# The Eruption of the Candidate Young Star ASASSN-15qi

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

## 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 astro-ph.SR; astro-ph.SR Q Science > QB AstronomyQ Science > QC Physics Astrophysics Research Institute American Astronomical Society; IOP Publishing Author 25 Nov 2016 12:09 17 Sep 2018 05:36 10.3847/0004-637X/831/2/133 http://researchonline.ljmu.ac.uk/id/eprint/3943