Dwarf irregular galaxies are unique laboratories for studying the interaction between stars and the interstellar medium in low-mass environments. We present the highest spatial resolution observations to date of the neutral hydrogen content of the Local Group dwarf irregular galaxy WLM. We find that WLM's neutral hydrogen distribution is typical for a galaxy of its type and size and derive an H i mass of (6:3 AE 0:3) ; 10 7 M . In addition, we derive an H i extent for WLM of $30 0 , which is much less than the 45 0 extent found by Huchtmeier and coworkers. We show that the broken ring of high column density neutral hydrogen surrounding the center of WLM is likely the result of star formation propagating out from the center of the galaxy. The young stars and H emission in this galaxy are mostly correlated with the high column density neutral hydrogen. The gap in the central ring is the result of star formation in that region using up, blowing out, or ionizing all of the neutral hydrogen. Like many late-type galaxies, WLM's velocity field is asymmetric with the approaching (northern) side appearing to be warped and a steeper velocity gradient for the approaching side than for the receding side in the inner region of the galaxy. We derive a dynamical mass for WLM of 2:16 ; 10 9 M .

We present observations of the Galactic Cepheids Aql and Gem. Our observations are able to resolve the diameter changes associated with pulsation. This allows us to determine the distance to the Cepheids independent of photometric observations. We determine a distance to Aql of 320 AE 32 pc and a distance to Gem of 362 AE 38 pc. These observations allow us to calibrate surface brightness relations for use in extragalactic distance determination. They also provide a measurement of the mean diameter of these Cepheids, which is useful in constructing structural models of this class of star.

The Navy Prototype Optical Interferometer (NPOI) has been used to measure the angular diameters of 41 late-type giant and supergiant stars previously observed with the Mark III optical interferometer. Sixteen of these stars have published angular diameters based on model atmospheres (infrared Ñux method, IRFM). Comparison of these angular diameters shows that there are no systematic o †sets between any pair of data sets. Furthermore, the reported uncertainties in the angular diameters measured using both interferometers are consistent with the distribution of the di †erences in the diameters. The distribution of diameter di †erences between the interferometric and model atmosphere angular diameters are consistent with uncertainties in the IRFM diameters of 1.4%. Although large di †erences in angular diameter measurements are seen for three stars, the data are insufficient to determine whether these di †erences are due to problems with the observations or are due to temporal changes in the stellar diameters themselves.

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