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arXiv · 1912.00729

Short and long term near-infrared spectroscopic variability of eruptive protostars from VVV

Zhen Guo·P. W. Lucas·C. Contreras Peña·R. G. Kurtev·L. C. Smith·J. Borissova·J. Alonso-García·D. Minniti·A. Caratti o Garatti·D. Froebrich
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Abstract

Numerous eruptive variable young stellar objects (YSOs), mostly Class I systems, were recently detected by the near-infrared Vista Variables in the Via Lactea (VVV) survey. We present an exploratory near-infrared spectroscopic variability study of 14 eruptive YSOs. The variations were sampled over 1-day and 1 to 2-year intervals and analysed in combination with VVV light curves. CO overtone absorption features are observed on 3 objects with FUor-like spectra: all show deeper absorption when they are brighter. This implies stronger emission from the circumstellar disc with a steeper vertical temperature gradient when the accretion rate is higher. This confirms the nature of fast VVV FUor-like events, in line with the accepted picture for classical FUors. The absence of Br$γ$ emission in a FUor-like object declining to pre-outburst brightness suggests that reconstruction of the stellar magnetic field is a slow process. Within the 1-day timescale, 60% of H$_2$-emitting YSOs show significant but modest variation, and 2/6 sources have large variations in Br$γ$. Over year-long timescales, H$_2$ flux variations remain modest despite up to 1.8 mag variation in $K_s$. This indicates that emission from the molecular outflow usually arises further from the protostar and is unaffected by relatively large changes in accretion rate on year-long timescales. Two objects show signs of on/off magnetospheric accretion traced by Br$γ$ emission. In addition, a 60% inter-night brightening of the H$_2$ outflow is detected in one YSO.

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Zhen Guo, P. W. Lucas, C. Contreras Peña, R. G. Kurtev, L. C. Smith, J. Borissova, J. Alonso-García, D. Minniti, A. Caratti o Garatti, D. Froebrich. 2019-12-02. Short and long term near-infrared spectroscopic variability of eruptive protostars from VVV. https://doi.org/10.1093/mnras%2Fstz3374

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