The outflowing wind of V1057 cygni

Abstract

In 1970-1971, V1057 Cyg rose from about m pg 16 to a peak near 10.5 mag. It has subsequently faded to about B = 15, and although it appeared to be a T Tauri star (TTS) before the outburst, it now resembles a rather peculiar rapidly rotating G-type supergiant. Before the outburst, it showed unmistakable evidence of high-velocity outflow (by the suppression of emission Ca II λ3968 by the P Cyg absorption component of Hε λ3970). Such outflow absorptions are currently found at many strong lines (Hα, Na I D1,2, K I λλ7664, 7698, Ca II λλ8498, 8662, ...). The same phenomenon has since been observed in a number of other FUors near maximum light, suggesting that it is a FUor characteristic that clearly differs from the outflows found in TTSs. The Li I resonance line at 6707 is relatively weak, and on high-resolution spectra obtained between 1997 and 2008 showed variable absorption structure on its shortward side that probably represents wind structure that is lost in the stronger lines. In addition, a narrow emission line at 6707 persists throughout the series and is the counterpart of the sharp emission lines that occur near the centers of many of the broad stellar absorption lines (v sin i = 55 km s-1) and that were responsible for the line-splitting phenomenon formerly regarded as evidence of a Keplerian disk. Given the evidence of a quasi-permanent outflow at V1057 Cyg, the hypothesis is advanced that a FUor outburst may be the result of a rapidly rotating TTS having contracted to a point of rotational instability, at which time it sheds enough material and angular momentum to resume contraction, until the next such event. © 2009. The American Astronomical Society. All rights reserved.