ANOMALY ALERT: Multiple Lens Microlensing in MB-97-28

First posted: 15-June-1997
Last update: 24-June-1997

The PLANET collaboration has detected an anomaly in the on-going microlensing event MB-97-28 (MACHO 97-BLG-28). After a smooth rise, the source star exhibited rapid and dramatic departures from a simple point source-point lens model. The anomaly is suggestive of caustic structure due to a multiple lens crossing an extended source at JD - 2450449.0 = 165.5 +/- 0.1 days, at which time the source was measured to be magnified by A ~ 13. Continued PLANET observations indicate that as of JD - 2450449.0 = 166.9, the event has fallen to A ~ 4, giving it an approximate R magnitude of 15.4. The anomaly at JD - 2450449.0 = 165.5 appears to be over, but future behavior remains uncertain. PLANET has detected evidence for source resolution effects at the crossing.

Event:                 MB-97-28
RA (J2000):         18:00:33.8
Dec (J2000)       -28:01:10

Additional observations, both photometric and spectrographic, are encouraged. Finding charts with PLANET-selected reference stars and updated information for this event can be found on this PLANET web site.

Below are two images of the source star of MB-97-28 imaged at LaSilla before (left) and during (right) the first caustic crossing. The images subtend about 1 arminute on a side.
The star brightened by more than a factor 5 in 7 days due to microlensing by an unseen foreground multiple lens. North is up, East is to the left.

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