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We have measured stellar photometry from deep Cycle 7 Hubble SpaceTelescope/WFPC2 imaging of the dwarf irregular galaxy Sextans A. The imagingwas taken in three filters: F555W ($V$; 8 orbits), F814W ($I$; 16 orbits), andF656N (H$\alpha$; 1 orbit). Combining these data with Cycle 5 WFPC2observations provides nearly complete coverage of the optically visible portionof the galaxy. The Cycle 7 observations are nearly 2 magnitudes more sensitivethan the Cycle 5 observations, which provides unambiguous separation of thefaint blue helium burning stars (BHeB stars) from contaminant populations. Thedepth of the photometry allows us to compare recent star formation historiesrecovered from both the main sequence (MS) stars and the BHeB stars for thelast 300 Myr. The excellent agreement between these independent star formationrate (SFR) calculations is a resounding confirmation for the legitimacy ofusing the BHeB stars to calculate the recent SFR. Using the BHeB stars we havecalculated the global star formation history over the past 700 Myr. The historycalculated from the Cycle 7 data is remarkably identical to that calculatedfrom the Cycle 5 data, implying that both halves of the galaxy formed stars inconcert. We have also calculated the spatially resolved star formation history,combining the fields from the Cycle 5 and Cycle 7 data. Our interpretation ofthe pattern of star formation is that it is an orderly stochastic process.Comment: 27 pages, 14 figures, 2 mpeg movies, accepted in the Astronomical  Journa

Deep [ITAL]Hubble Space Telescope[/ITAL] Imaging of Sextans A. I. The Spatially Resolved Recent Star Formation History