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Published November 10, 2016 | Published + Submitted
Journal Article Open

The Eruption of the Candidate Young Star ASASSN-15QI


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 ~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 ~10,000 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^(−1). The wind and hot gas both disappeared as the outburst faded and the source returned to its quiescent F-star spectrum. Nebulosity near the star brightened with a delay of 10–20 days. Fluorescent excitation of H2 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, though 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.

Additional Information

© 2016 The American Astronomical Society. Received 2016 May 10; revised 2016 June 30; accepted 2016 July 19; published 2016 November 3. We thank the anonymous referee for useful comments and a prompt report. G.J.H. thanks John Kwan, Bob Williams, Fred Walter, Dong Lai, Doug Lin, and Bo Reipurth for interesting conversations about ASASSN-15qi. We thank LCOGT and its staff for their continued support of ASAS-SN. G.J.H. is supported by general grant 11473005 awarded by the National Science Foundation of China. S.D. and P.C. are supported by "the Strategic Priority Research Program—The Emergence of Cosmological Structures" of the Chinese Academy of Sciences (Grant No. XDB09000000) and Project 11573003 supported by NSFC. This research uses data obtained through the Telescope Access Program (TAP), which is also funded by Grant No. XDB09000000 from the Chinese Academy of Sciences and by the Special Fund for Astronomy from the Ministry of Finance. B.S. is supported by NASA through Hubble Fellowship grant HF-51348.001 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. CSK and KZS are supported by NSF grants AST-1515876 and AST-1515927. TW-SH is supported by the DOE Computational Science Graduate Fellowship, grant number DE-FG02-97ER25308. Support for J.L.P. is in part provided by FONDECYT through grant 1151445 and by the Ministry of Economy, Development, and Tourism's Millennium Science Initiative through grant IC120009, awarded to The Millennium Institute of Astrophysics, MAS. Development of ASAS-SN has been supported by NSF grant AST-0908816 and CCAPP at the Ohio State University. ASAS-SN is supported by NSF grant AST-1515927, the Center for Cosmology and AstroParticle Physics (CCAPP) at OSU, the Mt. Cuba Astronomical Foundation, George Skestos, and the Robert Martin Ayers Sciences Fund. AVF's group at UC Berkeley is grateful for financial assistance from NSF grant AST-1211916, the TABASGO Foundation, Clark and Sharon Winslow, and the Christopher R. Redlich Fund. Research at Lick Observatory is partially supported by a generous gift from Google. This research was made possible through the use of the AAVSO Photometric All-Sky Survey (APASS) funded by the Robert Martin Ayers Sciences Fund, data provided by Astrometry.net (Lang et al. 2010), and filter curves from the Visual Observatory. The Liverpool Telescope is operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias with financial support from the UK Science and Technology Facilities Council. We thank the Swift ToO team for responding quickly to our observation requests. Some data presented here were made with the Nordic Optical Telescope, operated by the Nordic Optical Telescope Scientific Association at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofisica de Canarias. Some data presented here were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. Some ESPaDOnS data were downloaded from the CFHT archive, which is supported by the Canadian Astronomy Data Centre. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. This work used the Immersion Grating Infrared Spectrograph (IGRINS) that was developed under a collaboration between the University of Texas at Austin and the Korea Astronomy and Space Science Institute (KASI) with the financial support of the US National Science Foundation under grant AST-1229522, of the University of Texas at Austin, and of the Korean GMT Project of KASI. The James Clerk Maxwell Telescope is operated by the East Asian Observatory on behalf of The National Astronomical Observatory of Japan, Academia Sinica Institute of Astronomy and Astrophysics, the Korea Astronomy and Space Science Institute, the National Astronomical Observatories of China and the Chinese Academy of Sciences (Grant No. XDB09000000), with additional funding support from the Science and Technology Facilities Council of the United Kingdom and participating universities in the United Kingdom and Canada. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

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Published - Herczeg_2016_ApJ_831_133.pdf

Submitted - 1607.06368v3.pdf


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