We present an extensive peakbagging effort on Kepler data of \sim 50 red giant stars in the open star cluster NGC 6819 .
By employing sophisticated pre-processing of the time series and Markov Chain Monte Carlo techniques we extracted individual frequencies , heights and linewidths for hundreds of oscillation modes .

We show that the ‘ average ’ asteroseismic parameter \delta \nu _ { 02 } , derived from these , can be used to distinguish the stellar evolutionary state between the red giant branch ( RGB ) stars and red clump ( RC ) stars .

Masses and radii are estimated using asteroseismic scaling relations , both empirically corrected to obtain self-consistency as well as agreement with independent measures of distance , and using updated theoretical corrections .
Remarkable agreement is found , allowing the evolutionary state of the giants to be determined exclusively from the empirical correction to the scaling relations .
We find a mean mass of the RGB stars and RC stars in NGC 6819 to be 1.61 \pm 0.02 \textup { M } _ { \odot } and 1.64 \pm 0.02 \textup { M } _ { \odot } , respectively .
The difference \Delta M = -0.03 \pm 0.01 \textup { M } _ { \odot } is almost insensitive to systematics , suggesting very little RGB mass loss , if any .

Stars that are outliers relative to the ensemble reveal overmassive members that likely evolved via mass-transfer in a blue straggler phase .
We suggest that KIC 4937011 , a low-mass Li-rich giant , is a cluster member in the RC phase that experienced very high mass-loss during its evolution .
Such over- and undermassive stars need to be considered when studying field giants , since the true age of such stars can not be known and there is currently no way to distinguish them from normal stars .