Issue |
A&A
Volume 369, Number 3, April III 2001
|
|
---|---|---|
Page(s) | 993 - 1008 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20010203 | |
Published online | 15 April 2001 |
Non-axisymmetric accretion on the classical TTS RW Aur A*
1
Astronomy Division, PO Box 3000, 90014 University of Oulu, Finland
2
Stockholm Observatory, 133 36 Saltsjöbaden, Sweden
3
CAUP, Universidade do Porto, Rua das Estrelas, 4150 Porto, Portugal
4
Departamento de Matemática Aplicada, Rua das Taipas, 135, 4150 Porto, Portugal
Corresponding author: P. P. Petrov, Peter.Petrov@Oulu.Fi
Received:
7
September
2000
Accepted:
1
February
2001
High-resolution spectroscopic monitoring of the exceptionally
active classical T Tauri star (CTTS) RW Aur A was carried out in
three seasons of 1996, 1998 and 1999 with simultaneous B, V
photometry. The high quality spectra revealed a multicomponent
structure of the spectrum, which includes: 1) a veiled photospheric
spectrum of a K1-K4 star, 2) broad emission lines of neutrals and
ions, 3) narrow emission lines of Hei
and Heii, 4) red-shifted
accretion features of many lines, 5) shell lines at about the
stellar velocity, 6) blue-shifted wind features and 7) forbidden
lines.
Periodic modulations in many spectral features were found. The
photospheric absorption lines show sinusoidal variations in radial
velocity with an amplitude of km s-1 and a period of
about
. The radial velocities of the narrow emission lines
of He vary with the same period but in anti-phase to the
photospheric lines. The equivalent widths of the narrow emissions
vary with a phase-shift with respect to the velocity curve. The
strength of the red-shifted accretion components of Na D and other
lines is also modulated with the same period. The broad emission
lines of metals vary mostly with the double period of about
.
One unexpected result is that no correlation was found
between the veiling and the brightness, although both parameters varied
in wide ranges. This is partly due to a contribution of the shell
absorption to the photospheric line profiles, which make them vary
in width and depth thus simulating lower veiling.
The spectral lines of the accreting gas show two distinct
components: one is formed at low velocity at the beginning of the
accretion column, and the other at high velocity near the stellar
surface. The low velocity components are strong in low excitation
lines of neutrals, while the high velocity components are strong in
high excitation lines of ions, thus showing the gradients of
temperature and density along the accretion column.
Most of the observed features can be interpreted in the framework of
non-axisymmetric magnetospheric accretion, but the origin of this
asymmetry can be explained in different ways. We consider two
possible models. The first model suggests that RW Aur A is a binary
with a brown dwarf secondary in a nearly circular orbit with a
period of
. The orbiting secondary generates a moving
stream of enhanced accretion from one side of the disk towards the
primary. The other model assumes that RW Aur A is a single star
with a rotational period of
and with two footpoints of
channeled accretion streams within a global magnetosphere which is
tilted relative to the rotational axis or otherwise
non-axisymmetric. Both models can explain qualitatively and
quantitatively most of the observed variations, but there are
some details which are less well accounted for.
Key words: stars: individual: RW Aur A / stars: pre / main sequence / stars: circumstellar matter / accretion / stars: variables
© ESO, 2001
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