Volume 475, Number 2, November IV 2007
|Page(s)||559 - 568|
|Section||Interstellar and circumstellar matter|
|Published online||02 October 2007|
II. The multiple wind of EP Aquarii
IRAM, 300 rue de la Piscine, 38406 St. Martin d'Hères, France e-mail: email@example.com
2 LERMA, UMR 8112, Observatoire de Paris, 61 Av. de l'Observatoire, 75014 Paris, France
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
Based on observations carried out with the IRAM Plateau de Bure Interferometer and the IRAM 30 m telescope on Pico Veleta. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).
© 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.