NIR Spectrum of SN 2009ip on 2012 Sep 27.3 Confirms Interpretation as a Type IIn

ATel #4431; Adam Burgasser (UCSD), C. Nicholls (UCSD), Miriam Aberasturi (Centro de Astrobiologia)
on 27 Sep 2012; 19:58 UT
Credential Certification: Adam Burgasser (aburgasser@ucsd.edu)

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SN 2009ip has undergone significant spectral (Smith & Mauerhan, ATel #4412, #4427) and photometric (Margutti et al., ATel #4414; Martin et al., ATel #4416; Brimacombe, ATel #4423; Margutti et al., ATel #4425; Leonard et al. ATel #4430) changes from LBV-like behavior into an apparent SN explosion. We report low-resolution (R = 120, delta-V = 2500 km/s) 0.8-2.5 micron spectroscopy from IRTF/SpeX that confirms the interpretation of this event as a Type IIn SN. The source was observed on 2012 Sep 27.3 (8:00-8:30 UT) and found to be 1.8 mag brighter in a broad H+K notch filter than the close source located 5.4" to the NE. Bootstrapping from the Ks > 15.50 magnitude of that source from 2MASS suggests a magnitude of K ~ 13.7 for SN 2009ip. The spectral continuum is well-matched to a power law slope log10(f_lam) = -13.5576 -1.55246 * lam + 0.233246 lam^2, with f_lam in erg/cm2/s/Ang and lam in microns. Spectrophotometic colors are I-J = 0.16, J-H =0.22 and H-Ks = 0.26, and spectral flux scaling indicates Ks <~ 13.6 (not accounting for slit losses) The primary features in the spectrum are prominent and unresolved H I emission lines at 1.094 micron (Pa gamma, v width = 2100 km/s), 1.291 micron (Pa beta, v width = 1600 km/s) and 1.887 micron (Pa alpha, v width = 1100 km/s). The unresolved lines confirm the near-synchronous optical observations of Smith & Mauerhan, ATel, #4427, and supports the conclusion that this event has evolved into a Type IIn.