Accretion, jets and winds: High-energy emission from young stellar objects
Abstract
This article summarizes the processes of high-energy emission in young stellar objects. Stars of spectral type A and B are called Herbig Ae/Be (HAeBe) stars in this stage, all later spectral types are termed classical T Tauri stars (CTTS). Both types are studied by high-resolution X-ray and UV spectroscopy and modeling. Three mechanisms contribute to the high-energy emission from CTTS: 1) CTTS have active coronae similar to main-sequence stars, 2) the accreted material passes through an accretion shock at the stellar surface, which heats it to a few MK, and 3) some CTTS drive powerful outflows. Shocks within these jets can heat the plasma to X-ray emitting temperatures. Coronae are already well characterized in the literature; for the latter two scenarios models are shown. The magnetic field suppresses motion perpendicular to the field lines in the accretion shock, thus justifying a 1D geometry. The radiative loss is calculated as optically thin emission. A mixture of shocked and coronal gas is fitted to X-ray observations of accreting CTTS. Specifically, the model explains the peculiar line-ratios in the He-like triplets of Ne IX and O VII. All stars require only small mass accretion rates to power the X-ray emission. In contrast, the HAeBe HD 163296 has line ratios similar to coronal sources, indicating that neither a high density nor a strong UV-field is present in the region of the X-ray emission. This could be caused by a shock in its jet. Similar emission is found in the deeply absorbed CTTS DG Tau. Shock velocities between 400 and 500 km s-1 are required to explain the observed spectrum.
Doctoral Thesis Award Lecture 2010- Publication:
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Astronomische Nachrichten
- Pub Date:
- June 2011
- DOI:
- 10.1002/asna.201111559
- arXiv:
- arXiv:1106.2840
- Bibcode:
- 2011AN....332..448G
- Keywords:
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- accretion;
- accretion disks;
- circumstellar matter;
- ISM: jets and outflows;
- stars: winds;
- outflows;
- T Tauri stars;
- X-rays: stars;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- Astronomische Nachrichten, Vol.332, Issue 5, p.448, 2011