Other Science from Microlensing Surveys I or Microlenses as Stellar Probes By Jonathan Devor

Overview of the talk  The problem with “vanilla” microlensing  “Non-vanilla” microlensing effects: (1) Parallax (2) Limb darkening (3) A planet around the lens (4) A planet around the source

The problem with vanilla Not enough information in “vanilla” lensing events Observable parameters: 1.Time of max (t 0 ) 2.Time scale (t E ) 3.Max magnification PLANET data + fits Paczynski curves:

…now add some sprinkles and fudge tEtE EROS BLG t star

The solution Scale of source: Source star characteristics: {color, magnitude and spectrum} D source R source θ source Scale of lens: Relative proper motion ( lens-source ): Astrometry: R lens D lens M lens

Astrometry of weighted mean position Lens at origin Source at origin

SIM: “ Will determine the positions and distances of stars several hundred times more accurately than any previous program. ” Baseline10 m Wavelength range µ m Telescope Aperture0.3 m diameter OrbitEarth-trailing solar orbit Mission Duration5 years (launch in 2009) Narrow Angle Astrometry1 µ as single measurement accuracy (goal) Limiting Magnitude20 mag (goal)

(1) Parallax images source centroid Centroid path Astrometric path

Observations: OGLE 99-BLG-32

(2) Limb darkening  You see deeper into a star at the center of it’s disk, then you see at it’s edge. Hot Cool  The limb of a stellar disk is almost always redder/dimmer than the center.

Chromatic Lensing

Observations of H α absorption line equivalent widths

Binary Lenses – brief recap

Choose the line of sight

Observation: EROS BLG

(3) Planet around the lens

…animated

Planet inside the Einstein radius

…now take a closer look

Changing the location of the planet

(4) A planet around the source Source: G0 V star at 8 kpc

Planet finding comparison Planet around the lens Planet around the source Underlying method Use the background source as a projector Use the intervening lens as a natural telescope What can be learned Mass Location (orbit) Radius Brightness Atmosphere Rings, etc. follow-upno difficulty Comparably easy (even for small planets) Very difficult ~1% photometric effect

Summary  Very little information can be learned from purely “vanilla” lensing. You need other effects to break the degeneracy and pin down the system’s physics.  The parallax effect occurs in all cases, but can only be readily detected in very long time scale events (~year) and when the lens is relatively nearby.  Through lensing it is possible to learn about source star’s limb darkening, surface features and planets. Unfortunately the latter is very difficult to do.  Planets around the lensing star should be far easier to detect, unfortunately we won’t be able to learn that much about them.  A microlensing event only happens once, so “real-time astronomy” is required to gather enough data before it’s gone. (You snooze- you loose)

References  Afonso, C., et al., Photometric constraints on microlens spectroscopy of EROS-BLG , Astronomy and Astrophysics, v.378, p (2001)  An, J. H., First Microlens Mass Measurement: PLANET Photometry of EROS BLG , The Astrophysical Journal, Volume 572, Issue 1, pp (2002)  Cassan, A., Probing the atmosphere of the bulge G5III star OGLE-2002-BUL-069 by analysis of microlense H alpha line, astro-ph/ (2004)  Evans, N. W., The First Heroic Decade of Microlensing, astro-ph/ (2002)  Gaudi, B. S., Microlensing Searches for Extrasolar Planets: Current Status and Future Prospects, astro-ph/ (2002)  Gaudi, B. S. et al., Microlensing Constraints on the Frequency of Jupiter-Mass Companions: Analysis of 5 Years of PLANET Photometry, The Astrophysical Journal, Volume 566, Issue 1, pp (2002)  Gaudi, B. S. et al., Angular Radii of Stars via Microlensing, The Astrophysical Journal, Volume 586, Issue 1, pp (2003)  Gould, A., Applications of Microlensing to Stellar Astrophysics, The Publications of the Astronomical Society of the Pacific, Volume 113, Issue 786, pp (2001)  Graff, D. S., and Gaudi, B. S., Direct Detection of Large Close-in Planets around the Source Stars of Caustic-crossing Microlensing Events, The Astrophysical Journal, Volume 538, Issue 2, pp. L133-L136 (2000)  SIM homepage:  The animations were created by Scott Gaudi