The Pristine survey -- XVII. The C-19 stream is dynamically hot and more
  extended than previously thought
  The C-19 stream is the most metal poor stellar system ever discovered, with a
mean metallicity $[Fe/H] = -3.38\pm0.06$. Its low metallicity dispersion
($\sigma_{\rm [Fe/H]}$ $<$ 0.18 at the 95\% confidence level) as well as
variations in sodium abundances strongly suggest a globular cluster origin. In
this work, we use VLT/UVES spectra of seven C-19 stars to derive more precise
velocity measurements for member stars, and to identify two new members with
radial velocities and metallicities consistent with the stream's properties.
One of these new member stars is located 30 $\deg$ away from the previously
identified body of C-19, implying that the stream is significantly more
extended than previously known and that more members likely await discovery. In
the main part of C-19, we measure a radial velocity dispersion $\sigma_v$ =
6.2$^{+2.0}_{-1.4}$ km s$^{-1}$ from nine members, and a stream width of
0.56$\deg\pm0.08\deg$, equivalent to $\sim$158 pc at a heliocentric distance of
18 kpc. These confirm that C-19 is comparatively hotter, dynamically, than
other known globular cluster streams and shares the properties of faint dwarf
galaxy streams. On the other hand, the variations in the Na abundances of the
three newly observed bright member stars, the variations in Mg and Al for two
of them, and the normal Ba abundance of the one star where it can be measured
provide further evidence for a globular cluster origin. The tension between the
dynamical and chemical properties of C-19 suggests that its progenitor
experienced a complex birth environment or disruption history.
