"Reading between the lines": Using time- and velocity-resolved data to map accretion structures around stars

Accretion is one of the defining characteristics of young stars. For the late-type ones, accretion is channelled by the stellar magnetic field. Magnetospheric accretion thus connects the protoplanetary disk to the young star and opens a gap in the innermost disk, which can affect planet migration. While direct mapping cannot access these regions, emission (and absorption) lines in young stars trace their winds, accretion-related structures, spots, and sometimes, the innermost disk.

Young stars are rich in emission (and absorption) lines, related to their winds, accretion, hot spots, and innermost gaseous disk. Optical, near-UV, and near-IR lines include a large number of species with various excitation potentials that can provide information on the temperature, density, and velocity of hot and tiny structures. Combining the velocity information with repeated, time-resolved data, we can reconstruct scales of a few stellar radii. With time-resolved spectroscopy covering several rotational and disk orbital periods, we can obtain a detailed view of the structure and variability of accretion columns and spots and information on the presence and launching points of stellar/disk winds in young stars. Data acquired over months-to-year can reveal the long-term stability of the accretion process and related structures.

Understanding these processes and how they affect the observed spectra can also help us to identify (or rule out) the presence of young and newly-formed planets and stellar companions that may be perturbing the disk. Highly variable and outbursting sources provide a further point: with the temperature varying during outbursts, we can spectroscopically access an even larger region of the stellar surroundings and even the disk.

In this poster we present the results for stars with different spectral types and behaviours, and show the application of the STAR-MELT code we created in Dundee for this type of analysis (see also poster by J. Campbell-White), exploring what we can learn from "reading between their (spectral) lines". We explore the location of the accretion post-shock regions and accretion column footprints and unveil stable (often, for years) and unstable accretion in different types of stars and the presence of infall and non-axisymmetric winds. We further discuss how this can help us to unveil why wild and variable stars are so wild.