets at and behind the „snow line”

• 2003– 2007: the discovery rate 0-1 exoplanets per season

• 2007–2010: the discovery rate of 2-4 exoplanets per season

Main Potential of Microlensing

• Full status and characterization of exoplanets in regions located 0.5—10 AU from Host Stars (the regions at and behind the Snow Line)

• Status of exoplanets around wide range of types of Host Stars

• Discovery of low mass planets from the ground

Second Generation Planetary Microlensing Survey

• Survey and Follow-up in one• Network of 1—2-m class telescopes over the globe with

large field (>1 square degs) cameras• Monitoring of the most microlensing efficient parts of the

Galactic bulge with the cadence of ~15 minutes• No missing planets, easier estimation of survey statistics• Estimations: A network of three 1.3—2 m telescopes: the

detection of 1—4 Earth mass planets, 10—15 super-Earths, 100 Jupiter mass planets per year

• Five year long survey should provide resonable large sample of planets for estimation of the census of exoplanets down to Earth mass at orbits of 0.5—10 AU

OGLE-IV: 2010 – ….

• 32 chip 256 Mpixel mosaic CCD camera (+ 2 chips for guiding)

• 2048 x 4102 pixel E2V 44-82 DD CCD detectors (15 m).

• 1.4 square degrees field, 0.26”/pixel

• 20 sec. reading time

• First light September 7, 2009

• Regular observations since March 4/5, 2010

OGLE-IV Nowa Kamera Mozaikowa

OGLE-IV 2012 BLG SKY

Cadence: red – up to 30 epochs/night

yellow – up to 10 epochs/night

green – up to 3 epochs/night

blue – ~1 epoch/night

cyan – ~1 epoch /2 nights

Real Time Microlensing: OGLE-IV

• 58 O-IV fields analyzed in real time including all very high and high cadence

• Statistics for 2012 BLG season: ~1700 on-line detections (~20 in O-I, ~60/season in O-II, ~600/season in O-III)

• Total number of OGLE-IV microlensing fields: 107 – they will be gradually included to EWS

OGLE-IV planetary microlenses 2010Commissioning Mode

MOA-2010-BLG-117 MOA-2010-BLG-328

MOA-2010-BLG-477 MOA-2010-BLG-523

2012 Planetary Microlensing

Free-Floating Planets

• Microlensing event characteristic time: tE=RE/vtr

• RE~sqrt(Mlens) → tE~sqrt(Mlens)• tE< 2 days – lensing object has planetary mass• High cadence observations needed for detection : (OGLE-IV:

18-60 min.)• MOA and OGLE data from 2006-2007: 10 short-lived

microlensing events of likely planetary mass. No trace of host stars: population of unbound (FFP) or very distant exoplanets.

• OGLE-IV data much better suited : preliminary estimation – 2011 season: ~40 events with tE< 2 days (shortest corespond statistically to a few Earth mass objects)

• Origin: gravitational interactions – stellar encounters, ejection of planets during planetary system formation

OGLE-IV 2013 BLG SKY

Cadence: red – up to 30 epochs/night

yellow – up to 10 epochs/night

green – up to 3 epochs/night

blue – ~1 epoch/night

cyan – ~1 epoch /2 nights

Prospects for Planetary Microlensing Field: Bright

• New facilities: Bisdee Tier Tasmania, LCOGT Network, KMNet

• Space Missions: WFIRST, EUCLID