Regular collection of the background insures optimum photometric performance and increased {HEAD ~ baseline stability} of {TAIL ~ the system} 
of
Regular collection of the background insures optimum photometric performance and increased { HEAD ~ baseline stability } of { TAIL ~ the system }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL