| The ESSENCE project is a 5-year observational program with the goal of discovering ∼ 200 type Ia supernovae and measuring their luminosity distances and redshifts in order to better constrain the equation of state of the cosmic Dark Energy. There exists today compelling evidence from at least three independent lines of investigation (type Ia supernovae, the cosmic microwave background, and large scale structure measurements) for the presence of "dark energy" in the universe, which in recent times has fueled an acceleration in the cosmic expansion rate. A number of explanations for the physics of the dark energy have been proposed, such as a cosmological constant or a scalar field ("quintessence"). By constraining the equation of state., we can begin to test these models. In particular, testing whether w = -1 allows us to determine whether or not a cosmological constant is consistent with observations.; In its first 3 years of operation at the Cerro Tololo 4m telescope in Chile, the project has successfully discovered 88 type Ia supernovae. We describe here the work done to establish the observing strategy for the survey and the software used to rapidly reduce nightly data and identify candidate supernovae. We also provide a detailed description of the photometric calibration of these data and the attendant sources of systematic error. We then describe the estimation of luminosity distances to these objects and present the cosmological analysis of these data. We give preliminary constraints on the dark energy equation of state parameter, w, and discuss sources of systematic error. |
