4.6 Article

HI and CO in the circumstellar environment of the S-type star RS Cancri

Journal

ASTRONOMY & ASTROPHYSICS
Volume 515, Issue -, Pages -

Publisher

EDP SCIENCES S A
DOI: 10.1051/0004-6361/200912731

Keywords

stars: individual: RS Cancri; stars: mass-loss; stars: AGB and post-AGB; stars: winds, outflows; radio lines: stars; circumstellar matter

Funding

  1. INSU/CNRS (France)
  2. MPG (Germany)
  3. IGN (Spain)

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Context. The history of mass loss during the AGB phase is key to understanding the stellar evolution and the gas and dust replenishment of the interstellar medium. The mass-loss phenomenon presents fluctuations with a wide variety of timescales and spatial scales and requires combining data from multiple tracers. Aims. We study the respective contributions of the central source and of the external medium to the complex geometry of circumstellar ejecta. Methods. This paper presents Plateau de Bure Interferometer and IRAM 30-m telescope CO rotational line observations, along with HI data obtained with the Nan ay Radio Telescope for the oxygen-rich semi-regular variable RS Cnc, in order to probe its circumstellar environment on different scales. Results. We detect both the CO(1-0) and the CO(2-1) rotational lines from RS Cnc. The line profiles are composite, comprising two components of half-width similar to 2 km s(-1) and similar to 8 km s(-1), respectively. Whereas the narrow velocity component seems to originate in an equatorial disk in the central part of the CO envelope, the broad component reveals a bipolar structure, with a north-south velocity gradient. In addition, we obtain new HI data on the source and around it in a field of almost 1 square degree. The HI line is centered on v(LSR) = 7 km s(-1) in agreement with CO observations. A new reduction process reveals a complex extended structure in the northwest direction, of estimated size similar to 18', with a position angle (similar to 310 degrees) opposite the direction of the stellar proper motion (similar to 140 degrees). We derive an HI mass of similar to 3 x 10(-2) M(circle dot) for this structure. Based on a non spherical simulation, we find that this structure is consistent with arising from the interaction of the star undergoing mass loss at an average rate of similar to 10(-7) M(circle dot)yr(-1) over similar to 2-3 x 10(5) years with the interstellar medium. Conclusions. Using CO and HI lines, we show that the circumstellar environment around RS Cnc includes two related but well separated regions. With CO, we find a bipolar geometry that probably originates from the intrinsic behavior of recent mass-loss processes. With HI, we find a trail of gas, in a direction opposite to the proper motion of RS Cnc lending support to the hypothesis of an interaction with the interstellar medium. This work illustrates the powerful complementarity of CO and HI observations with regard to a more complete description of circumstellar environments around AGB stars.

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