Time variability of accretion, outflows and star–disk interaction in Young Stellar Objects
Final Report Abstract
In the framework of this funding proposal the main topic was, as planned, a detailed spectroscopic monitoring study of the young, very low-mass star Par-Lup3-4. Besides this another work, initiated by the position holder before the start of his contract at Universität Tübingen, on the identification of young stars was completed. The photometric monitoring of TWA 30A and B was postponed. Par-Lup3-4 displays a rich emission-line spectrum, hosts a disc with an almost edge-on inclination, and is in the critical mass range near the star-brown dwarf transition, where the knowledge of the accretion-outflow connection remains rather poor. These properties make this star a prime target for conducting a variability study of mass accretion. The unique capabilities of X-shooter were used to monitor its broad-band spectrum in the range from the ultraviolet to the near-infrared. From the ten spectra of Par-Lup3-4 we studied its accretion diagnostics from emission lines and continuum excess due to accretion shocks, and derived its stellar parameters. This follow-up made it possible to investigate the accretion variability of time scales in hours, days, weeks, and years. Most emission line profiles show significant variations, but they result only in a small variation of the accretion luminosity and no noticeable change in extinction (AV ∼ 2 mag). This is in contrast to previous findings that suggested either no (AV = 0 mag) or a grey, that is wavelength-independent, extinction for Par-Lup3-4. The value of the extinction has a strong impact on the derived mass accretion rate, which differs by at least a factor of five for the different extinction estimates. The one spectrum acquired in 2012 remains quite puzzling: deviating behavior of Balmer versus Calcium fluxes, overluminous forbidden emission lines and poorly constrained extinction measurement. All these peculiarities are likely to be attributed to a contrast effect that stems from the singular alignment of the slit with the disc during this observing epoch, while the other spectra were taken at arbitrary (mis-)alignments with the disk due to the fact that X-Shooter’s capability of defining the slit orientation was not available during the observing period. This instrumental limitation impinges on the interpretation of variability seen between the different epochs as intrinsic and geometric effects are superposed on each other.
Publications
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Variability study of accretion and outflows in the very low-mass star Par-Lup3-4, Contributed talk in Special Session 16 at European Week of Astronomy & Space Science (EWASS) 2019, 24-28 June, Lyon, France;
Klutsch A., Stelzer B. & Alcalá J.M.
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Variability of the mass accretion rate in the very low-mass star Par-Lup3-4, Poster presented at The 20.5th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun (CS20.5), March 2-4, 2021
Klutsch A., Stelzer B. & Alcalá J.M.
