LIGHT ECHOES FROM η CARINAE'S GREAT ERUPTION: SPECTROPHOTOMETRIC EVOLUTION AND THE RAPID FORMATION OF NITROGEN-RICH MOLECULES
- Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ 08544 (United States)
- Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
- Department of Physics, New York University, New York, NY 10012 (United States)
- National Optical Astronomy Observatory, Tucson, AZ 85719 (United States)
- Steward Observatory, University of Arizona, Tucson, Arizona 85721 (United States)
- Las Campanas Observatory, Carnegie Observatories, Casilla 601, La Serena (Chile)
- Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
- Cerro Tololo Inter-American Observatory, Casilla 603, La Serena (Chile)
- Leibniz-Institut für Astrophysik Potsdam, an der Sternwarte 16, D-14482, Potsdam (Germany)
- Gemini Observatory, Southern Operations Center, Casilla 603, La Serena (Chile)
- Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1 (Canada)
We present follow-up optical imaging and spectroscopy of one of the light echoes of η Carinae's nineteenth century Great Eruption discovered by Rest et al. By obtaining images and spectra at the same light echo position between 2011 and 2014, we follow the evolution of the Great Eruption on a 3 yr timescale. We find remarkable changes in the photometric and spectroscopic evolution of the echo light. The i-band light curve shows a decline of ∼0.9 mag in ∼1 yr after the peak observed in early 2011 and a flattening at later times. The spectra show a pure-absorption early G-type stellar spectrum at peak, but a few months after peak the lines of the Ca II triplet develop strong P-Cygni profiles and we see the appearance of [Ca II] 7291, 7324 doublet in emission. These emission features and their evolution in time resemble those observed in the spectra of some Type IIn supernovae and supernova impostors. Most surprisingly, starting ∼300 days after peak brightness, the spectra show strong molecular transitions of CN at ≳ 6800 Å. The appearance of these CN features can be explained if the ejecta are strongly nitrogen enhanced, as is observed in modern spectroscopic studies of the bipolar Homunculus nebula. Given the spectroscopic evolution of the light echo, velocities of the main features, and detection of strong CN, we are likely seeing ejecta that contributes directly to the Homunculus nebula.
- OSTI ID:
- 22365841
- Journal Information:
- Astrophysical Journal Letters, Vol. 787, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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