A prediction of the galaxy cluster cooling flow model is that as gas cools from the ambient cluster temperature , emission lines are produced in gas at subsequently decreasing temperatures .
Gas passing through 10 ^ { 5.5 } K emits in the lines of O vi \lambda \lambda 1032 , 1035 , and here we report a FUSE study of these lines in three cooling flow clusters , Abell 426 , Abell 1795 , and AWM 7 .
No emission was detected from AWM 7 , but O vi is detected from the centers of Abell 426 and Abell 1795 , and possibly to the south of the center in Abell 1795 , where X-ray and optical emission line filaments lie .
In Abell 426 , these line luminosities imply a cooling rate of 32 \pm 6 M _ { { \odot } { } } yr ^ { -1 } within the central r = 6.2 kpc region , while for Abell 1795 , the central cooling rate is 26 \pm 7 M _ { { \odot } { } } yr ^ { -1 } ( within r = 22 kpc ) , and about 42 \pm 9 M _ { { \odot } { } } yr ^ { -1 } including the southern pointing .

Including other studies , three of six clusters have O vi emission , and they also have star formation as well as emission lines from 10 ^ { 4 } K gas .
These observations are generally consistent with the cooling flow model but at a rate closer to 30 M _ { { \odot } { } } yr ^ { -1 } than originally suggested values of 10 ^ { 2 } –10 ^ { 3 } M _ { { \odot } { } } yr ^ { -1 } .