A B S T R A C TWe describe observations carried out by the MOA group of the Galactic bulge during 2000 that were designed to detect efficiently gravitational microlensing of faint stars in which the magnification is high and/or of short duration. These events are particularly useful for studies of extrasolar planets and faint stars. Approximately 17 deg 2 were monitored at a sampling rate of up to six times per night. The images were analysed in real time using a difference imaging technique. 20 microlensing candidates were detected, of which eight were alerted to the microlensing community whilst in progress. Approximately half of the candidates had high magnifications (*10), at least one had very high magnification (*50), and one exhibited a clear parallax effect. The details of these events are reported here, together with details of the on-line difference imaging technique. Some nova-like events were also observed and these are described, together with one asteroid.

We analyze the data of the gravitational microlensing survey carried out by the Microlensing Observations in Astrophysics (MOA) group during 2000 toward the Galactic bulge (GB). Our observations are designed to detect efficient high-magnification events with faint source stars and short-timescale events, by increasing the sampling rate up to $6 times per night and using Difference Image Analysis (DIA). We detect 28 microlensing candidates in 12 GB fields corresponding to 16 deg 2 . We use Monte Carlo simulations to estimate our microlensing event detection efficiency, where we construct the I-band extinction map of our GB fields in order to find dereddened magnitudes. We find a systematic bias and large uncertainty in the measured value of the timescale t E,out in our simulations. They are associated with blending and unresolved sources, and are allowed for in our measurements. We compute an optical depth ¼ 2:59 þ0:84 À0:64 Â 10 À6 toward the GB for events with timescales 0:3 < t E < 200 days. We consider disk-disk lensing, and obtain an optical depth bulge ¼ 3:36 þ1:11 À0:81 Â 10 À6 ½0:77=ð1 À f disk Þ for the bulge component assuming a 23% stellar contribution from disk stars. These observed optical depths are consistent with previous measurements by the MACHO and OGLE groups, and still higher than those predicted by existing Galactic models. We present the timescale distribution of the observed events, and find there are no significant short events of a few days, in spite of our high detection efficiency for short-timescale events down to t E $ 0:3 days. We find that half of all our detected events have high magnification (>10). These events are useful for studies of extrasolar planets.

We report on a global CCD time-series photometric campaign to decode the pulsations of the nucleus of the planetary nebula NGC 1501. The WC4 central star is an extremely hot, hydrogen-deficient, "O VI"-type object, with some spectroscopic characteristics similar to those of the pre-white-dwarf PG 1159−035 stars. NGC 1501 shows pulsational brightness variations of a few percent with numerous individual periods ranging from 19 to 87 minutes. The pulsation amplitudes and periods are highly variable, suggesting a complex pulsation spectrum that requires a long unbroken time series to resolve. To that end, we obtained CCD photometry of the central star over a two-week period in 1991 November, using a network of observatories around the globe. We obtained nearly continuous coverage over an interval of almost one week in the middle of the run. With this data set, we have identified 10 independent pulsation periods, ranging from 5235 s down to 1154 s. The pulsation modes changed amplitude significantly

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Presently scientists are working at Mt. John University Observatory in New Zealand using a technique known as gravitational microlensing to search for dark matter in our galaxy. This paper describes the current situation of the international collaboration known as MOA (Microlensing Observations in Astrophysics) that was formed by these scientists, together with future plans to improve the facilities. at Univ of Iowa-Law Library on May 27, 2015 http://ptps.oxfordjournals.org/ Downloaded from * ) Incidentally, MOA is also the name of a very large native bird which became extinct in New Zealand around two hundred years ago. at Univ of Iowa-Law Library on May 27, 2015 http://ptps.oxfordjournals.org/ Downloaded from * ) A second enhancement of the light curve was observed around 1084 days. This must be a variable star.