Arcsecond-resolution 12CO mapping of the yellow hypergiants IRC +10420 and AFGL 2343
Abstract
Context: IRC +10420 and AFGL 2343 are the unique, known yellow hypergiants (YHGs) presenting a heavy circumstellar envelope (CSE).
Aims: We aim to study the morphology, exceptional kinematics, and excitation conditions of their CSEs, and the implications for mass-loss processes.
Methods: We have mapped the 12CO J=2{-}1 and 1-0 emission in these YHGs with the IRAM Plateau de Bure interferometer and the 30 m telescope. We developed LVG models in order to analyze their circumstellar characteristics.
Results: The maps show that the overall shape of both CSEs is approximately spherical, although they also reveal several aspherical features. The CSE around IRC +10420 shows a rounded extended halo surrounding a bright inner region, with both components presenting aspherical characteristics. It presents a brightness minimum at the center. The envelope around AFGL 2343 is a detached shell, showing spherical symmetry and clumpiness at a level of 15% of the maximum brightness. The envelopes expand isotropically at 35 km s-1, about two or three times faster than typical CSEs around AGB stars. High temperatures ( 200 K) are derived for the innermost regions in IRC +10420, while denser and cooler ( 30 K) gas is found in AFGL 2343.
Conclusions: The mass-loss processes in these YHGs have been found to be similar. The deduced mass-loss rates ( 10-4{-}10-3 M⊙ yr-1) are much higher than those obtained in AGB stars, and they present significant variations on time scales of 1000 yr.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- April 2007
- DOI:
- 10.1051/0004-6361:20066169
- arXiv:
- arXiv:astro-ph/0702400
- Bibcode:
- 2007A&A...465..457C
- Keywords:
-
- stars: circumstellar matter;
- stars: mass-loss;
- radio lines: stars;
- stars: individual: IRC +10420&;
- stars: individual: AFGL 2343;
- Astrophysics
- E-Print:
- Astron.Astrophys.465:457-467,2007