Microlensing in Globular Clusters Margarita Safonova Ancient Greeks

Microlensing in Globular Clusters Margarita Safonova

Ancient Greeks knew that light travels in a straight line. . . Or you wouldn’t be able to cross the road! But when space is curved: The `straight’ path is also `curved’ The Castle on the Mall in Washington, D. C. , lensed by a `black hole’ “The Cheshire Cat”: CASSOWARY-2 Eyes: foreground ellipticals, face (arcs): b/g galaxies at z~0. 97 & z> 1. 4 Dark matter is not hidden to lensing! Refraction curves the path of the light because speed of light is reduced in matter

Effects of lensing v Shape distortions If the source is a disk of radius , the images will represent ellipses I 1 and I 2, squeezed along the axis connecting them and stretched in perpendicular direction. For example, the area of an ellipse is. Then, the areas of the images: I 2 . S D q. E I 1 b q 1 q 2

Effects of lensing v. Shape distortions Shapes of the images depend on the position of the source with respect to observer-lens line of sight

Effects of lensing v Magnification The sum of the brightness of two images, related to the brightness of the source is usually called magnification coefficient When impact parameter is small, the magnification coefficient is much more than unity. Perfect alignment of source, lens and observer `Einstein ring’ with radius and thickness

Microlensing When image separation is of the order of milliarcseconds, only total magnification is observable. Since everything is moving in the Universe, brightness changes – a light curve. ML was proposed in 1986 to discover dark matter in Galactic halo; In 1991 – to discover extrasolar planets; 1993 – first star-star microlensing observed; 2004 – first extrasolar planet discovered in Saggitarius.

I am looking for microlensing signals in globular clusters caused by • Intermediate-mass central black holes • Free-floating planets With thousands detected planets and billions estimated to exist in Galaxy, only 1 planet is found in a GC – cluster M 4

Observations of M 4 Apr-July 2011 WISE Observatory Tel Aviv, Israel Wide field imager 4 CCDs, each has 4 quadrants

Differential Differenceimaging; image ofquad 8 8 reference on 26/04/11 frame

Differential Imaging: transient source 23/06/11 24/06/11 25/06/11 Reference image subsection 1_1

Asteroid Kaminokinu from Aladin

Differential Imaging: variable source Quad 7

Differential Imaging: variable source 04 Apr. 2011 – 03 May 2011

Light curve and what to do next? This is a known field RR Lyrae ab phased with the ref. period P=0. 5225 days

New variables in quad 5 VC 1 VC 2

Search for ML continues….