The accretion of hydrogen-rich matter onto C/O and O/Ne white dwarfs in binary systems leads to unstable thermonuclear ignition of the accreted envelope , triggering a convective thermonuclear runaway and a subsequent classical , recurrent , or symbiotic nova .
Prompted by uncertainties in the composition at the base of the accreted envelope at the onset of convection , as well as the range of abundances detected in nova ejecta , we examine the effects of varying the composition of the accreted material .
For high accretion rates and carbon mass fractions < 2 \times 10 ^ { -3 } , we find that carbon , which is usually assumed to trigger the runaway via proton captures , is instead depleted and converted to ^ { 14 } N. Additionally , we quantify the importance of ^ { 3 } He , finding that convection is triggered by ^ { 3 } He + ^ { 3 } He reactions for ^ { 3 } He mass fractions > 2 \times 10 ^ { -3 } .
These different triggering mechanisms , which occur for critical abundances relevant to many nova systems , alter the amount of mass that is accreted prior to a nova , causing the nova rate to depend on accreted composition .
Upcoming deep optical surveys such as Pan-STARRS-1 , Pan-STARRS-4 , and the Large Synoptic Survey Telescope may allow us to detect the dependence of nova rates on accreted composition .
Furthermore , the burning and depletion of ^ { 3 } He with a mass fraction of 10 ^ { -3 } , which is lower than necessary for triggering convection , still has an observable effect , resulting in a pre-outburst brightening in disk quiescence to > L _ { \odot } and an increase in effective temperature to 6.5 \times 10 ^ { 4 } K for a 1.0 M _ { \odot } white dwarf accreting at 10 ^ { -8 } M _ { \odot } { yr } ^ { -1 } .