The deepestHubble Space Telescopefar-ultraviolet observations in the Large Magellanic Cloud

Abstract

We present a new analysis of the deepest pure-ultraviolet (UV) observations with the highest angular resolution ever performed. A set of 12 exposures with the Hubble Space Telescope (HST) WFPC2 and F160BW filter obtained in parallel observing mode, which cover ∼12 arcmin 2 in the Large Magellanic Cloud (LMC), north of the bar and in the ‘general field’ region of the LMC, contain stars with far-UV monochromatic magnitudes as faint as 22 mag. The 198 detected UV sources represent an accumulated exposure of 2 × 10 4 s and reveal stars as faint as m UV � 20 mag. We combine these observations with deep UBVI chargecoupled device (CCD) imaging of the same region reaching as faint as V � 26 mag, and reselect probable optical counterparts for the UV sources. After a two-stage search-and-analysis process, we detect robust counterparts for 129 stars. These are mostly upper main-sequence stars, from early B to early A spectral classes, with several F stars. We point out the lack of blue supergiants, which could have been easily detected in our survey. We measure a foreground extinction E(B − V ) � 0.08 mag by Galactic dust and a surface density of star formation rate twice the average Galactic value. These observations indicate that relatively recent star formation took place even off the bar of the LMC. Ke yw ords: stars: formation ‐ galaxies: individual: Large Magellanic Cloud ‐ galaxies: irregular ‐ galaxies: stellar content.