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The Eruption of the Candidate Young Star ASASSN-15qi

Herczeg, GJ and Dong, S and Shappee, BJ and Chen, P and Hillenbrand, LA and Jose, J and Kochanek, CS and Prieto, JL and Stanek, KZ and Kaplan, K and Holoein, TW-S and Mairs, S and Johnstone, D and Gully-Santiago, M and Zhu, Z and Smith, MC and Bersier, D and Mulders, GD and Filippenko, AV and Ayani, K and Brimacombe, J and Brown, JS and Connelley, M and Harmanen, J and Ito, R and Kawabata, KS and Maehara, H and Takata, K and Yuk, H and Zheng, W (2016) The Eruption of the Candidate Young Star ASASSN-15qi. Astrophysical Journal, 831 (2). ISSN 0004-637X

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Abstract

Outbursts on young stars are usually interpreted as accretion bursts caused by instabilities in the disk or the star-disk connection. However, some protostellar outbursts may not fit into this framework. In this paper, we analyze optical and near-infrared spectra and photometry to characterize the 2015 outburst of the probable young star ASASSN-15qi. The $\sim 3.5$ mag brightening in the $V$ band was sudden, with an unresolved rise time of less than one day. The outburst decayed exponentially by 1 mag for 6 days and then gradually back to the pre-outburst level after 200 days. The outburst is dominated by emission from $\sim10,000$ K gas. An explosive release of energy accelerated matter from the star in all directions, seen in a spectacular cool, spherical wind with a maximum velocity of 1000 km/s. The wind and hot gas both disappeared as the outburst faded and the source the source returned to its quiescent F-star spectrum. Nebulosity near the star brightened with a delay of 10-20 days. Fluorescent excitation of H$_2$ is detected in emission from vibrational levels as high as $v=11$, also with a possible time delay in flux increase. The mid-infrared spectral energy distribution does not indicate the presence of warm dust emission, although the optical photospheric absorption and CO overtone emission could be related to a gaseous disk. Archival photometry reveals a prior outburst in 1976. Although we speculate about possible causes for this outburst, none of the explanations are compelling.

Item Type: Article
Uncontrolled Keywords: astro-ph.SR; astro-ph.SR
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: American Astronomical Society; IOP Publishing
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Date Deposited: 25 Nov 2016 12:09
Last Modified: 25 Nov 2016 12:09
DOI or Identification number: 10.3847/0004-637X/831/2/133
URI: http://researchonline.ljmu.ac.uk/id/eprint/3943

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