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Session 101 - X-rays and X-ray Bursts.
Display session, Thursday, January 16
Recent COMPTEL observations revealed inhomogeneities in the spatial distribution of the Galactic ^26Al 1.809 MeV \gamma--ray emission, which reduces the required amount of ^26Al in a homogeneous background from \sim\,3 M_ødot (the value assuming all of the radiation is from a homogeneous background) to \sim\,1 M_ødot. Using recent nova population models and simulations of classical nova outbursts we reinvestigate the question of whether nova outbursts on oxygen--neon-- magnesium white dwarfs (ONeMg WDs) contribute significantly to the production of ^26Al in the Galaxy. We find an upper limit of \sim\,3 M_ødot for the amount of ^26Al produced by ONeMg novae in the Galaxy, if we adopt a value of 30% for the fraction f_ONeMg of novae in our models that are ONeMg novae and choose optimal models and parameter values. Uncertainties in both observations and theory do not allow us to quote a lower limit with any confidence at this time. Choosing models and parameter values that are more consistent with independent observational quantities gives an ^26Al production of \sim\,0.15 M_ødot, again for an assumed f_ONeMg of 30%. However, this value is dependent on our assumption of choosing the same amount of mixing between the underlying WD material and the accreted companion material for the entire population. If the mean amount of mixing in ONeMg novae is \sim a factor of 2 higher than the mean maximum amount of mixing for all novae, then we estimate that ONeMg novae can produce a sufficient amount of ^26Al (\sim\,1 M_ødot) to account for the entire diffuse background emission observed by COMPTEL. We explore to what extent ejecta abundances in well-studied novae support this possibility.
Program listing for Thursday