We present a detailed discussion of our new 3D numerical models for the accretion of stellar winds on to Sgr A ^ { * } .
In our most sophisticated models , we put stellar wind sources on realistic orbits around Sgr A ^ { * } , we include recently discovered ‘ slow ’ winds ( v _ { w } \sim 300 km s ^ { -1 } ) , and we account for optically thin radiative cooling .
We test our approach by first modelling only one phase ‘ fast ’ stellar winds ( v _ { w } \sim 1000 km s ^ { -1 } ) .
For stellar wind sources fixed in space , the accretion rate is of the order of \dot { M } \simeq 10 ^ { -5 } { { M } _ { \odot } } yr ^ { -1 } , fluctuates by \lower 2.15 pt \hbox { $ \buildrel < \over { \sim } $ } 10 % , and is in a good agreement with previous models .
In contrast , \dot { M } decreases by an order of magnitude for wind sources following circular orbits , and fluctuates by \sim 50 % .
Then we allow a fraction of stars to produce slow winds .
Much of these winds cool radiatively after being shocked , forming cold clumps and filaments immersed into the X-ray emitting gas .
We investigate two orbital configurations for the stars in this scenario , an isotropic distribution and two rotating discs with perpendicular orientation .
The morphology of cold gas is quite sensitive to the orbital distribution of the stars .
In both cases , however , most of the accreted gas is hot , producing a quasi steady ‘ floor ’ in the accretion rate , of the order of \sim 3 \times 10 ^ { -6 } { { M } _ { \odot } } yr ^ { -1 } , consistent with the values deduced from Chandra observations .
The cold gas accretes in intermittent , short but powerful accretion episodes which may give rise to large amplitude variability in the luminosity of Sgr A ^ { * } on time scales of tens to hundreds of years .
The circularisation radii for the flows are about 10 ^ { 3 } and 10 ^ { 4 } Schwarzschild radii , for the one and two-phase wind simulations , respectively , never forming the quasi-spherical accretion flows suggested in some previous work .
Our work suggests that , averaged over time scales of hundreds to thousands of years , the radiative and mechanical luminosity of Sgr A ^ { * } may be substantially higher than it is in its current state .
Further improvements of the wind accretion modelling of Sgr A ^ { * } will rely on improved observational constraints for the wind velocities , mass loss rates and stellar orbits .