Issue |
A&A
Volume 516, June-July 2010
|
|
---|---|---|
Article Number | A19 | |
Number of page(s) | 11 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361/200913743 | |
Published online | 18 June 2010 |
CO observations of symbiotic stellar systems*
1
Observatorio Astronómico Nacional. Ap 112, 28803 Alcalá de Henares, Spain e-mail: v.bujarrabal@oan.es
2
N. Copernicus Astronomical Center, Bartycka 18, 00716 Warsaw, Poland e-mail: mikolaj@camk.edu.pl
3
Observatorio Astronómico Nacional (IGN), Alfonso XII N°3, 28014 Madrid, Spain e-mail: j.alcolea@oan.es
4
Instituto de Radioastronomía Milimétrica (IRAM), Avda. Divina Pastora 7, 18012 Granada, Spain e-mail: quintana@iram.es
Received:
26
November
2009
Accepted:
23
February
2010
Aims. We have studied the molecular content of the circumstellar environs of symbiotic stellar systems, in particular of the well know objects R Aqr and CH Cyg. The study of molecules in these stars will help for understanding the properties of the very inner shells around the cool stellar component from which molecular emission is expected to come.
Methods. We performed mm-wave observations with the IRAM 30 m telescope of the 12CO J = 1-0 and J = 2-1, 13CO J = 1-0 and J = 2-1, and SiO J = 5-4 transitions in the symbiotic stars R Aqr, CH Cyg, and HM Sge. The data were analyzed by means of a simple analytical description of the general properties of molecular emission from the inner shells around the cool star. Numerical calculations of the expected line profiles were also performed that took the level population and radiative transfer under such conditions into account.
Results. Weak emission of 12CO J = 1-0 and J = 2-1 was detected in R Aqr and
CH Cyg and a good line profile of 12CO J = 2-1 in R Aqr was obtained. The
intensities and profile shapes of the detected lines are compatible
with emission coming from a very small shell around the Mira-type
star, with a radius comparable to or slightly smaller than the
distance to the hot dwarf companion, 1014-2×1014 cm.
We argue that other possible explanations are improbable.
This region probably shows properties similar to those
characteristic of the inner shells around standard AGB stars:
outwards expansion at about 5–25 km s-1, with a significant
acceleration of the gas, temperatures decreasing with
radius between about 1000 and 500 K, and densities ~109-3×108 cm-3. Our model calculations are able to explain the asymmetric
line shape observed in 12CO J = 2-1 from R Aqr, in which the
relatively weaker blue part of the profile would result from
selfabsorption by the outer layers (in the presence of a velocity
increase and a temperature decrease with radius). The mass-loss rates
are somewhat higher than in standard AGB stars, as often happens for
symbiotic systems. In R Aqr, we find that the total mass of the CO
emitting region is ~2-3×10-5 ,
corresponding to
~ 5×10-6-10-5
yr-1 and compatible with results obtained from
dust emission. Considering other
existing data on molecular emission, we suggest that the
limited extent of the molecule-rich gas in symbiotic systems is mainly
due to molecule photodissociation by the radiation of the hot dwarf
star.
Key words: radio lines: stars / circumstellar matter / stars: mass-loss / binaries: symbiotic / stars: individual: R Aqr / stars: individual: CH Cyg
© ESO, 2010
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.