View
214
Download
0
Embed Size (px)
Citation preview
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:
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
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)
(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.
(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