TY - JOUR
T1 - An intermediate luminosity transient in NGC300
T2 - The eruption of a dust-enshrouded massive star
AU - Berger, E.
AU - Soderberg, A. M.
AU - Chevalier, R. A.
AU - Fransson, C.
AU - Foley, R. J.
AU - Leonard, D. C.
AU - Debes, J. H.
AU - Diamond-Stanic, A. M.
AU - Dupree, A. K.
AU - Ivans, I. I.
AU - Simmerer, J.
AU - Thompson, I. B.
AU - Tremonti, C. A.
PY - 2009
Y1 - 2009
N2 - 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.
AB - 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.
KW - Circumstellar matter
KW - Stars: evolution
KW - Stars: mass loss
KW - Stars: winds, outflows
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U2 - 10.1088/0004-637X/699/2/1850
DO - 10.1088/0004-637X/699/2/1850
M3 - Article
AN - SCOPUS:68149171455
SN - 0004-637X
VL - 699
SP - 1850
EP - 1865
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
ER -