Context : The gas- and dust dissipation processes in disks around young stars remain uncertain despite numerous studies .
At the distance of \sim 99–116 pc , HD141569A is one of the nearest HerbigAe stars that is surrounded by a tenuous disk , probably in transition between a massive primordial disk and a debris disk .
Atomic and molecular gases haves been found in the structured 5-Myr old HD141569A disk , making HD141569A the perfect object within which to directly study the gaseous atomic and molecular component .

Aims : We wish to constrain the gas and dust mass in the disk around HD141569A .

Methods : We observed the fine-structure lines of O I at 63 and 145 \mu m and the C II line at 157 \mu m with the PACS instrument onboard the Herschel Space Telescope as part of the open-time large programme GASPS .
We complemented the atomic line observations with archival Spitzer spectroscopic and photometric continuum data , a ground-based VLT-VISIR image at 8.6 \mu m , and ^ { 12 } CO fundamental ro-vibrational and pure rotational J =3–2 observations .
We simultaneously modeled the continuum emission and the line fluxes with the Monte Carlo radiative transfer code MCFOST and the thermo-chemical code ProDiMo to derive the disk gas- and dust properties assuming no dust settling .

Results : The models suggest that the oxygen lines are emitted from the inner disk around HD141569A , whereas the [ C II ] line emission is more extended .
The CO submillimeter flux is emitted mostly by the outer disk .
Simultaneous modeling of the photometric and line data using a realistic disk structure suggests a dust mass derived from grains with a radius smaller than 1 mm of \sim 2.1 \times 10 ^ { -7 } M _ { \odot } and from grains with a radius of up to 1 cm of 4.9 \times 10 ^ { -6 } M _ { \odot } .
We constrained the polycyclic aromatic hydrocarbons ( PAH ) mass to be between 2 \times 10 ^ { -11 } and 1.4 \times 10 ^ { -10 } M _ { \odot } assuming circumcircumcoronene ( C _ { 150 } H _ { 30 } ) as the representative PAH .
The associated PAH abundance relative to hydrogen is lower than those found in the interstellar medium ( 3 \times 10 ^ { -7 } ) by two to three orders of magnitude .
The disk around HD141569A is less massive in gas ( 2.5 to 4.9 \times 10 ^ { -4 } M _ { \odot } or 67 to 164 M _ { \oplus } ) and has a flat opening angle ( < 10 % ) .

Conclusions : We constrained simultaneously the silicate dust grain , PAH , and gas mass in a \sim 5-Myr old Herbig Ae disk .
The disk-averaged gas-to-dust-mass is most likely around 100 , which is the assumed value at the disk formation despite the uncertainties due to disagreements between the different gas tracers .
If the disk was originally massive , the gas and the dust would have dissipated at the same rate .