We present a new , deep ( V \sim 26 ) study of the Galactic globular cluster NGC 2419 based on B,V,I time-series CCD photometry over about 10 years and extending beyond the cluster published tidal radius .
We have identified 101 variable stars of which 60 are new discoveries , doubling the known RR Lyrae stars and including 12 SX Phoenicis stars .
The average period of the RR Lyrae stars ( \left < Pab \right > =0.662 d , and \left < Pc \right > =0.366 d , for fundamental-mode - RRab - and first-overtone pulsators , respectively ) , and the position in the period-amplitude diagram both confirm that NGC 2419 is an Oosterhoff II cluster .
The average apparent magnitude of the RR Lyrae stars is { \langle V \rangle } =20.31 \pm 0.01 ( \sigma =0.06 , 67 stars ) and leads to the distance modulus \mu _ { 0 } =19.60 \pm 0.05 .
The Color-Magnitude Diagram , reaching about 2.6 mag below the cluster turn-off , does not show clear evidence of multiple stellar populations .
Cluster stars are found until r \sim 10.5 ^ { \prime } , and possibly as far as r \sim 15 ^ { \prime } , suggesting that the literature tidal radius might be underestimated .
No extra-tidal structures are clearly detected in the data .
NGC 2419 has many blue stragglers and a well populated horizontal branch extending from the RR Lyrae stars down to an extremely blue tail ending with the “ blue-hook ” , for the first time recognized in this cluster .
The red giant branch is narrow ruling out significant metallicity spreads .
Our results seem to disfavor the interpretation of NGC 2419 as either having an extragalactic origin or being the relict of a dwarf galaxy tidally disrupted by the Milky Way .