Issue |
A&A
Volume 491, Number 3, December I 2008
|
|
---|---|---|
Page(s) | 789 - 796 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:200810089 | |
Published online | 23 September 2008 |
H I and CO in the circumstellar environment of the oxygen-rich AGB star RX Leporis
1
LERMA, UMR 8112, Observatoire de Paris, 61 Av. de l'Observatoire, 75014 Paris, France e-mail: yannick.libert@obspm.fr
2
GEPI, UMR 8111, Observatoire de Paris, 5 place J. Janssen, 92195 Meudon Cedex, France
3
IRAM, 300 rue de la Piscine, 38406 St. Martin d'Hères, France
Received:
29
April
2008
Accepted:
21
August
2008
Context. Circumstellar shells around AGB stars are built over long periods of time that may reach several million years. They may therefore be extended over large sizes (~1 pc, possibly more), and different complementary tracers are needed to describe their global properties.
Aims. We set up a program to explore the properties of matter in the external parts of circumstellar shells around AGB stars and to relate them to those of the central sources (inner shells and stellar atmospheres).
Methods. In the present work, we combined 21-cm H I and CO rotational line data obtained on an oxygen-rich semi-regular variable, RX Lep, to describe the global properties of its circumstellar environment.
Results. With the SEST, we detected the CO(2–1) rotational line from RX Lep.
The line profile is parabolic and implies an expansion velocity of
~4.2 km s-1 and
a mass-loss rate ~1.7 10-7
yr-1
(
pc). The H I line at 21 cm was detected with the Nançay
Radiotelescope on the star position and at several offset positions.
The linear shell size is relatively small, ~0.1 pc, but
we detect a trail extending southward to ~0.5 pc.
The line profiles are approximately Gaussian with an FWHM ~ 3.8 km s-1
and interpreted with a model developed for the detached shell around the
carbon-rich AGB star Y CVn. Our H I spectra are well-reproduced by assuming a
constant outflow (
= 1.65
10-7
yr-1) of ~4
104 years duration, which has been
slowed down by the external medium.
The spatial offset of the H I source is consistent with the northward
direction of the proper motion
measured by Hipparcos, lending support to the presence of a trail resulting
from the motion of the source through the ISM, as already suggested for
Mira, RS Cnc, and other sources detected in H I . The source was also observed
in SiO (3 mm) and OH (18 cm), but not detected.
Conclusions. A detached shell, similar to the one around Y CVn, was discovered in H I around RX Lep. We also found evidence of an extension in the direction opposite to the star proper motion. The properties of the external parts of circumstellar shells around AGB stars should be dominated by the interaction between stellar outflows and external matter for oxygen-rich, as well as for carbon-rich, sources, and the 21-cm H I line provides a very useful tracer of these regions.
Key words: stars: individual: RX Lep / stars: mass-loss / stars: AGB and post-AGB / stars: winds, outflows / radio lines: stars / stars: circumstellar matter
© ESO, 2008
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