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Impacts of fragmented accretion streams onto Classical T Tauri Stars: UV and X-ray emission lines | | Salvatore Colombo
; Salvatore Orlando
; Giovanni Peres
; Costanza Argiroffi
; Fabio Reale
; | | Date: |
11 Jul 2016 | | Abstract: | Context. The accretion process in Classical T Tauri Stars (CTTSs) can be
studied through the analysis of some UV and X-ray emission lines which trace
hot gas flows and act as diagnostics of the post-shock downfalling plasma. In
the UV band, where higher spectral resolution is available, these lines are
characterized by rather complex profiles whose origin is still not clear.
Aims. We investigate the origin of UV and X-ray emission at impact regions of
density structured (fragmented) accretion streams.We study if and how the
stream fragmentation and the resulting structure of the post-shock region
determine the observed profiles of UV and X-ray emission lines.
Methods. We model the impact of an accretion stream consisting of a series of
dense blobs onto the chromosphere of a CTTS through 2D MHD simulations. We
explore different levels of stream fragmentation and accretion rates. From the
model results, we synthesize C IV (1550 {AA}) and OVIII (18.97 {AA}) line
profiles.
Results. The impacts of accreting blobs onto the stellar chromosphere produce
reverse shocks propagating through the blobs and shocked upflows. These
upflows, in turn, hit and shock the subsequent downfalling fragments. As a
result, several plasma components di?ering for the downfalling velocity,
density, and temperature are present altoghether. The profiles of C IV doublet
are characterized by two main components: one narrow and redshifted to speed
$approx$ 50 km s$^{-1}$ and the other broader and consisting of subcomponents
with redshift to speed in the range 200 $approx$ 400 km s$^{-1}$. The profiles
of OVIII lines appear more symmetric than C IV and are redshifted to speed
$approx$ 150 km s$^{-1}$.
Conclusions. Our model predicts profiles of C IV line remarkably similar to
those observed and explains their origin in a natural way as due to stream
fragmentation. | | Source: | arXiv, 1607.3009 | | Services: | Forum | Review | PDF | Favorites | |
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