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Published February 10, 2017 | Submitted + Published
Journal Article Open

A Continuum of Accretion Burst Behavior in Young Stars Observed by K2


We present 29 likely members of the young ρ Oph or Upper Sco regions of recent star formation that exhibit "accretion burst" type light curves in K2 time series photometry. The bursters were identified by visual examination of their ~80-day light curves, though all satisfy the M < -0.25 flux asymmetry criterion for burst behavior defined by Cody et al. The burst sources represent ≈9% of cluster members with strong infrared excess indicative of circumstellar material. Higher amplitude burster behavior is correlated with larger inner disk infrared excesses, as inferred from WISE W1 – W2 color. The burst sources are also outliers in their large Hα emission equivalent widths. No distinction between bursters and non-bursters is seen in stellar properties such as multiplicity or spectral type. The frequency of bursters is similar between the younger, more compact ρ Oph region, and the older, more dispersed Upper Sco region. The bursts exhibit a range of shapes, amplitudes (~10%–700%), durations (~1–10 days), repeat timescales (~3–80 days), and duty cycles (~10%–100%). Our results provide important input to models of magnetospheric accretion, in particular, by elucidating the properties of accretion-related variability in the low state between major longer duration events such as EX Lup and FU Ori type accretion outbursts. We demonstrate the broad continuum of accretion burst behavior in young stars—extending the phenomenon to lower amplitudes and shorter timescales than traditionally considered in the theory of pre-main sequence accretion history.

Additional Information

© 2017 The American Astronomical Society. Received 2016 September 2; revised 2016 December 15; accepted 2016 December 20; published 2017 February 7. The work of AMC was supported by a NASA/NPP fellowship. We thank the referee for useful feedback that improved this paper. We acknowledge Luisa Rebull for calling our attention to one of the burst type objects that we had overlooked in our initial examination. Thanks also to Nic Scott for assistance with DSSI observations on the Gemini South telescope. This paper includes data collected by the K2 mission. Funding for the K2 mission is provided by the NASA Science Mission directorate. The spectroscopic data 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. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. These results are also based on observations obtained as part of the program GS-2016A-Q-64 at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), and Ministério da Ciência, Tecnologia e Inovação (Brazil). This paper has utilized the SIMBAD and Vizier services, through which data from USNO-B, APASS, 2MASS, and WISE were collected.

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Published - Cody_2017_ApJ_836_41.pdf

Submitted - 1612.05599.pdf


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