Multiple Lens Anomaly in MACHO 99-BLG-047

First posted: 4-Aug-1999
Updated: 18-Aug-1999

The PLANET collaboration has detected an anomaly in the on-going microlensing event MACHO 99-BLG-47. PLANET observations between JD - 2450000 = 1391 and 1396 indicate that the event underwent an increase in brightness of 0.7 magnitude that is inconsistent with single-source single-lens microlensing. The anomalous behaviour is likely due to multiple lens microlensing, including a possible caustic approach or crossing near JD - 2450000 = 1394.2. An electronic alert was issued and further photometric monitoring encouraged in order to characterize the nature of the binary and provide early warning for any possible future caustic events. The event is currently dropping slowly in brightness in a manner consistent with the source now being outside the anomalous magnification region.

Event:                  MB-99-047
RA (J2000):         18:30:49.4
Dec (J2000):     -14:10:53

The baseline V and R magnitudes reported by the MACHO team are 21.5 and 20.3, respectively, although MACHO also notes that the event may be significantly blended. A postscript finding chart can be downloaded here.

PLANET continues to observe this event.

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

MACHO information on this event can be found at the MACHO alert web page at:

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