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We present an analysis of the second epoch HST WFC3 F110W near-Infrared (NIR)imaging data of the globular cluster M4. The new dataset suggests that one ofthe previously suggested four brown dwarf candidates in this cluster is indeeda high-probability cluster member. The position of this object in the NIRcolour magnitude diagrams (CMDs) is in the white dwarf/brown dwarf area. Thesource is too faint to be a low-mass main sequence star, but, according totheoretical considerations, also most likely somewhat too bright to be abona-fide brown dwarf. Since we know that the source is a cluster member, wedetermined a new optical magnitude estimate at the position the source shouldhave in the optical image. This new estimate places the source closer to thewhite dwarf sequence in the optical-NIR CMD and suggests that it might be avery cool (T_eff < 4500 K) white dwarf at the bottom of the white dwarf coolingsequence in M4, or a white dwarf/brown dwarf binary. We cannot entirely excludethe possibility that the source is a very massive, bright brown dwarf, or avery low-mass main sequence star, however, we conclude that we still have notconvincingly detected a brown dwarf in a globular cluster, but we expect to bevery close to the start of the brown dwarf cooling sequence in this cluster. Wealso note that the main sequence ends at F110W approx.22.5 mag in theproper-motion cleaned CMDs, where completeness is still high.

Hunting for Brown Dwarfs in the Globular Cluster M4: 2nd epoch HST NIR observations