A SPITZER/IRS SPECTRUM OF THE 2008 LUMINOUS TRANSIENT IN NGC 300: CONNECTION TO PROTO-PLANETARY NEBULAE

Journal Article · Tue Nov 10 00:00:00 EST 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/705/2/1425· OSTI ID:21378279

Prieto, Jose L; Sellgren, Kris; Thompson, Todd A; Kochanek, Christopher S ^[1]

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1. Department of Astronomy, Ohio State University, 140 W. 18th Ave., Columbus, OH 43210 (United States)

We present a Spitzer/IRS low-resolution mid-infrared (mid-IR) spectrum (5-14 mum) of the luminous transient discovered in the nearby galaxy NGC 300 in 2008 May. This transient had peak luminosity M{sub V} approx = -13, showed an optical spectrum dominated by relatively narrow Balmer and Ca II lines in emission, and its progenitor was identified in pre-explosion images as a dust-enshrouded approx10 M {sub sun} star, characteristics that make it a twin of SN 2008S. The Spitzer spectrum, obtained three months after discovery, shows that the transient is very luminous in the mid-IR. Furthermore, the spectrum shows strong, broad emission features at 8 mum and 12 mum that are observed in Galactic carbon-rich proto-planetary nebulae. Combining these data with published optical and near-IR photometry obtained at the same epoch, we find that the mid-IR excess traced by the Spitzer spectrum accounts for approx20% of the total energy output. This component can be well explained by emission from approx3 x 10{sup -4} M{sub sun} of pre-existing progenitor dust at temperature T approx 400 K. The spectral energy distribution of the transient also shows a near-IR excess that can be explained by emission from newly formed dust in the ejecta. Alternatively, both the near-IR and mid-IR excesses can together be explained by a single pre-existing geometrically thick dust shell. In light of the new observations obtained with Spitzer, we revisit the analysis of the optical spectra and kinematics, which were compared to the massive yellow-hypergiant IRC+10420 in previous studies. We show that proto-planetary nebulae share many properties with the NGC 300 transient and SN 2008S. We conclude that even though the explosion of a massive star (M approx> 10 M{sub sun}) cannot be ruled out, an explosive event on a massive (M approx 6-10 M{sub sun}) carbon-rich AGB/super-AGB or post-AGB star is consistent with all observations of the transients and their progenitors presented thus far.

• OSTI ID: 21378279
• Journal Information: Astrophysical Journal, Vol. 705, Issue 2; Other Information: DOI: 10.1088/0004-637X/705/2/1425; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
CARBON
DUSTS
EMISSION
ENERGY SPECTRA
EXPLOSIONS
GALAXIES
INFRARED SPECTRA
LUMINOSITY
PHOTOMETRY
PLANETARY NEBULAE
STAR EVOLUTION
SUPERNOVAE
BINARY STARS
ELEMENTS
ERUPTIVE VARIABLE STARS
EVOLUTION
NEBULAE
NONMETALS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
SPECTRA
STARS
VARIABLE STARS