Context :

Aims : We study the properties of X-ray emitting plasma of MP Mus , an old classical T Tauri star .
We aim at checking whether an accretion process produces the observed X-ray emission and at deriving the accretion parameters and the characteristics of the shock-heated plasma .
We compare the properties of MP Mus with those of younger classical T Tauri stars to test whether age is related to the properties of the X-ray emission plasma .

Methods : XMM-Newton X-ray spectra allows us to measure plasma temperatures , abundances , and electron density .
In particular the density of cool plasma probes whether X-ray emission is produced by plasma heated in the accretion process .

Results : X-ray emission from MP Mus originates from high density cool plasma but a hot flaring component is also present , suggesting that both coronal magnetic activity and accretion contribute to the observed X-ray emission .
We find a Ne/O ratio similar to that observed in the much younger classical T Tauri star BP Tau .
From the soft part of the X-ray emission , mostly produced by plasma heated in the accretion shock , we derive a mass accretion rate of 5 \times 10 ^ { -11 } { M _ { \sun } yr ^ { -1 } } .

Conclusions :