2010CBET.2292....3C

R. Chornock and E. Berger, Harvard University, report on imaging and spectroscopy of 2010da, obtained on May 25.4 UT with GMOS on the Gemini-South telescope. The spectra (range 350-1000 nm) exhibit strong, narrow emission lines of the H Balmer and Paschen series. The FWHM of H-alpha is approximately 660 km/s, although the line profile is not well-fitted by a Gaussian. The higher-order Balmer lines exhibit blueshifted P-Cyg absorption components. Emission lines of He I, Fe II, Ca II H and K, and O I are present, as is He II 468.6-nm. No strong absorption lines from Na I D are seen, indicative of low reddening, and consistent with the Swift detections in the ultraviolet (http://www.astronomerstelegram.org/?read=2633). In addition, although [Ca II] 729.1-nm falls in a CCD chip gap, [Ca II] 732.4-nm does not appear to be present in these GMOS spectra. The Gemini-South acquisition images yield a magnitude of r = 16.2. These spectral properties, combined with the low luminosity relative to supernovae (http://www.astronomerstelegram.org/?read=2632 http://www.astronomerstelegram.org/?read=2633), are indicative of a luminous- blue-variable-like outburst of a massive star.