We present the results of an intensive ground-based spectrophotometric monitoring campaign of the Seyfert galaxy NGC 4151 for a period of over two months, with a typical temporal resolution of one day. Light curves for four optical continuum bands and the Hα and Hβ emission lines are given. During the monitoring period, the continuum at 6925 Å varied by ∼17% while the continuum at 4600 Å varied by ∼35%, with larger variations in the near UV. The wavelength dependence of the variation amplitude also extends into the far UV. The dependence in the 2700−7200 Å range can be explained by the different relative starlight contributions at different wavelengths, but the large variability at 1275 Å cannot be explained in this way. The continuum variability timescale is of order 13 days and is similar at all optical wavelength bands. No evidence for a time lag between the optical continuum and the UV continuum and emission lines was found. The Hα emission line flux varied by about 12% with a gradual rise throughout the campaign. Its cross correlation with the continuum light curve gives a lag of 0 − 2 days. The variations in the Hβ emission line flux are about 30% and lag the continuum by 0−3 days. This is in contrast to past results where a time lag of 9±2 days was found for both emission lines. This may be due to a different variability timescale of the ionizing continuum, or to a real change in the BLR gas distribution in the 5.5 years interval between the two campaigns.

drive the ultraviolet/optical variations. However, the medium energy X-ray NVA is 2-4 times that in the ultraviolet, and the single-epoch, absorption-corrected X-ray/γ-ray luminosity is only about 1/3 that of the ultraviolet/optical/infrared, suggesting that at most ∼1/3 of the total low-energy flux could be reprocessed high-energy emission.The strong wavelength dependence of the ultraviolet NVAs is consistent with an origin in an accretion disk, with the variable emission coming from the hotter inner regions and non-variable emission from the cooler outer regions. These data, when combined with the results of disk fits, indicate a boundary between these regions near a radius of order R ≈ 0.07 lt-day. No interband lag would be expected as reprocessing (and thus propagation between regions) need not occur, and the orbital time scale of ∼1 day is consistent with the observed variability time scale. However, such a model does not immediately explain the good correlation between ultraviolet and X-ray variations.

We present analysis of MACHO Alert 95-30, a dramatic gravitational microlensing event towards the Galactic bulge whose peak magnification departs significantly from the standard point-source microlensing model. Alert 95-30 was observed in real-time by the Global Microlensing Alert Network (GMAN), which obtained densely sampled photometric and spectroscopic data throughout the event. We interpret the light-curve "fine structure" as indicating transit of the lens across the extended face of the source star. This signifies resolution of a star several kpc distant.We find a lens angular impact parameter θ min /θ source = 0.715 ± 0.003. This information, along with the radius and distance of the source, provides an additional constraint on the lensing system. Spectroscopic and photometric data indicate the source is an M4 III star of radius 61 ± 12R ⊙ , located on the far side of the bulge at ∼ 9 kpc. We derive a lens angular velocity, relative to the source, of 21.5 ± 4.9 km s −1 kpc −1 , where the error is dominated by uncertainty in the source radius. Likelihood analysis yields a median lens mass of 0.67 +2.53 −0.46 M ⊙ , located with 80% probability in the Galactic bulge at a distance of 6.93 +1.56 −2.25 kpc. If the lens is a main-sequence star, we can include constraints on the lens luminosity. This modifies our estimates to M lens = 0.53 +0.52 −0.35 M ⊙ and D lens = 6.57 +0.99 −2.25 kpc. Spectra taken during the event show that the absorption line equivalent widths of Hα and the TiO bands near 6700Å vary, as predicted for microlensing of an extended source. This is most likely due to center-to-limb variation in the stellar spectral lines. The observed spectral changes further support our microlensing interpretation. These data demonstrate the feasibility of using microlensing limb crossings as a tool to probe stellar atmospheres directly.Subject headings: dark matter -gravitational lensing -stars: low-mass, brown dwarfsstars: late-type -stars: atmospheres Table 4. Photometry of the source star in MACHO 95-30Observed Extinction Dereddened Abs Mag, 8 kpc Abs Mag, 9 kpc V = 16.21 A V = 1.35 V 0 = 14.86 M V = +0.34 M V = +0.59 K = 9.98 A K = 0.15 K 0 = 9.83 M K = −4.69 M K = −4.45 V − R = 1.39 E(V − R) = 0.34 V − R 0 = 1.05 J − K = 1.12 E(J − K) = 0.23 J − K 0 = 0.89 H − K = 0.26 E(H − K) = 0.08 H − K 0 = 0.18 V − K = 6.23 E(V − K) = 1.21 V − K 0 = 5.03 Bolometric BC K = −2.7 ± 0.1 M bol = −2.0 M bol = −2.25

We present the lightcurves of 21 gravitational microlensing events from the first six years of the MACHO Project gravitational microlensing survey which are likely examples of lensing by binary systems. These events were manually selected from a total sample of ~350 candidate microlensing events which were either detected by the MACHO Alert System or discovered through retrospective analyses of the MACHO database. At least 14 of these 21 events exhibit strong (caustic) features, and 4 of the events are well fit with lensing by large mass ratio (brown dwarf or planetary) systems, although these fits are not necessarily unique. The total binary event rate is roughly consistent with predictions based upon our knowledge of the properties of binary stars, but a precise comparison cannot be made without a determination of our binary lens event detection efficiency. Towards the Galactic bulge, we find a ratio of caustic crossing to non-caustic crossing binary lensing events of 12:4, excluding one event for which we present 2 fits. This suggests significant incompleteness in our ability to detect and characterize non-caustic crossing binary lensing. The distribution of mass ratios, N(q), for these binary lenses appears relatively flat. We are also able to reliably measure source-face crossing times in 4 of the bulge caustic crossing events, and recover from them a distribution of lens proper motions, masses, and distances consistent with a population of Galactic bulge lenses at a distance of 7 +/- 1 kpc. This analysis yields 2 systems with companions of ~0.05 M_sun.Comment: 83 pages, including 5 tables and 48 figures; submitted to The Astrophysical Journal. Data will soon be available at http://wwwmacho.mcmaster.ca/ and http://wwwmacho.anu.edu.au

We present 20, 6, 3.6, and 2 cm Very Large Array maps and continuum-free Ha images of nine WolfRayet galaxies. The radio maps were made with high spatial resolution to reject extended emission and to emphasize the star formation regions. The ratio of Ha to radio is at least a factor of 10 lower than predicted, indicating that the radio emission is from highly obscured sources. We map the radio spectral index, a across each galaxy. In all the sample galaxies except one, the radio spectrum is much (S l P la), Ñatter than in spiral starburst galaxies, suggesting that free-free emission is more dominant in the dwarfs and that these are very young starbursts that have produced few supernovae. In many of the galaxies, there are regions where the spectrum rises from 6 to 2 cm. This requires that the radio emission be optically thick at wavelengths as short as 2 cm. In these optically thick regions, the emission measure, electron density, and ionizing Ñuxes must be very high, and they are probably the youngest parts of the starburst. The deduced ionization of these sources implies stellar content of hundreds to many thousands of O stars, which means that they may be responsible for a signiÐcant fraction of the total infrared luminosities of the galaxies. We discuss what these sources imply for the history and evolution of the starburst in each galaxy.