Sudden and short caustic exit in OGLE 2004-BLG-250

Sudden and short caustic exit in OGLE 2004-BLG-250

First posted on homepage: 17-Jun-2004
Moved to news archive: 21-Jun-2004

After data collected by the OGLE collaboration on the event OGLE 2004-BLG-250 indicated that the source entered a fold caustic between HJD-2450000 = 3152.9 (27-May, 9:30 UT) and HJD-2450000 = 3153.8 (28-May, 7:10 UT) and a decrease to a rather flat plateau region in the lightcurve was observed, PLANET anomaly alert 2004 #7 (issued 17-Jun, 9:40 UT) reported that PLANET data collected with the Danish 1.54m telescope at ESO LaSilla (Chile) showed a rise by about 0.6 mag between HJD-2450000 = 3168.8 (12-Jun, 7:10 UT) and HJD-2450000 = 3173.7 (17-Jun, 4:50 UT), leading to the prediction that the source center was to pass the caustic at HJD-2450000 = 3176.08 (-0.55/+0.62), i.e. 19-Jun, 14:00 UT (-13 h/+15 h).

As pointed out in PLANET anomaly update 2004 #7-1 (issued 17-Jun, 14:30 UT), OGLE data collected until 17-Jun, 8:36 UT together with PLANET data from the Danish 1.54m telescope at ESO LaSilla (Chile) until 17-Jun, 8:55 UT reveal that the expected caustic exit ended between HJD-2450000 = 3173.684 (17-Jun, 4:25 UT) and HJD-2450000 = 3173.747 (17-Jun, 5:55 UT). Despite the fact that most of the caustic exit was not covered by either of these data sets, the caustic passage duration can be restricted to be less than 16 hours. The previous estimate of the time of caustic exit was hampered by the wrong assumption that one of the data points was on the rise to the caustic exit peak, while it is now clear that it was observed during the decrease after the peak.

Unlike many other events, the caustic exit in OGLE 2004-BLG-250 was both short and sudden (i.e. it involved a short caustic rise time).

A regularly updated lightcurve, showing data from PLANET and OGLE, is available.

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