BACCHUS elemental abundances. Panel a: observed [X/H] and [Fe/H] abundance-density estimation (violin representation) of M 54 stars and the observed abundance ratios of newly identified N-rich stars. The extra-tidal star from M 54 and a field star are highlighted with a black open circle and diamond, respectively. Each violin indicates the median and limits of the distribution with horizontal lines. The lime and dark violet violin representation refer to the abundance ratios of 20 stars (this work) and 7 stars from Mészáros et al. (2020), respectively. Panels b–e: distributions of light- (C,N), α- (Mg, Si) and odd-Z (Al) elements in different abundance planes. In each panel, the planes [Al/Fe] – [Mg/Fe], [N/Fe]–[C/Fe], [Al/Fe]–[Si/Fe], [Si/Fe]–[Mg/Fe] are shown, respectively, for GCs from Mészáros et al. (2020). The black dotted line at [Al/Fe] = +0.3 indicates the separation of FG and SG stars as proposed in Mészáros et al. (2020). The distribution of M 54 stars (lime squares) analyzed in this work are overlaid. The black open circle and diamond refer to the extra-tidal and field N-rich star, respectively. The plotted error bars show the typical abundance uncertainties.