Search for QSO Candidates in OGLE-II Data

摘要

A search for faint slowly variable objects was undertaken in the hope of finding QSO candidates behind the Small and Large Magellanic Clouds (SMC and LMC). This search used the optical variability properties of point sources from the Magellanic Cloud OGLE-II photometric data. Objects bluer than V - I = 0.9 mag and within 17 mag < I < 20.5 mag were studied. Robust variograms/structure functions have been computed for each time-series and only candidates showing a significantly increasing variability over longer time scales were selected. Several light curves were identified as having probable artifacts and were therefore removed. Stars showing signs of periodicity or small trends in their light curves were also removed and we are left with mostly either Be stars (γ Cas stars) or QSO candidates. We present a list of 25 slowly varying objects for SMC and 155 for LMC, out of 15000 and 53 000 variable objects respectively. Of these, about 15 objects for the SMC and 118 objects for the LMC are QSO candidates.