Extended Data Fig. 1: The observational properties of the Phoenix member stars.
From: The tidal remnant of an unusually metal-poor globular cluster
a, The on-sky distribution of all stars observed in the 2dF fields targeting the Phoenix stream. The overall footprint is a series of circular 2dF pointings. R.A., right ascension; Dec., declination. b, Radial velocity in the Galactic standard of rest (RVGSR) versus stream longitude (ϕ1) for Phoenix stars selected on the basis of proper motion, photometry and the mixture model. On the basis of the approximately linear correlation between RVGSR and ϕ1, we select Phoenix stream members from the region between the dashed lines ((1.02ϕ1 – 60.7) km s−1 < RVGSR < (1.02ϕ1 – 42.7) km s−1), which effectively excludes non-members (shown as small pink circles). c, The colour–magnitude diagram of stars selected as members of the Phoenix stream. Over-plotted are PADOVA isochrones41 with [Fe/H] = −2.9 to [Fe/H] = −2.0 (from blue to red), m − M = 16.4 (ref. 9, where m − M is the distance modulus, m is the apparent magnitude and M is the absolute magnitude) and log10[age (Gyr)] = 10.05. In all panels, the stars we identify as members of the Phoenix stream are represented by larger circles; those with high signal-to-noise ratio are colour-coded by their metallicity, others are grey. The four orange squares indicate the BHB and RR Lyrae stars, metallicities of which cannot be measured using the method used here.
