Context : The reflection nebula NGC 7129 has long been known to be a site of recent star formation as evidenced , e.g. , by the presence of deeply embedded protostars and HH objects .
However , studies of the stellar population produced in the star formation process have remained rudimentary .
A major step forward was made with recent Spitzer imaging of the region .

Aims : This study represents the next step towards a systematic assessment of the pre-main sequence population in NGC 7129 .
Completeness of the pre-main sequence sample is necessary for studying key features that allow to understand the star forming process , such as disk evolution , dynamical evolution and mass function .
At a presumed age of \sim 3 Myr , NGC 7129 is in the critical range where disks around young stars disappear .

Methods : We make use of X-ray and IR imaging observations to identify the pre-main sequence stars in NGC 7129 .
We define a sample of Young Stellar Objects based on color-color diagrams composed from IR photometry between 1.6 and 8 \mu m , from 2 MASS and Spitzer , and based on X-ray detected sources from a Chandra observation .

Results : This sample is composed of 26 Class II and 25 Class III candidates .
It has been selected from infrared sources in the Chandra field ( 287 objects with photometry in all four Spitzer/IRAC bands , 811 objects with near-IR photometry ) and the 59 X-ray sources detected with Chandra .
The sample is estimated to be complete down to \sim 0.5 { M _ { \odot } } .
The most restricted and least biased sub-sample of pre-main sequence stars is composed of lightly absorbed ( A _ { V } < 5 mag ) stars in the cluster core .
This sample comprises 7 Class II and 14 Class III sources , it has a disk fraction of 33 ^ { +24 } _ { -19 } % , and a median X-ray luminosity of \log { L _ { x } } { [ erg / s ] } = 30.3 .

Conclusions : Despite the various uncertainties related to the sample selection , absorption , mass distribution , distance and , consequently , the computation of disk fraction and X-ray luminosities , the data yield consistent results .
In particular , we confirm the age of \sim 3 Myr for the NGC 7129 cluster .
The derived disk fraction is similar to that of \sigma Orionis , smaller than that of Cha I ( \sim 2 Myr ) , and larger than that of Upper Sco ( 5 Myr ) .
The X-ray luminosity function is similar to that of NGC 2264 ( 2 Myr ) but fainter than that of the Orion Nebula Cluster ( 1 Myr ) .
The pre-main sequence census should be further refined and extended with optical photometric and spectroscopic searches for cluster members .