--------------------------------------------- PLANET ANOMALY ALERT 2004 #7 (issued 17-Jun, 9:40 UT) --------------------------------------------- OGLE 2004-BLG-250 probably approaching caustic exit Dear Colleagues, data collected by the OGLE collaboration on the event OGLE 2004-BLG-250 indicates 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). After a decrease to a rather flat plateau region in the lightcurve, 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). Unfavarouble observing conditions complicate the reduction of the data so that their proper interpretation requires some precaution. However, to the best of our knowledge, the observed rise lets us expect the source center to exit the caustic at HJD-2450000 = 3176.08 (-0.55/+0.62), i.e. 19-Jun, 14:00 UT (-13 h/+15 h), while the beginning of the caustic exit depends on the unknown crossing time of the source. Since the caustic exit will not happen very soon, a moderate sampling of the event should be sufficient at the moment, which should be increased once a very strong rise is observed (be prepared for this to happen). As more data becomes available, PLANET will try to update its predictions. A regularly updated lightcurve, showing data from PLANET, OGLE, and MicroFUN, can be viewed as 'http://planet.iap.fr/PublicCurves/OB04250p.gif'. Frequent photometric measurements during the course of the caustic exit can be used to obtain a measurement of the proper motion between lens and source and allow to measure the brightness profile of the source. A good coverage will reduce uncertainties in the properties of the binary lens system and in particular allow a lens mass measurement if parallax effects can be assessed properly. Event: OGLE 2004-BLG-250 RA (J2000): 18:07:20.51 Dec (J2000): -26:58:55.1 The baseline I magnitude reported by the OGLE team is 17.886. For more information, please consult: PLANET: http://planet.iap.fr/cuurentevents.html OGLE: http://www.astrouw.edu.pl/~ftp/ogle/ogle3/ews/blg-250.html MicroFUN: http://www.astronomy.ohio-state.edu/~microfun/Data/OB04250/ -------------- On behalf of the PLANET collaboration, Martin Dominik %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% If you prefer not to receive further PLANET Anomaly Alerts, please send an e-mail to planet@iap.fr.