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We present optical and infrared spectroscopy of the Ðrst 2 months of evolution of the Type II supernova SN 1999em. We combine these data with high-quality optical/infrared photometry beginning only 3 days after shock breakout, in order to study the performance of the "" expanding photosphere method ÏÏ (EPM) in the determination of distances. With this purpose, we develop a technique to measure accurate photospheric velocities by cross-correlating observed and model spectra. The application of this technique to SN 1999em shows that we can reach an average uncertainty of 11% in velocity from an individual spectrum. Our analysis shows that EPM is quite robust to the e †ects of dust. In particular, the distances derived from the V I Ðlters change by only 7% when the adopted visual extinction in the host galaxy is varied by 0.45 mag. The superb time sampling of the BV IZJHK light curves of SN 1999em permits us to study the internal consistency of EPM and test the dilution factors computed from atmosphere models for Type II plateau supernovae. We Ðnd that, in the Ðrst week since explosion, the EPM distances are up to 50% lower than the average, possibly because of the presence of circumstellar material. Over the following 65 days, on the other hand, our tests lend strong credence to the atmosphere models, and conÐrm previous claims that EPM can produce consistent distances without having to craft speciÐc models to each supernova. This is particularly true for the V I Ðlters, which yield dis- tances with an internal consistency of 4%. From the whole set of BV IZJHK photometry, we obtain an average distance of 7.5^0.5 Mpc, where the quoted uncertainty (7%) is a conservative estimate of the internal precision of the method obtained from the analysis of the Ðrst 70 days of the supernova evolution.

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We have embarked on a project, under the aegis of the Nearby Stars (NStars)/ Space Interferometry Mission Preparatory Science Program to obtain spectra, spectral types, and, where feasible, basic physical parameters for the 3600 dwarf and giant stars earlier than M0 within 40 parsecs of the sun. In this paper we report on the results of this project for the first 664 stars in the northern hemisphere. These results include precise, homogeneous spectral types, basic physical parameters (including the effective temperature, surface gravity and the overall metallicity, [M/H]) and measures of the chromospheric activity of our program stars. Observed and derived data presented in this paper are also available on the project's website http://stellar.phys.appstate.edu/.

We observed 69 A3YF8 main-sequence binary star systems using the Multiband Imaging Photometer for Spitzer on board the Spitzer Space Telescope. We find emission significantly in excess of predicted photospheric flux levels for 9 þ4 À3 % and 40 þ7 À6 % of these systems at 24 and 70 m, respectively. Twenty-two systems total have excess emission, including four systems that show excess emission at both wavelengths. A very large fraction (nearly 60%) of observed binary systems with small (<3 AU ) separations have excess thermal emission. We interpret the observed infrared excesses as thermal emission from dust produced by collisions in planetesimal belts. The incidence of debris disks around main-sequence A3YF8 binaries is marginally higher than that for single old AFGK stars. Whatever combination of nature (birth conditions of binary systems) and nurture (interactions between the two stars) drives the evolution of debris disks in binary systems, it is clear that planetesimal formation is not inhibited to any great degree. We model these dust disks through fitting the spectral energy distributions and derive typical dust temperatures in the range 100Y200 K and typical fractional luminosities around 10 À5, with both parameters similar to other Spitzer-discovered debris disks. Our calculated dust temperatures suggest that about half the excesses we observe are derived from circumbinary planetesimal belts and around one-third of the excesses clearly suggest circumstellar material. Three systems with excesses have dust in dynamically unstable regions, and we discuss possible scenarios for the origin of this short-lived dust.