Astrophysical applications of gravitational

microlensing(II)By Shude Mao

Ziang Yan Department of Physics ,Tsinghua

Basics of GM: Lens Events

Fig1

Basics of GM: Light Curve

Fig.2 a standard light curve of GM

Basics of GM: Light Curve

Fig.3 The left pic. shows the process of a lens event. The pic. above is an example of light curve(Paczynski 1986)

Basics of GM: Critical Curves and Caustic

Fig.4 Critical curves and caustic in a binary system

Application of GM1.Detect the main composition in the galactic halo.

2.Detect the galactic structure. With analyzing the optical depth and event rate.3.Analyze the stellar atmosphere and bulge formation Microlensing can magnify the signal-to-noise ratio.4.Detect exoplanets

Application of GM: Detection of Exoplanets

The presence of the planet perturbs the image positions and magnifications

In fact it can create one or three extra images Fig.4

Application of GM: Detection of Exoplanets

Fig.5 OGLE-2005-BLG-390: A super-Earth (≈ 5.5M ) discovered by ⊕microlensing

Application of GM: Detection of Exoplanets

Fig.6 The first two-planet system discovered by Gaudi et al.

Fig.6Family Album of Microlensing Planets

Application of GM: Detection of Exoplanets

• About 20% of stars host Jupiter-mass planets (between 0.3 and 10Jupiter masses) while cool Neptunes (10 − 30M⊕) and super-Earths (5 − 10M⊕) are even more common: their abundances per star are close to 60%.(Cassan et al.)

• Free-floating planets may be common: ~ 1.8 per star

Fig.7

Application of GM: Galaxy Structure

From the detections of MACHOs by microlensing, it is concluded that only ≤2%of the halo could be MACHOs. While earlier research 20%.

Fig.8 Where are they looking?

Future of GM• There are still much problems unsolved in the calculation of GM. e.g.

The degenerate in the parallax events; how to distinguish exoplanet system with binary system; the number of critical curves and image numbers in a topological sense.• There are more and more collaborations participate in the detection

of GM like OGLE, MOA, SKYMAPPER and so on. Chinese scientists also make their distributions.

Thank you for listening!