Infall variability in the Classical T Tauri system VZ Chamaeleonis

Abstract

Abstract. We present time series spectroscopy of the Classical T Tauri star VZ Cha. We follow spectral variations at intermediate resolution over five successive nights, or approximately two rotation periods. We see profile features which persist on timescales longer than the expected infall time from the inner disc, and we see expected evidence of rotational variations in the lines, but we also note that rotation alone cannot produce all the observed variability and some other mechanism must be invoked. The behaviour of Hα is observed to be markedly different from that of the other lines. In particular, the evidence of rotational effects is lacking at Hα, and the activity in the red and blue wings of the line is not significantly correlated, in contrast to the other Balmer lines.

Emission-line profile modelling of structured T Tauri magnetospheres

“…Only the D150 model, which has wide accretion curtains, shows a variability that is comparable to published data e.g. Smith et al (2001). The geometry with the least symmetry (A30) leads to line profiles that change substantially in shape and intensity from one rotation phase to another.…”

“…It was suggested that the accretion flow had an azimuthal component and that the observer's line of sight was sampling different physical environments for line formation. Structured accretion is also supported by the observations of VZ Cha (Smith et al 2001) who report features that persist for longer than the likely free‐fall time from the inner edge of a truncated disc. The possibility of confinement to two rotating streams was considered, with the observed period being only half the stellar rotation period.…”

“…The accretion flows are confined to two azimuthal curtains around the star so that their projection against the stellar disc and hotspots changes during a rotation cycle. This scenario was suggested by Smith et al (2001) as an explanation for the periodicity in the spectra of VZ Cha.…”

“…While observations of comparable spectra can compensate for these effects (e.g. Edwards et al 1994), these corrections introduce their own uncertainties and many authors present spectra without such processing (Alencar et al 2001; Smith et al 2001).…”

“…The observer is probably seeing a geometry with overall characteristics persisting for longer than the rotational time‐scale, but with some structure varying more rapidly. The accretion rate is also expected to show changes on short time‐scales dependent on the changing magnetic field configuration (Smith et al 2001).…”