Recent starbirth and starburst activity in nearby galaxies.

The ionizing starbirth activity in M101, M82, and NGC 1569 has been investigated via CCD imagery at H$\alpha$, R, I, and (SIII) bands. The three galaxies are compared with one another and with M51, M83, and the Milky Way in terms of their starbirth intensities, starbirth efficiencies, and possible starbirth histories. The globally-averaged starbirth intensities that are inferred from the extinction-corrected H$\alpha$ surface brightnesses vary by $\sim$3 orders of magnitude, with M101 and the Milky Way defining the low end and with M82 defining the high-intensity regime. The annular-averaged starbirth intensities correlate strongly with the H\sb2 surface densities and with the total gas surface densities, where near-linear relationships are obtained. Unusually high starbirth efficiencies and eruptive gaseous morphologies are evident in M82, NGC 1569, and NGC 5461--one of the supergiant HII region complexes in M101. Crude indices of the galaxies\u27 starbirth histories indicate temporally declining starbirth intensities in M101 and the Milky Way but currently bursting starbirth intensities in M82 and NGC 1569. In M101, annular-averaged photometry of the H$\alpha$ emission yields a much flatter galactocentric profile of surface brightness than that of the red-continuum starlight. The corresponding e-folding scale lengths are 9 and 3.3 kpc. respectively, thus implying significant differences between the galactocentric distributions of current-epoch massive star formation and past-averaged star formation. Moreover, the giant HII regions in M101 show significant variations in H$\alpha$ equivalent width as a function of both galactocentric radius and H$\alpha$ luminosity. These variations can be attributed to changes in the upper stellar mass limits of the ionizing clusters--M(upper) increasing in the outer galaxy, where the brighter HII regions are more numerous. The galactocentric variation in H$\alpha$ equivalent widths appears more closely related to the galaxy\u27s radial profile of differential rotation than to its monotonic gradient in O/H abundances. The ionizing stellar populations in early-type, late-type, and starburst galaxies are discussed in terms of these results

Windows in the Milky Way

The objectives were twofold: (1) to study the IRAS emission levels in the vicinity of Baade's Window and in other optically transparent regions near the Galactic Center; and (2) to study the IRAS emission levels along sightlines in the Milky Way that exhibit very little CO emission. Tests were attempted to see whether the optically transparent 'windows' near the Galactic center can be identified (as FIR-weak regions) in the IRAS data base; and if so, whether the CO weak regions found elsewhere in the Milky Way represent similarly FIR weak and thus optically transparent sightlines through the Galaxy. The CO weak regions were also targeted in an effort to study the diffuse intercloud dust and its warming by the interstellar radiation field

Orchestration of Starbirth Activity in Disk Galaxies: New Perspectives from Ultraviolet Imaging

Ultraviolet imaging of nearby disk galaxies reveals the star-forming activity in these systems with unprecedented clarity. UV images recently obtained with the Shuttle-borne Ultraviolet Imaging Telescope (UIT) reveal a remarkable variety of star-forming morphologies. The respective roles of tides, waves, and resonances in orchestrating the observed patterns of starbirth activity are discussed in terms of the extant UV data.Comment: Paper format (latex); length of paper (4); 2 encapsulated postscript figure files; uses AIP Press files aipproc.cls, aipproc.sty; Journal Reference: to be published in proceedings in "Star Formation, Near and Far", Proceedings of the 7th annual Astrophysics Conference in Maryland, Steve Holt, Lee G. Mundy, editor

How to Construct a Seasonal Index

4 pp., 5 graphsFor many crops, seasonality is often the dominant factor influencing prices within a single production period. This publication explains how to construct and use several kinds of seasonal indexes for crop marketing information