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The past several years have seen the discovery of a new class of
astrophysical transients. They have maximum luminosities intermediate
between classical novae and supernovae, and typically become extremely
red as their outbursts proceed over several months. I call them
Intermediate-Luminosity Red Transients (ILRTs).
In the Milky Way, the ILRTs include V838 Monocerotis (which illuminated
a spectacular light echo) and the recent V1309 Scorpii. Possibly related
extragalactic ILRTs include the Andromeda red variable of 1988 (M31 RV),
the 2006 transient in M85, SN 2008S, and the 2008 and 2010 events in the
nearby southern-hemisphere galaxy NGC 300.
I will present remarkable HST images of the V838 Mon light echo, and
explain how polarimetric imaging of the echo led to a geometric
distance. Recent X-ray and optical observations suggest that the
outbursts of V838 Mon and V1309 Sco were due to violent stellar mergers.
However, several of the extragalactic ILRT outbursts appear to have
arisen from deeply dust-enshrouded massive stars and may have an origin
related to Luminous Blue Variables. I will review the possible range of
scenarios that may explain these intriguing new objects.
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