While OGLE data taken during earlier stages of the event OGLE 2005-BLG-153 / MOA 2005-BLG-23 already revealed anomalous behaviour by showing a further rise after the light curve had already flattened, PLANET data collected with the Canopus 1.0m near Hobart (Tasmania) suggest a caustic entry, as announced in PLANET anomaly alert 2005 #7 (issued 3-Jul, 18:15 UT).
Further observations with the Danish 1.54m at ESO LaSilla as well as OGLE data support this interpretation and show the suspected caustic entry to be still in progress, as reported in PLANET anomaly update 2005 #7-1 (issued 4-Jul, 11:50 UT). A fold-caustic approximation suggests the caustic entry to have started around HJD=24535564.97 (3-Jul, 11:10 UT) and to last about 1.8 days.
The long duration together with the bright target makes this event another excellent candidate for studying a stellar atmosphere. For providing such information, both the beginning and the end of a caustic passage (entry or exit), corresponding to either the leading or the trailing limb passing, are of particular value. From the actual data, the source is expected to complete its caustic entry by HJD=2453556.8 (5-Jul, 6:30 UT), provided the model approximations are valid.
PLANET anomaly update 2005 #7-2 (issued 8-Jul, 9:15 UT) reports an observed rise to an expected caustic peak with the source likely to start exiting within the next 24 hours.
As announced in PLANET anomaly update 2005 #7-3 (issued 9-Jul, 12:15 UT), continued monitoring reveals that the anticipated caustic exit peak has been passed around HJD=2453460.4 (8-Jul, 21:30 UT), and the source is expected to leave to caustic at HJD=2453561.72 +/- 0.03 (10-Jul, 5:15 UT) after it needed (1.63 +/- 0.03) days for crossing it.
Subsequent data we have collected confirm that the trailing limb of the source star left the caustic at HJD=2453561.724 +/- 0.002, as reported in PLANET anomaly update 2005 #7-4 (issued 10-Jul, 07:25 UT).
The reported features can be seen in our light curve showing the latest data.