They are 2 Tristars that was recently bought by a hotel in Vegas.
These are ex Saudia royal flight -500 models, I understand they will be in service soon flying the high rollers from Vegas to the middle east.
If I remember correctly they will only have around 50 pax.
The -500 model has quite a bit of range.
The others are a bit range limited.
All are excellent wide body aircraft.
Last I heard ATA was either getting rid of the Tristar or slowly converting to DC-!0"s.