Identification of Exoplanet Host Star

This is a Hubble Space Telescope view of a small region of our galaxy where the host star to a gravitationally lensed planet (catalogued as OGLE-2003-BLG-235L/MOA-2003-BLG-53L) is located. The star is identified by the crosshatch at frame center. The planet was first identified in ground-based microlensing observations in July 2003. Gravitational microlensing happens when a foreground star-planet system slightly amplifies the light of a background star that momentarily aligns with it.

A blowup of the target (lower left) reveals the light of two stars: a foreground star and a background star superimposed on each other. The background star is the brighter, solar type star, and the foreground star is the fainter star. The motion of the foreground star, as it drifts past the more distant background star is apparent in the Hubble image taken in 2005, even though it is below Hubble's resolution. The light from each star is progressively more offset, year after year. This gives rise to a color difference effect because the foreground star turns out to be a different color from the background star. By observing the stars though a red and blue filter, astronomers were able to enhance the visibility of the offset. The relative offset is 0.7 milliarcseconds (the angular width of a dime seen 3,000 miles away) from the source star. The deduced positions of the two stars in 2005 are shown with red and blue crosshatches.

About the colours

These images are composites of many separate exposures made by the ACS instrument on the Hubble Space Telescope using several different filters. Three filters sample broad wavelength ranges, one isolates the light of hydrogen. The color results from assigning different hues (colors) to each monochromatic image. In this case, the assigned colors are: [Full Image:] Blue: F435W (B) Green: F555W (V) Red: F814W (I) [Detail Image:] Blue: F435W (B) Red: F814W (I)

About the data

This image was created from HST data from proposals 10426 I. Bond (Massey University), D. Bennett (University of Notre Dame), M. Jaroszynski (Warsaw University), B. Paczynski (Princeton University), N. Rattenbury (University of Manchester), A. Udalski (Warsaw University), and P. Yock (University of Auckland).

The science team comprises: D. Bennett (University of Notre Dame), J. Anderson (Rice University), I. Bond (Massey University, Auckland, New Zealand), A. Udalski (Warsaw University Observatory), and A. Gould (Ohio State University)