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An intermediate luminosity transient in NGC 300: The eruption of a dust-enshrouded massive star

Berger, E.; Soderberg, A.M.; Chevalier, R.A.; Fransson, C.; Foley, R.J.; Leonard, D.C.; Debes, J.H.; Diamond-Stanic, A.M.; Dupree, A.K. and Ivans, I.I., et al. (2009) In Astrophysical Journal 699(2). p.1850-1865
Abstract
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 NGC 300. We find that the transient (NGC 300 OT2008-1) has a peak absolute magnitude of M-bol approximate to -11.8 mag, intermediate between novae and supernovae, and similar to the recent events M85 OT2006-1 and SN 2008S. Our high-resolution spectra, the first for this event, are dominated by intermediate velocity (similar to 200-1000 km s(-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... (More)
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 NGC 300. We find that the transient (NGC 300 OT2008-1) has a peak absolute magnitude of M-bol approximate to -11.8 mag, intermediate between novae and supernovae, and similar to the recent events M85 OT2006-1 and SN 2008S. Our high-resolution spectra, the first for this event, are dominated by intermediate velocity (similar to 200-1000 km s(-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 similar to 10(3) km s(-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 x 10(4) L-circle dot, indicative of a similar to 10-20 M-circle dot 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. (Less)
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keywords
stars: evolution circumstellar matter stars: mass loss stars: winds, outflows
in
Astrophysical Journal
volume
699
issue
2
pages
1850 - 1865
publisher
University of Chicago Press
external identifiers
  • wos:000267401500084
  • scopus:68149171455
ISSN
0004-637X
DOI
10.1088/0004-637X/699/2/1850
language
English
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yes
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f33a6e34-fbef-47bc-aad7-8a3b7f98f8b4 (old id 1453794)
date added to LUP
2009-08-04 11:56:55
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@article{f33a6e34-fbef-47bc-aad7-8a3b7f98f8b4,
  abstract     = {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 NGC 300. We find that the transient (NGC 300 OT2008-1) has a peak absolute magnitude of M-bol approximate to -11.8 mag, intermediate between novae and supernovae, and similar to the recent events M85 OT2006-1 and SN 2008S. Our high-resolution spectra, the first for this event, are dominated by intermediate velocity (similar to 200-1000 km s(-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 similar to 10(3) km s(-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 x 10(4) L-circle dot, indicative of a similar to 10-20 M-circle dot 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.},
  author       = {Berger, E. and Soderberg, A.M. and Chevalier, R.A. and Fransson, C. and Foley, R.J. and Leonard, D.C. and Debes, J.H. and Diamond-Stanic, A.M. and Dupree, A.K. and Ivans, I.I. and Simmerer, Jennifer and Thompson, I.B. and Tremond, C.A.},
  issn         = {0004-637X},
  keyword      = {stars: evolution
circumstellar matter
stars: mass loss
stars: winds,outflows},
  language     = {eng},
  number       = {2},
  pages        = {1850--1865},
  publisher    = {University of Chicago Press},
  series       = {Astrophysical Journal},
  title        = {An intermediate luminosity transient in NGC 300: The eruption of a dust-enshrouded massive star},
  url          = {http://dx.doi.org/10.1088/0004-637X/699/2/1850},
  volume       = {699},
  year         = {2009},
}