We have investigated the stellar content of Barnard 59 ( B59 ) , the most active star-forming core in the Pipe Nebula .
Using the SpeX spectrograph on the NASA Infrared Telescope Facility , we obtained moderate resolution , near-infrared ( NIR ) spectra for 20 candidate Young Stellar Objects ( YSOs ) in B59 and a representative sample of NIR and mid-IR bright sources distributed throughout the Pipe .
Measuring luminosity and temperature sensitive features in these spectra , we identified likely background giant stars and measured each star ’ s spectral type , extinction , and NIR continuum excess .

To measure B59 ’ s age , we place its candidate YSOs in the Hertzsprung-Russell ( HR ) diagram and compare their location to YSOs in several well studied star forming regions , as well as predictions of pre-main sequence evolutionary models .
We find that B59 is composed of late type ( K4-M6 ) low-mass ( 0.9–0.1 M _ { \odot } ) YSOs whose median stellar age is comparable to , if not slightly older than , that of YSOs within the \rho Oph , Taurus , and Chameleon star forming regions .
Deriving absolute age estimates from pre-main sequence models computed by D ’ Antona et al. , and accounting only for statistical uncertainties , we measure B59 ’ s median stellar age to be 2.6 \pm 0.8 Myrs .
Including potential systematic effects increases the error budget for B59 ’ s median ( DM98 ) stellar age to 2.6 ^ { +4.1 } _ { -2.6 } Myrs .
We also find that the relative age orderings implied by pre-main sequence evolutionary tracks depend on the range of stellar masses sampled , as model isochrones possess significantly different mass dependences .

The maximum likelihood median stellar age we measure for B59 , and the region ’ s observed gas properties , suggest that the B59 dense core has been stable against global collapse for roughly 6 dynamical timescales , and is actively forming stars with a star formation efficiency per dynamical time of \sim 6 \% .
While the \sim 150 % uncertainties associated with our age measurement propagate directly into these derived star formation timescales , the maximum likelihood values nonetheless agree well with recent star formation simulations that incorporate various forms of support against collapse , such as sub-critical magnetic fields , outflows , and radiative feedback from protostellar heating .