Nathan Smith, Jon C. Mauerhan, Mansi M. Kasliwal, Adam J. Burgasser
We present low-resolution near-IR spectra of SN2009ip, taken immediately before, during, and just after its rapid brightening in late September/October 2012. The first epoch shows the same general spectral characteristics as the later epochs (smooth continuum, narrow H and HeI emission lines), but the continuum shape is subtantially redder than the later epochs. The continuum can be matched by reddening the peak-luminosity (epoch 3) spectrum by E(B-V)=1.0 mag, but the blue color seen in visual-wavelength spectra at the same time indicates that strong wavelength-dependent extinction by circumstellar dust is not the correct explanation. Instead, we favor the hypothesis that the redder color before the brightening arises from excess emission from hot 2000K CSM dust, heated in an infrared echo by radiation from the pre-SN outburst. The radius (120 AU) deduced from the dust temperature and observed luminosity of the transient, combined with the observed expansion speed in the precursor outbursts of SN2009ip, suggest an ejection 1.1 yr earlier. Thus, the observed pre-SN outbursts of this object were able to efficiently form dust into which the SN ejecta and radiation now propagate. This is consistent with the notion that the same pre-SN eruptions that generally give rise to SNe IIn also give rise to the dust needed for their commonly observed IR echoes. We also discuss some aspects of the IR line profiles, including HeI 10830.
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http://arxiv.org/abs/1303.0304
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