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Massive star mergers and the recent transient in NGC 4490: A more massive cousin of V838 Mon and V1309 Sco

Smith, N and Andrews, JE and Van Dyk, SD and Mauerhan, JC and Kasliwal, MM and Bond, HE and Filippenko, AV and Clubb, KI and Graham, ML and Perley, DA and Jencson, J and Bally, J and Ubeda, L and Sabbi, E (2016) Massive star mergers and the recent transient in NGC 4490: A more massive cousin of V838 Mon and V1309 Sco. Monthly Notices of the Royal Astronomical Society, 458 (1). pp. 950-962. ISSN 0035-8711

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Abstract

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 a recent optical and infrared (IR) transient discovered in the nearby galaxy NGC4490 named NGC4490-OT2011 (NGC 4490-OT hereafter), which appeared similar to these merger events (unobscured progenitor, irregular multi-peaked light curve, increasingly red colour, 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 Hubble Space Telescope (HST) images, combined with upper limits in the IR, requires a luminous and blue progenitor that has faded in late-time HST images. The same source was detected by Spitzer and groundbased data as a luminous IR (2-5 μm) transient, indicating a transition to a self-obscured state qualitatively similar to the evolution seen in other stellar mergers and in luminous blue variables. The post-outburst dust-obscured source is too luminous and too warm at late times to be explained with an IR echo, suggesting that the object survived the event. The luminosity of the enshrouded IR source is similar to that of the progenitor. Compared to proposed merger events, the more massive progenitor of NGC4490-OT seems to extend a correlation between stellar mass and peak luminosity, and may suggest that both of these correlate with duration. We show that spectra of NGC4490-OT and V838 Mon also resemble light-echo spectra of η Car, prompting us to speculate that η Car may be an extreme extension of this phenomenon.

Item Type: Article
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2016 The Auhtors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords: 0201 Astronomical And Space Sciences
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press
Date Deposited: 17 Feb 2017 12:31
Last Modified: 17 Feb 2017 12:31
DOI or Identification number: 10.1093/mnras/stw219
URI: http://researchonline.ljmu.ac.uk/id/eprint/5609

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