Modifications to General Relativity typically introduce a scalar degree of freedom .
Experimental constraints require that the “ fifth ” force produced by this field must be screened in high density environments .
An important consequence of the screening mechanism is that the scalar charge of a spherically symmetric expanding or pulsating object , such as a supernova or variable star , is not conserved and monopole radiation can be emitted thereby .
We calculate the energy loss rate due to scalar monopole radiation in supernovae and variable stars for a generalized model of f ( R ) gravity in which the matter coupling strength \beta is allowed to be much larger than unity .
For models which become screened at the gravitational potential of our galaxy , monopole radiation constraints require \beta \lesssim 100 .