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Mrk 71 is a low metallicity (Z = 0.16 Z_sun) starburst region in the localdwarf galaxy NGC 2366, hosting two super star clusters (SSCs A and B), and isrecognized as a Green Pea (GP) analog with SSC A responsible for the GPproperties. We present STIS and FOS far-ultraviolet (FUV) spectra of theembedded SSC Mrk 71-A obtained with the Hubble Space Telescope (HST). The STISFUV spectrum shows the characteristic features of very massive stars (VMS,masses > 100 M_sun) and we derive an age of 1+/-1 Myr by comparison with theCharlot & Bruzual suite of spectral population synthesis models with upper masslimits of 300 and 600 M_sun. We compare the STIS spectrum with all known SSCspectra exhibiting VMS signatures: NGC 5253-5, R136a, NGC 3125-A1 and the z =2.37 Sunburst cluster. We find that the cluster mass-loss rates and windvelocities, as characterized by the C IV P Cygni profiles and the He IIemission line strengths, are very similar over Z = 0.16 to 0.4 Z_sun. Thisagrees with predictions that the optically thick winds of VMS will be enhancednear the Eddington limit and show little metallicity dependence. We find verystrong damped Lyman-alpha absorption with log N(H I) = 22.2 cm-2 associatedwith Mrk 71-A. We discuss the natal environment of this young SSC in terms ofradiatively-driven winds, catastrophic cooling and recent models where thecluster is surrounded by highly pressurized clouds with large neutral columns.

HST FUV Spectroscopy of Super Star Cluster A in the Green Pea Analog Mrk 71: Revealing the Presence of Very Massive Stars