We present the final results from a high sampling rate, multi-month, spectrophotometric reverberation mapping campaign undertaken to obtain either new or improved Hβ reverberation lag measurements for several relatively low-luminosity active galactic nuclei (AGNs). We have reliably measured the time delay between variations in the continuum and Hβ emission line in six local Seyfert 1 galaxies. These measurements are used to calculate the mass of the supermassive black hole at the center of each of these AGNs. We place our results in context to the most current calibration of the broad-line region (BLR) R BLR -L relationship, where our results remove outliers and reduce the scatter at the low-luminosity end of this relationship. We also present velocity-resolved Hβ time-delay measurements for our complete sample, though the clearest velocity-resolved kinematic signatures have already been published.

We have discovered a population of bright blue pointlike sources within 5 kpc of the nucleus of NGC 1275 using HST Planetary Camera observations. The typical object has Mv-12 to-14 (H 0 = 75 km s-1 Mpc-1); the brightest has M v-16. They are all blue, with V-R ;S 0.3. The color distribution and lack of excess Ha emission are consistent with nearly all being continuum sources. Many of the sources are unresolved even with the HST and consequently have sizes of ;S 15 pc. We suggest that these are young star clusters that will evolve to look like globular clusters. They are bluer than any clusters seen in the Milky Way or M87, and brighter than the blue clusters seen in the LMC. We derive ages of several hundred million years or less and corresponding masses of 10 5-10 8 1 0. The existence of these young clusters may be connected with a current or previous interaction with another galaxy, with the cooling flow in NGC 1275, or with some combination. Structure is detected in the underlying galaxy light that is suggestive of a merge between NGC 1275 and a second galaxy some 10 8 yr ago. If this merger triggered star formation, it would naturally account for the observed uniformity of cluster colors. Steady-state star formation in the x-ray cooling flow would imply a wider range in cluster age and color than is seen, unless the clusters disrupt. An interaction with the projected high-velocity, infalling system cannot explain the observations because this system has not yet reached the center of NGC 1275 where the clusters are concentrated, and because it has a total interaction time that is far too short for either the observed cluster lifetimes or the dynamical lifetime of structure in the galaxy. If the presence of recently formed protoglobulars around NGC 1275 is related to a previous merger, this would remove an important objection to the merger hypothesis for elliptical galaxy origins, provided that adequate gas is available in the merger for their formation.

The Juno microwave radiometer measured the thermal emission from Jupiter's atmosphere from the cloud tops at about 1 bar to as deep as a hundred bars of pressure during its first flyby over Jupiter (PJ1). The nadir brightness temperatures show that the Equatorial Zone is likely to be an ideal adiabat, which allows a determination of the deep ammonia abundance in the range 362−33+33 ppm. The combination of Markov chain Monte Carlo method and Tikhonov regularization is studied to invert Jupiter's global ammonia distribution assuming a prescribed temperature profile. The result shows (1) that ammonia is depleted globally down to 50–60 bars except within a few degrees of the equator, (2) the North Equatorial Belt is more depleted in ammonia than elsewhere, and (3) the ammonia concentration shows a slight inversion starting from about 7 bars to 2 bars. These results are robust regardless of the choice of water abundance.

We present Hubble Space Telescope WFPC2 images of elephant trunks in the H II region M16. There are three principle results of this study. First, the morphology and stratified ionization structure of the interface between the dense molecular material and the interior of the H II region is well understood in terms of photoionization of a photoevaporative flow. Photoionization models of an empirical density profile capture the essential features of the observations, including the extremely localized region of [S II] emission at the interface and the observed offset between emission peaks in lower and higher ionization lines. The details of this structure are found to be a sensitive function both of the density profile of the interface and of the shape of the ionizing continuum. Interpretation of the interaction of the photoevaporative flow with gas in the interior of the nebula supports the view that much of the emission from H II regions may arise in such flows. Photoionization of photoevaporative flows may provide a useful paradigm for interpreting a wide range of observations of H II regions. Second, we report the discovery of a population of small cometary globules that are being uncovered as the main bodies of the elephant trunks are dispersed. Several lines of evidence connect these globules to ongoing star formation, including the association of a number of globules with stellar objects seen in IR images of M16 or in the continuum HST images themselves. We refer to these structures as evaporating gaseous globules, or "EGGs." These appear to be the same type of object as the nebular condensations seen previously in M42. The primary difference between the two cases is that in M16 we are seeing the objects from the side, while in M42 the objects are seen more nearly face-on against the backdrop of the ionized face of the molecular cloud. We find that the "evaporating globule" interpretation naturally accounts for the properties of objects in both nebulae, while avoiding serious difficulties with the competing "evaporating disk" model previously applied to the objects in M42. More generally, we find that disk-like structures are relatively rare in either nebula. Third, the data indicate that photoevaporation may have uncovered many EGGs while the stellar objects in them were still accreting mass, thereby freezing the mass distribution of the protostars at an early stage in their evolution. We conclude that the masses of stars in the cluster environment in M16 are generally determined not by the onset of stellar winds, as in more isolated regions of star formation, but rather by disruption of the star forming environment by the nearby 0 stars.

We have obtained Ha and Paa emission-line images covering the central 3@È4@ of M51 using the WFPC2 and NICMOS instruments on the Hubble Space T elescope to study the high-mass stellar population. The pixels provide 4.6È9 pc resolution in M51, and the Ha/Paa line ratios are used to 0A .1È0A .2 obtain extinction estimates. A sample of 1373 Ha emission regions is cataloged using an automated and uniform measurement algorithm. Their sizes are typically 10È100 pc. The luminosity function for the Ha emission regions is obtained over the range to 2 ] 1039 ergs s~1. The luminosity function is L Ha \ 1036 Ðtted well by a power law with dN/d ln L P L~1.01. The power law is signiÐcantly truncated, and no regions were found with observed above 2 ] 1039 ergs s~1 (uncorrected for extinction). (The L Ha maximum seen in ground-based studies is approximately a factor of 5 higher, very likely because of the blending of multiple regions.) The extinctions derived here increase the maximum intrinsic luminosity to above 1040 ergs s~1. The logarithmically binned luminosity function is also somewhat steeper (a \ [1.01) than that found from ground-based imaging (a \ [0.5 to [0.8)Èprobably also a result of our resolving regions that were blended in the ground-based images. The two-point correlation function for the H II regions exhibits strong clustering on scales ¹2A, or 96 pc.To analyze the variations of H II region properties the galactic structure, the spiral arm areas vis-a`-vis were deÐned independently from millimeter-CO and optical continuum imaging. Although the arms constitute only 25% of the disk surface area, the arms contain 45% of the cataloged H II regions. The luminosity function is somewhat Ñatter in spiral arm regions than in the interarm areas ([0.72 to [0.95) ; however, this is very likely the result of increased blending of individual H II regions in the arms that have higher surface density. No signiÐcant di †erence is seen in the sizes and electron densities of the H II regions in spiral arm and interarm regions. For 209 regions that had º5 p detections in both Paa and Ha, the observed line ratios indicate visual extinctions in the range mag. The mean extinction A V \ 0È6 was mag (weighting each region equally), 2.4 mag (weighting each by the observed Ha A V \ 3.1 luminosity), and 3.0 mag (weighting by the extinction-corrected luminosity). On average, the observed Ha luminosities should be increased by a factor of D10, implying comparable increases in global OB star cluster luminosities and star formation rates. The full range of extinction-corrected Ha luminosities is between 1037 and 2 ] 1040 ergs s~1.The most luminous regions have sizes º100 pc, so it is very likely that they are blends of multiple regions. This is clear based on their sizes, which are much larger than the maximum diameter (¹50 pc) to which an H II region might conceivably expand within the D3 ] 106 yr lifetime of the OB stars. It is also consistent with the observed correlation (L P D2) between the measured luminosities and sizes of th...