| Issue |
A&A
Volume 475, Number 2, November IV 2007
|
|
|---|---|---|
| Page(s) | 559 - 568 | |
| Section | Interstellar and circumstellar matter | |
| DOI | https://doi.org/10.1051/0004-6361:20078198 | |
| Published online | 02 October 2007 | |
Mass loss from dusty, low outflow-velocity AGB stars *,**
II. The multiple wind of EP Aquarii
1
IRAM, 300 rue de la Piscine, 38406 St. Martin d'Hères, France e-mail: winters@iram.fr
2
LERMA, UMR 8112, Observatoire de Paris, 61 Av. de l'Observatoire, 75014 Paris, France
Received:
2
July
2007
Accepted:
31
August
2007
Context.CO rotational lines are frequently used to trace the outflows from AGB stars. Some profiles are composite, with a narrow component super-imposed on a broader one. These profiles have been interpreted in different ways, calling for episodic mass loss, a bipolar flow, or a circumstellar disk.
Aims.To investigate the structure of one of these outflows, we have obtained detailed 12CO(2–1) and 12CO(1–0) maps of EP Aqr, a prototypical source with composite CO profiles.
Methods.Interferometric data were acquired with the IRAM interferometer
and combined with on-the-fly maps obtained at the IRAM 30-m. The
resulting maps in 12CO(2–1) and 12CO(1–0) cover a field of
with a spectral resolution of
0.1 km s-1 and with beams of 
and 
, respectively.
Results.The source is clearly resolved with a size of about 
(FWHM). We do not observe any obvious departure from circular
symmetry, but there is evidence of a ringed structure in the
CO(2–1) map with enhanced intensity at ~
and
from the central star. The continuum level at 1.3 and
2.6 mm is consistent with the star's photospheric emission. We
modeled the spatio-kinematic structure with Monte-Carlo radiative
transfer simulations assuming spherical symmetry. We reached a
reasonable fit to the map-integrated spectra, but not to the imaging
data, possibly because the circumstellar shell of EP Aqr presents
inhomogeneities on a scale that is not, or is only barely, resolved in our
maps. EP Aqr may be a proto-typical oxygen-rich source for the
class of theoretical models exhibiting mass loss variations on a
~100 yr timescale discovered by Winters et al. (2000), which
show a layered structure in their extended circumstellar shells.
Key words: hydrodynamics / stars: mass-loss / stars: AGB and post-AGB / stars: winds, outflows / radio lines: stars / circumstellar matter
© ESO, 2007
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.