We present extensive photometry at ultraviolet ( UV ) , optical , and near-infrared ( NIR ) wavelengths , as well as dense sampling of optical spectra , for the normal type Ia supernova ( SN Ia ) 2005cf .
The optical photometry , performed at eight different telescopes , shows a 1 \sigma scatter of \lesssim 0.03 mag after proper corrections for the instrument responses .
From the well-sampled light curves , we find that SN 2005cf reached a B -band maximum at 13.63 \pm 0.02 mag , with an observed luminosity decline rate \Delta m _ { 15 } ( B ) = 1.05 \pm 0.03 mag .
The correlations between the decline rate and various color indexes , recalibrated on the basis of an expanded SN Ia sample , yield a consistent estimate for the host-galaxy reddening of SN 2005cf , e.g. , E ( B - V ) _ { host } = 0.09 \pm 0.03 mag .
The UV photometry was obtained with the Hubble Space Telescope and the Swift Ultraviolet/Optical Telescope , and the results match each other to within 0.1–0.2 mag .
The UV light curves show similar evolution to the broadband U , with an exception in the 2000–2500 Å spectral range ( corresponding to the F220W/uvm2 filters ) , where the light curve appears broader and much fainter than that on either side ( likely owing to the intrinsic spectral evolution ) .
Combining the UV data with the ground-based optical and NIR data , we establish the generic UV-optical-NIR bolometric light curve for SN 2005cf and derive the bolometric corrections in the absence of UV and/or NIR data .
The overall spectral evolution of SN 2005cf is similar to that of a normal SN Ia , but with variety in the strength and profile of the main feature lines .
The spectra at early times displayed strong , high-velocity ( HV ) features in the Ca II H & K doublet and NIR triplet , which were distinctly detached from the photosphere ( v \approx 10 , 000 km s ^ { -1 } ) at a velocity ranging from 19,000 to 24,000 km s ^ { -1 } .
One interesting feature is the flat-bottomed absorption observed near 6000 Å in the earliest spectrum , which rapidly evolved into a triangular shape and then became a normal Si II \lambda 6355 absorption profile at about one week before maximum brightness .
This pre-maximum spectral evolution is perhaps due to the blending of the Si II \lambda 6355 at photospheric velocity and another HV absorption component ( e..g. , Si II shell at a velocity \sim 18,000 km s ^ { -1 } ) in the outer ejecta , and may be common in other normal SNe Ia .
The possible origin of the HV absorption features is briefly discussed .