All Quiet in Globular Clusters

Cataclysmic Variables (CVs) should be present in large numbers in GlobularClusters (GCs). Numerous low-luminosity X-ray sources identified over the pastfew years as candidate CVs in GCs support this notion. Yet, very few"cataclysms," the characteristic feature of this class of objects in the field,have been observed in GCs. We address this discrepancy here, within theframework of the standard Disk Instability Model for CV outbursts. We arguethat the paucity of outbursts in GCs is probably not a direct consequence ofthe donors' low metallicities. We present diagnostics based on outburstproperties allowing tests of the hypothesis that rare cataclysms are entirelydue to lower mass transfer rates in GCs relative to the field, and we argueagainst this explanation. Instead, we propose that a combination of low masstransfer rates (>~ 10^14-15 g/s) and moderately strong white dwarf magneticmoments (>~ 10^30 G cm^3) stabilize CV disks in GCs and thus prevent most ofthem from experiencing frequent outbursts. If it is so, rare cataclysms in GCswould signal important evolutionary differences between field and cluster CVs.Comment: 28 pages, 6 figures, accepted for publication in Ap