Before revision:  The results obtained herein are remarkably different from those obtained in recent papers close-to-the-money option prices in that they aid in understanding how the behavior of implied volatility near expiry is affected by important model parameters , such as the leverage and vol vol parameters, that were not present in the aforementioned earlier results . Our simulation results also indicate that for parameter values of relevance in finance, the asymptotic expansions give a good fit for maturities up to one month   .
After revision:  The results obtained herein are remarkably different from those obtained in recent papers close-to-the-money option prices in that they aid in understanding how the behavior of implied volatility near expiry is affected by important model parameters , such as the leverage and vol-of-vol parameters. As intermediary results we obtain high-order expansions for at-the-money digital call option prices, which furthermore allow us to infer analogous results for the delta of at-the-money options. Simulation results indicate that our asymptotic expansions give a good fit for maturities up to one month .