A. Udalski Warsaw University Observatory The Optical Gravitational Lensing Experiment (OGLE):Bohdan’s and Our Great Adventure
OGLE: The Optical Gravitational Lensing Experiment (1992 - ….) http://ogle.astrouw.edu.pl http://bulge.princeton.edu/~ogle
Three Phases of the OGLE Project • OGLE-I (1992-1995). 1 m Swope telescope at LCO • OGLE-II (1997-2000). 1.3 m Warsaw telescope • OGLE-III (2001-….). 8k x 8k mosaic CCD
OGLE – Early History • May 1990 – first ideas and talks on large scale photometric survey: SNe, 1-m class telescope at Apache Point, NM. • Early 1991 – Evolution toward microlensing and variable stars search. • Mid 1991– OGLE-I team formed. Proposal for telescope time at Las Campanas Observatory – ~50 nights granted in April – September 1992. • Fall 1991 – financing of the Warsaw Telescope accepted. • Apr. 12, 1992 – first images of OGLE-I. • ~2 million stars regularly observed.
OGLE-I Results. Microlenses: Discovery of the first events toward the GB (1993).
Microlensing Optical Depth: • First empirical determination (1994): τ = 3.3 x 10-6
Variable Stars: – Variables in the Galactic Bulge – Variable Stars in Globular Clusters (ωCen, 47 Tuc) – Variable Stars in Dwarf Galaxies: Sculptor, Sagittarius
OGLE-II • New telescope – new targets: Magellanic Clouds • New CCD Camera – drift scan mode • ~40 million stars regularly observed • Variable and non-Variable Stars in GB, MC, gravitational micro and lensing • Distance scale
Cepheids in the MC. PL relations. Hubble constant is based on OGLE PL relations
RR Lyrae ~7600 in LMC ~600 in SMC ~1900 RRab in GB
Miscellaneous Variables Heaviest stars known (>80 M_Sun) RR Lyr in eclipsing systems Double Periodic Variables
Miscellaneous PM Catalogs SNe
OGLE-III • New 8192 x 8192 pixel mosaic CCD camera (0.26 arcsec/pixel scale): 0.5 x 0.5 sq. degree • 1.3 m OGLE telescope at Las Campanas Observatory, Chile • Data Pipeline: photometry derived with image subtraction method (accuracy up to 3 mmag for the brightest stars over a few months long observing run) • OGLE back in operation on June 12, 2001 • ~200 million stars regularly observed (GB, GD, MC) • Extrasolar planets, low luminosity objects
Extrasolar Planets. • Radio techniques: Pulsar planets. • Spectroscopy: First solar type planets. (51 Peg). ~230 known (< 200pc). • Transit technique: About 20 transiting planets known (five OGLE detections). • Microlensing: Four detections (published).
Planetary Microlensing Short-lived anomaly in the light curve of a typical single mass microlensing event.
Transit Method Pros: • Photometric survey of thousands stars provides transit candidates. Characteristic shape of the light curve • r/R derived from the depth of transit. In principle R, r, i and u can be derived from the light curve (in real life r, i) • Spectroscopic follow-up provides mass (sin i ~ 1.0) • The only planetary cases with precise parameters derived (mass, radius, density) • Many potential „follow-up” observations: IR, transit spectroscopy, long term transit timing
Transit Method Problems: • High accuracy of photometric measuremens is crucial for transit detections (~0.5%) • Several individual transits must be detected to derive the photometric orbit • Not only planets can cause small depth transits: smallest stars (M type) or brown dwarfs can have similar size as Jupiter like planets. Careful spectroscopic follow-up is crucial to confirm planetary status in each case. But less spectroscopic observations is needed because the photometric orbit is known
Searches for PhotometricTransits • Follow up of spectroscopically discovered planets (example: the first ever transit detection in HD209458 – 1999) • Wide Field Surveys (several detections) • Deep Surveys: Galactic disk (five first detections of exoplanets with the transit method); Star Clusters
Wide Field Surveys Wide Field Surveys Wide Field Surveys • Wide field of ~ 5x5 sq. degree • Small telescopes (10—50 cm) • Bright objects (m<12 mag) • Small number of potential candidates • Precise photometry more difficult • Bright stars – large variety of follow-up observations (IR emission, transit spectroscopy, transit timing) • STARE, TreS, XO, HAT, WASP
Deep Surveys • Smaller field of view – typically < 1 sq. degree; large telescopes (1—4 m) • Very precise photometry of fainter stars with reasonable magnitude limit – limit of present spectroscopy (typically I ~ 16.5 mag) • Typical fields: Galactic disk (hundred thousands stars in the line of sight, located at different distances with different reddening etc.); Star Clusters (a few thousand stars located at the same distance, homogeneous, plus foreground and background contamination)
Pros and Cons • More observed stars – more candidates • Somewhat less accurate planet parameters (to be refined by next generation giant telescopes) • Smaller number of possible follow-up observations (IR, transit spectroscopy etc.).Long term transit timing OK • Study of planetary systems at much larger distance, in different environment
OGLE-III Transit Campaigns:Learning Period • Campaign #1: June-July 2001. Target: Galactic Bulge. ~65 stars with transiting objects found. Transiting objects != planetary candidates • Campaign #2: Feb.-May 2002. Target: Galactic Disk (Carina). ~70 stars with transiting objects discovered
What lessons have we learned? • Stellar background • Blending • No large planets ( R > 2 RJUP) • Jupiter-sized stars
OGLE-III Transit Campaigns:Routine Campaigns • Campaign #3 & #4 Spring-Summer 2003+2004. Target: Galactic Disk (Car, Cen, Mus). ~40 stars with transiting objects found • Campaign #5 Spring 2005. Galactic Disk (Car): ~20 good transiting objects • Campaign #6 Spring 2006. Galactic Disk (Car): ~25 good transiting objects • Campaign #7 Spring 2007. Galactic Disk (Car): data analyzed.
Spectroscopic Follow-up • OGLE Policy: results of photometric transit surveys available in public domain • Spectroscopic follow up of OGLE candidates from Campaigns #1 & #2: Konacki, Torres etal.; Bouchy, Pont, Moutou et al. • Spectroscopic follow-up of OGLE candidates from the next campaigns: Large ESO Programme