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We present ultraviolet (UV) and optical photometry and spectra of the1999aa-like supernova (SN) iPTF14bdn. The UV data were observed using the SwiftUltraviolet/Optical Telescope (UVOT) and constitute the first UV spectralseries of a 1999aa-like SN. From the photometry we measure $\Delta m_{15}({\itB})\,=\,0.84 \pm0.05$ mag and blue UV colors at epochs earlier than $-5$ days.The spectra show that the early-time blue colors are the result of lessabsorption between $2800 - 3200 \,\AA~$ than is present in normal SNe Ia. Usingmodel spectra fits of the data at $-10 $ and $+10 $ days, we identify theorigin of this spectral feature to be a temperature effect in which doublyionized iron group elements create an opacity 'window'. We determine that thedetection of high temperatures and large quantities of iron group elements atearly epochs imply the mixing of a high Ni mass into the outer layers of the SNejecta. We also identify the source of the I-band secondary maximum iniPTF14bdn to be the decay of Fe III to Fe II, as is seen in normal SNe Ia.

The 1999aa-like Type Ia Supernova iPTF14bdn in the Ultraviolet and Optical