Massive-Star Mergers and the Recent Transient in NGC4490: A More Massive Cousin of V838 Mon and V1309 Sco

Understand

The Galactic transient V1309 Sco was the result of a merger in a low-mass star system, while V838 Mon was thought to be a similar merger event from a more massive B-type progenitor.

• In this paper we study an optical/IR transient discovered in the nearby galaxy NGC4490, which appeared similar to these merger events (unobscured progenitor, irregular multi-peaked light curve, increasingly red color, similar optical spectrum, IR excess at late times), but which had a higher peak luminosity and longer duration in outburst.
• NGC4490-OT has less in common with the class of SN~2008S-like transients.
• A progenitor detected in pre-eruption HST images, combined with upper limits in the IR, requires a luminous and blue progenitor that has faded in late-time HST images.