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.

0.1

0.30.5

Observable parameters:

1. Time of max (t0)

2. Time scale (tE)

3. Max magnification

PLANET data + fits

Paczynski curves:

…now add some sprinkles and fudge

tE

EROS BLG-2000-5tstar

The solution

Scale of source:Source star

characteristics:{color, magnitude

and spectrum}

Dsource

Rsource

θsource

Scale of lens:

sourcestartstart 2Relative proper

motion (lens-

source):

Et

EEEt

Astrometry: Rlens

Dlens

Mlens

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.”

Baseline 10 m

Wavelength range 0.4 - 0.9µm

Telescope Aperture 0.3 m diameter

Orbit Earth-trailing solar orbit

Mission Duration 5 years (launch in 2009)

Narrow Angle Astrometry 1 µas single measurement accuracy (goal)

Limiting Magnitude 20 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 Hα absorption line equivalent widths

Binary Lenses – brief recap

Choose the line of sight

Observation: EROS BLG-2000-5

(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

AUa

RRv

kpcDMM

Jupplanetkm

lenssolarlens

0467.0

27.1;60

7;3.0

sec

AUa

RRv

kpcDMM

Jupplanetkm

lenssolarlens

03.0

5.1;150

6;3.0

sec

AUa

RRv

kpcDMM

Jupplanetkm

lenssolarlens

03.0

5.1;150

6;3.0

sec

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)

Location (orbit)

Radius

Brightness

Atmosphere

Rings, etc.

follow-up no no

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-2000-5, Astronomy and Astrophysics, v.378, p.1014-1023 (2001)

An, J. H., First Microlens Mass Measurement: PLANET Photometry of EROS BLG-2000-5, The Astrophysical Journal, Volume 572, Issue 1, pp. 521-539 (2002)

Cassan, A., Probing the atmosphere of the bulge G5III star OGLE-2002-BUL-069 by analysis of microlense H alpha line, astro-ph/0401071 (2004)

Evans, N. W., The First Heroic Decade of Microlensing, astro-ph/0304252 (2002) Gaudi, B. S., Microlensing Searches for Extrasolar Planets: Current Status and Future Prospects,

astro-ph/0207533 (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. 463-499 (2002)

Gaudi, B. S. et al., Angular Radii of Stars via Microlensing, The Astrophysical Journal, Volume 586, Issue 1, pp. 451-463 (2003)

Gould, A., Applications of Microlensing to Stellar Astrophysics, The Publications of the Astronomical Society of the Pacific, Volume 113, Issue 786, pp. 903-915 (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: http://planetquest.jpl.nasa.gov/SIM/sim_index.html

The animations were created by Scott Gaudi