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SN 2009ip: Follow-up optical and NIR spectroscopy

ATel #4435; J. Vinkó (U of Szeged), J. C. Wheeler (U of Texas at Austin), D. Milisavljevic, G. H. Marion, A. M. Soderberg (CfA, Harvard), R. Fesen, N. Utterback (Dartmouth College), P. Roming, T. Pritchard (PSU)
on 28 Sep 2012; 16:59 UT
Credential Certification: Jozsef Vinko (vinko@astro.as.utexas.edu)

Subjects: Infra-Red, Optical, Supernovae

Referred to by ATel #: 4439, 4454, 4477, 4479, 4491

We obtained two optical spectra (wavelength range 3500 - 9000 A, resolution FWHM ~18 A) with the Robert Stobie Spectrograph (RSS) mounted on the Southern African Large Telescope (SALT), of SN 2009ip following its recent outburst (Drake et al., ATel #4334). The first spectrum was taken on Aug 26, 2012, almost contemporaneous with the one reported by Foley et al. (ATel #4338). Our spectrum showed prominent H emission features at their rest wavelengths, having ~600 km/s FWHM, similar to the value given by Foley et al. In addition, much broader P Cygni features were also clearly identifiable for H-alpha, H-beta and H-gamma. The velocities estimated from the absorption minima of these P Cygni features were ~10,000 km/s for all of them. A similar P Cygni feature was detected at the expected wavelength of the He I 5876 line, although without the narrow emission component, unlike for the H features. These P Cygni lines appeared similar to those broad features that were present in the spectra obtained on Sept 15-16 by Smith & Mauerhan (ATel #4412). Thus, we confirm the report by Smith & Mauerhan that before the most recent re-brightening started around Sept 24 (Brimacombe, ATel #4423; Margutti et al., ATel #4425; Leonard et al., ATel #4430), the spectrum of SN 2009ip contained broad P Cygni-like features of H and He I, typical for Type II SNe. The second, high S/N optical spectrum taken with SALT/RSS with the same setup on Sept 26, 2012 shows that the narrow emission components have strengthened, while the P Cygni components are considerably supressed, similar to the recent report by Smith & Mauerhan (ATel #4427). The slope of the continuum has also become somewhat bluer relative to that of the Aug 26 spectrum. The P Cygni components for the H Balmer features are still weakly present, but the velocities from their absorption minima are reduced to ~5000 km/s. This is also true for the He I 5876 feature, but the narrow emission component, which was absent in the Aug 26 spectrum, now became prominent. We also clearly detect the emission features of He I 5016, 6678 and 7065 at their rest wavelength. A plot of the optical spectra can be accessed at the following URL: http://www.as.utexas.edu/~vinko/sn09ip_salt.jpg In addition, low-resolution NIR spectra (range 0.9 - 2.4 micron; R = 750) were obtained Sept 27.2 UT at MDM Observatory with the 2.4m Hiltner telescope (+ TIFKAM). Preliminary reduction of these data reveal that emission features having FWHM ~2000 km/s are observed around the hydrogen Paschen lines. These spectra are consistent with NIR spectra reported by Burgasser et al. (ATel #4431), and support the conclusions of Smith & Mauerhan (ATel #4427) made from contemporaneous optical spectra that SN 2009ip is showing early phases of a luminous Type IIn supernova. Further follow-up observations are ongoing.