Reading between the lines

Abstract

Aims. We use optical spectroscopy to investigate the disk, wind, and accretion during the 2008 Z CMa NW outburst. Methods. Emission lines were used to constrain the locations, densities, and temperatures of the structures around the star. Results. More than 1000 optical emission lines reveal accretion, a variable, multicomponent wind, and double-peaked lines of disk origin. The variable, non-axisymmetric, accretion-powered wind has slow (~0 km s−1), intermediate (approximately −100 km s−1), and fast (≥−400 km s−1) components. The fast components are of stellar origin and disappear in quiescence, while the slow component is less variable and could be related to a disk wind. The changes in the optical depth of the lines between outburst and quiescence reveal that increased accretion is responsible for the observed outburst. We derive an accretion rate of 10−4 M⊙ yr−1 in outburst. The Fe I and weak Fe II lines arise from an irradiated, flared disk at ~0.5–3 × M*/16 M⊙ au with asymmetric upper layers, revealing that the energy from the accretion burst is deposited at scales below 0.5 au. Some line profiles have redshifted asymmetries, but the system is unlikely to be sustained by magnetospheric accretion, especially in outburst. The accretion-related structures extend over several stellar radii and, like the wind, are likely to be non-axisymmetric. The stellar mass may be ~6–8 M⊙, lower than previously thought (~16 M⊙). Conclusions. Emission line analysis is found to be a powerful tool to study the innermost regions and accretion in stars within a very large range of effective temperatures. The density ranges in the disk and accretion structures are higher than in late-type stars, but the overall behavior, including the innermost disk emission and variable wind, is very similar for stars with different spectral types. Our work suggests a common outburst behavior for stars with spectral types ranging from M type to intermediate mass.

Measuring Optical Extinction Towards Young Stellar Objects Using Diffuse Interstellar Bands

“…This included several objects studied and published as YSO outbursts by the second author, as well as noting the presence of DIBs in YSO spectra published by others, e.g. Sicilia-Aguilar et al (2020). Motivated by these findings, we initiated a more systematic investigation into the presence of DIBs features in young stars.…”

A Study of the Photometric and Spectroscopic Variations of the Prototypical FU Orionis–type Star V1057 Cyg

“…2). Since both depth and velocity change over time discontinuously, this variation over time can be interpreted as a rapidly-changing wind or rotation of non-axisymmetric components (Powell et al 2012;Sicilia-Aguilar et al 2020).…”

Protostellar outflows: a window to the past

“…If the accretion and ejection of gas are strongly coupled, episodic accretion events can be indirectly detected by the episodic outflows they trigger (Arce et al 2007 ;Vorobyov et al 2018 ;Sicilia-Aguilar et al 2020 ). In particular, where the rapidly ejected high-velocity gas shocks against the slower gas inside the cavity, it produces high-velocity outflow bullets, a frequently observed characteristic of protostellar outflows (Chen et al 2016 ;Cheng et al 2019 ;Tychoniec et al 2019 ).…”