There is ample evidence in the Milky Way for globular cluster ( GC ) disruption .
Hence one may expect that also part of the Galactic halo field star population may once have formed in GCs .
We seek to quantify the fraction of halo stars donated by GCs by searching for stars that bear the unique chemical fingerprints typical for a subset of GC stars often dubbed as “ second-generation stars ” .
These are stars showing light element abundance anomalies such as a pronounced CN-band strength accompanied by weak CH-bands .
Based on this indicator , past studies have placed the fraction of halo stars with a GC origin between a few to up to 50 % .
Using low-resolution spectra from the most recent data release ( DR14 ) of the latest extension of the Sloan Digital Sky Survey ( SDSS-IV ) , we were able to identify 118 metal-poor ( -1.8 \leq [ Fe/H ] \leq - 1.3 ) CN-strong stars in a sample of 4470 halo giant stars out to \sim 50 kpc .
This increases the number of known halo stars with GC-like light-element abundances by a factor of two and results in an observed fraction of these stars of 2.6 \pm 0.2 % .
Using an updated formalism to account for the fraction of stars lost early on in the GCs ’ evolution we thus estimate the fraction of the Galactic halo that stems from disrupted clusters to be very low , at 11 \pm 1 % .
This number would represent the case that stars lost from GCs were entirely from the first generation and is thus merely an upper limit .
Our conclusions are sensitive to our assumptions of the mass lost early on from the first generation formed in the GCs , the ratio of first-to-second generation stars , and other GC parameters .
We carefully test the influence of varying these parameters on the final result and find that , under realistic scenarios , the above fraction depends on the main assumptions at less than 10 percentage points .
We further recover a flat trend in this fraction with Galactocentric radius , with a marginal indication of a rise beyond 30 kpc that could reflect the ex-situ origin of the outer halo as is also seen in other stellar tracers .