The PLANET collaboration has detected an anomaly in the on-going microlensing event OGLE-1999-BUL-25 (also MACHO 99-BLG-35). PLANET observations near JD - 2450000 = 1342 indicate that the event brightened by 2.7 magnitudes in 17 hours, swiftly falling by more than 2 magnitudes with a curvature that is suggestive of a caustic crossing. An anomaly alert was issued.
RA (J2000): 17:59:41.14
Dec (J2000): -28:47:18.4
The baseline I magnitude reported by the OGLE team is 18.5.
PLANET continues to observe this event. Observations by others, both photometric and spectrographic, are encouraged. A postscript finding chart can be downloaded here.
Caustic crossing events can be used to measure source resolution effects, which can allow the determination of the relative proper motion of the lens and, in special circumstances, the limb-darkening of the source star. High magnification events, are especially likely to betray the presence of possible planets orbiting the lens.
Finding charts and future updated information can be found on the PLANET web site at http://planet.iap.fr.
OGLE information on this event can be found at the OGLE alert web page at: http://www.astrouw.edu.pl/~ftp/ogle/ogle2/ews/bul-25.html.
MACHO information on this event can be found at the MACHO alert web page at: ftp://darkstar.astro.washington.edu/macho/Alert/99-BLG-35