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Using the Optical--NIR Spectral Energy Distributions To Search for the Evidence of Dust Formation of 66 Supernovae

In this paper, we searched for the dust formation evidence of 66 supernovae (SNe) by using the blackbody model and the blackbody plus dust {emission} model to fit their early$-$time optical$-$near infrared (NIR) spectral energy distributions (SEDs). We find that, while the blackbody model can fit most SEDs of the SNe in our sample, the model cannot fit the SEDs of some SNe, in which the SEDs of 2 SNe (SNe~2010bq and 2012ca) show NIR excesses which can be attributed to the emission from the heated dust. We use blackbody plus dust emission model to fit the SEDs showing NIR excesses, finding that both graphite and silicate dust models can fit the SEDs, and the graphite model get reasonable temperatures or better fits. Assuming that the dust is graphite, the best-fitting temperatures (masses) of the dust of the SNe~2010bq and 2012ca are $\sim 1300-1800$ K ($\sim 0.1-3.4 \times 10^{-4}$ M$_\odot$) and $\sim 600-1000$ K ($\sim 0.6-7.5 \times 10^{-3}$ M$_\odot$), respectively. We compare the vaporization radii and the blackbody radii of the dust shells of the 2 SNe with the upper limits of the ejecta radii of the SNe at the first epochs, and demonstrate that the NIR excesses of the SEDs of the 2 SNe might be caused by the pre-existing dust.