An intermediate luminosity transient in NGC300: The eruption of a dust-enshrouded massive star

E. Berger, A. M. Soderberg, R. A. Chevalier, C. Fransson, R. J. Foley, D. C. Leonard, J. H. Debes, A. M. Diamond-Stanic, A. K. Dupree, I. I. Ivans, J. Simmerer, I. B. Thompson, C. A. Tremonti

Research output: Contribution to journalArticlepeer-review


We present multi-epoch high-resolution optical spectroscopy, UV/radio/X-ray imaging, and archival Hubble and Spitzer observations of an intermediate luminosity optical transient recently discovered in the nearby galaxy NGC300. We find that the transient (NGC300OT2008-1) has a peak absolute magnitude of M bol -11.8 mag, intermediate between novae and supernovae, and similar to the recent events M85OT2006-1 and SN2008S. Our high-resolution spectra, the first for this event, are dominated by intermediate velocity (200-1000kms -1) hydrogen Balmer lines and Ca II emission and absorption lines that point to a complex circumstellar environment, reminiscent of the yellow hypergiant IRC+10420. In particular, we detect asymmetric Ca II H&K absorption with a broad red wing extending to 103kms-1, indicative of gas inflow at high velocity (possibly the wind of a massive binary companion). The low luminosity, intermediate velocities, and overall similarity to a known eruptive star indicate that the event did not result in a complete disruption of the progenitor. We identify the progenitor in archival Spitzer observations, with deep upper limits from Hubble data. The spectral energy distribution points to a dust-enshrouded star with a luminosity of about 6 × 104 L 1, indicative of a 10-20 M 1 progenitor (or binary system). This conclusion is in good agreement with our interpretation of the outburst and circumstellar properties. The lack of significant extinction in the transient spectrum indicates that the dust surrounding the progenitor was cleared by the outburst. We thus predict that the progenitor should be eventually visible with Hubble if the transient event marks an evolutionary transition to a dust-free state, or with Spitzer if the event marks a cyclical process of dust formation.

Original languageEnglish (US)
Pages (from-to)1850-1865
Number of pages16
JournalAstrophysical Journal
Issue number2
StatePublished - 2009
Externally publishedYes


  • Circumstellar matter
  • Stars: evolution
  • Stars: mass loss
  • Stars: winds, outflows

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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