We have extracted PSF-fitted stellar photometry from near-ultraviolet , optical and near-infrared images , obtained with the Hubble Space Telescope , of the nearby ( D \approx 5.5 Mpc ) SBm galaxy NGC 1311 .
The ultraviolet and optical data reveal a population of hot main sequence stars with ages of 2–10 Myr .
We also find populations of blue supergiants with ages between 10 and 40 Myr and red supergiants with ages between 10 and 100 Myr .
Our near-infrared data shows evidence of star formation going back \sim 1 Gyr , in agreement with previous work .
Fits to isochrones indicate a metallicity of Z \approx 0.004 .
The ratio of blue to red supergiants is consistent with this metallicity .
This indicates that NGC 1311 follows the well-known luminosity-metallicity relation for late-type dwarf galaxies .
About half of the hot main sequence stars and blue supergiants are found in two regions in the inner part of NGC 1311 .
These two regions are each about 200 pc across , and thus have crossing times roughly equal to the 10 Myr age we find for the dominant young population .
The Luminosity Functions of the supergiants indicate a slowly rising star formation rate ( of \sim 10 ^ { -3 } M _ { \odot } ~ { } { yr } ^ { -1 } ) from \sim 100 Myr ago until \sim 15 Myr ago , followed by a strong enhancement ( to \sim 10 ^ { -2 } M _ { \odot } ~ { } { yr } ^ { -1 } ) at \sim 10 Myr ago .
We see no compelling evidence for gaps in the star-forming history of NGC 1311 over the last 100 Myr , and , with lower significance , none over the last Gyr .
This argues against a bursting mode , and in favor of a gasping or breathing mode for the recent star-formation history .