Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004apj...617.1142s&link_type=abstract
The Astrophysical Journal, Volume 617, Issue 2, pp. 1142-1156.
Astronomy and Astrophysics
Astronomy
28
Stars: Circumstellar Matter, Ism: Planetary Nebulae: Individual: Alphanumeric: Crl 618, Ism: Reflection Nebulae, Stars: Agb And Post-Agb, Stars: Mass Loss, Stars: Winds, Outflows
Scientific paper
We present 1" resolution interferometric maps of the CO J=2-1 and HC3N J=25-24 emission in the protoplanetary nebula CRL 618 obtained with the millimeter array of the Owens Valley Radio Observatory (OVRO). Our CO data trace with high accuracy the spatio-kinematic structure of different molecular components: (1) the fast, bipolar outflow, which is observed up to axial distances of +/-2.5" (+/-2.7×1016 cm) from the nebula center with a maximal deprojected expansion velocity of Vexp~340 km s-1 (2) the roughly round outer halo, which is slowly expanding at Vexp~17 km s-1 (3) an extended structure that is elongated in the polar direction +/-6" (+/-8.1×1016 cm), surrounding the optical lobes, and that expands at Vexp~22 km s-1 (slow axial component); and (4) a dense, inner torus-like core (Rout~1.6×1016 cm) expanding at Vexp<~12 km s-1. Components (3) and (4) have been revealed for the first time by our high angular resolution data. The geometry, kinematics, density, and temperature distribution of the individual components of the molecular envelope of CRL 618 have been constrained by fitting a spatio-kinematic model to the data. We interpret our results in terms of nebular evolution as follows. In the last >~2500 yr, there have been at least two distinct episodes of mass loss at a large scale in the form of a slow wind. The first took place at a rate of M<~10-5 Msolar yr-1 and gave place to the tenuous outer halo. The second mass-loss event started ~400 yr ago at a higher rate of M~10-4 Msolar yr-1, resulting in the formation of the inner dense core. More recently, the interaction between fast axial post-asymptotic giant branch (AGB) winds and the preexisting circumstellar envelope has shaped (i) the fast bipolar outflow, which is probably composed of shocked material that was originally in the inner dense core, and (ii) the slow axial component, which could represent material in the interface between the shocked and unshocked AGB envelope. Finally, we report a recent increase of the free-free continuum emission at 1.3 mm (2.1+/-0.3 Jy) and 3 mm (2.3+/-0.3 Jy), which could reflect changes in the activity of the fast post-AGB winds on a timescale of a few years.
Alcolea Javier
Bujarrabal Valentin
Castro-Carrizo Arancha
Sanchez Contreras Carmen
Sargent Anneila
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