--------------------------------------------- PLANET ANOMALY UPDATE 2005 #0-5 (issued 25-May, 10:20 UT) --------------------------------------------- Caustic exit approaching / Further long caustic passage expected Dear Colleagues, PLANET data taken with the Perth 0.6m from HJD=2453513.0986 (22-May, 14:22 UT) to HJD=2453513.2982 (22-May, 19:09 UT) and from HJD=2453514.1307 (23-May, 15:08 UT) to HJD=2453514.3640 (23-May, 20:44 UT) reveal a stronger decrease in magnitude than our simple model predicted. However, a parallax-included model provides a reasonable fit to both the caustic peak region and the first peak. Although Perth data was not included (in a first fit), it matches the revised model prediction almost perfectly. This model predicts the source to exit the caustic near HJD=2453516.12 (25-May, 14:55 UT) and re-enter near HJD=2453520.73 (30-May, 5:30 UT) before finally exiting around HJD=2453530.56 (9-Jun, 1:26 UT). With the source moving under a small angle with respect to the caustic tangent, the epoch of caustic re-entry is difficult to estimate and therefore subject to refinement as further data has been obtained. A small shortcoming around the first peak should be resolved by lens orbital motion which has been found to play a smaller role than parallax from the data. However, this might also affect the future predicted behaviour a bit. The latest Danish point is strongly doubtful, thanks to the bright sky due to the moon. If this measurement is correct however, it would point to an earlier caustic exit, which could have already taken place. The coming long-lasting caustic passage of about 1.5 weeks duration will provide an unprecendented opportunity for resolving a stellar atmosphere, where current data already favour a linear limb-darkening coefficient of c ~ 0.62. The huge potential is linked to several favourable properties, namely the long event time-scale, the large angular source size as compared to the angular Einstein radius, the brightness of the source, the variety of caustic crossing angles, and the predictability. Photometric and spectroscopic follow-up observations are strongly encouraged. Our model lightcurve along with the data can be found on our webpage. Event: OGLE 2005-BLG-018 RA (J2000): 17:51:23.53 Dec (J2000): -29:39:27.8 The baseline I magnitude reported by the OGLE team is 15.448. For further information: PLANET: http://planet.iap.fr OGLE: http://www.astrouw.edu.pl/~ftp/ogle/ -------------- 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.