The COSAS survey I: First results from the IRAM mapping survey of 12CO J=1-0 & J=2-1 emission in AGB and early post-AGB circumstellar envelopes
Abstract
Here we present the first result from the COSAS (CO Survey of late AGB Stars) program (P.I. A. Castro-Carrizo), a J=1-0 and J=2-1 line emission mapping survey of a statistically representative sample of circumstellar envelopes around AGB and post-AGB stars. This mapping survey has been carried out to investigate the small and large scale morphological and kinematical properties of the molecular environment surrounding stars in the late AGB and early post-AGB phases. For this, COSAS ideally combines the high spatial resolution and sensitivity of the IRAM Plateau de Bure Interferometer, with the IRAM Pico de Veleta 30m-MRT capabilities to map more extended emission. The whole program includes of 45 stars, selected to sample a wide variety in mass loss rate, chemical type (M, S and C types), variability type (regular variables like Miras and OH/IRs, semiregulars, irregulars, and non varying post-AGBs), evolutionary state, and initial mass. By no means it is an unbiased sample, so results must be interpreted with care, and in terms of the different population of sources represented in the sample. COSAS products (at first. maps and velocity fields, and after modeling, excitation and density profiles across the envelopes) provides means to quantify variations in the mass-loss rate history, assess on the prevalence of different morphological and kinematical features, and investigate the appearance of fast aspherical winds in the late-AGB and early post-AGB phases. This paper, which is the first of a series of COSAS papers, presents the results from the final mapping of a sample of 16 selected sources (about 1/3 of the whole list), namely: WX Psc, IK Tau, TX Cam, RX Boo, X Her, CRL 2362, x Cyg, V Cyg, S Cep, OH 104.9+2.4, R Cas, IRAS 19475+3119, IRAS 20028+3910, IRAS 21282+5050, IRAS 23321+6545 and CRL 2477. The envelopes around late AGB stars are found to be mostly spherical, but often presenting features like concentric arcs (R Cas and TX Cam), spiral density patterns (TX Cam), molecular high density patches testifying to highly irregular mass-loss process (WX Psc, IK Tau, V Cyg, and S Cep), and yet well-defined axis-symmetric morphologies and kinematical patterns (X Her and RX Boo). The molecular envelopes span a large range of sizes, from the relatively compact cases of CRL 2362, OH 104.9+2.4 and CRL 2477, to very large ones, such as in x Cyg and TX Cam. Self- absorption features are observed in some cases, as in IK Tau and x Cyg, testifying to the emergence of (aspherical?) winds in the innermost circumstellar regions. Strong axial structures with more or less complex morphologies are detected in four, out of five, early post-AGB stars of this first sub-sample (IRAS 20028+3910, IRAS 23321+6545, IRAS 19475+3119, and IRAS 21282+5050).
- Publication:
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Asymmetric Planetary Nebulae 5 Conference
- Pub Date:
- 2011
- Bibcode:
- 2011apn5.confP...5A
- Keywords:
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- planetary nebulae: general