Filling the missing link of planetary nebula formation: A millimeter interferometric and mid-IR imaging study of evolved stars

Details Filling the missing link of planetary nebula formation: A millimeter interferometric and mid-IR imaging study of evolved stars Filling the missing link of planetary nebula formation: A millimeter interferometric and mid-IR imaging study of evolved stars

Jan 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993phdt........44m&link_type=abstract

PhD Dissertation, California Univ. Berkeley, CA United States

Astronomy and Astrophysics

Astronomy

13

Planetary Nebulae, Astronomical Interferometry, Planetary Evolution, Infrared Astronomy, Asymptotic Giant Branch Stars, Millimeter Waves, Stellar Mass, Halos, Stellar Winds, Carbon, Interplanetary Dust

Scientific paper

The mass loss mechanism, which drives intermediate mass stars (0.8-8 solar mass) from the asymptotic giant branch (AGB) to the planetary nebula (PN) stage, is poorly understood. Indeed, there is a 'missing link' in our knowledge of planetary nebula formation between the AGB and PN phases, often referred to as the proto-planetary nebula phase (PPN). In this thesis, we present a mid-IR (8-13 micrometer) imaging study of 48 AGB stars, PNe and PPNe for which we used the Berkeley/IGPP/ LEA mid-IR array camera, and a millimeter interferometric mapping study of the CO J = 1-0 line in three evolved stars for which we used the Berkeley-Illinois-Maryland mm-Array (BIMA). The four most important conclusions of this study follow. Our complete CO map of CIT6 shows two components to the mass loss envelope in CIT6: a core wind and a halo. The core wind has a kinematic structure expected for an almost spherically symmetric, constant velocity outflow. The halo has a puzzling kinematic structure that covers the same velocity range as the core wind, but unlike the core wind, it has the same spatial scale at all velocities. The circumstellar dust nebulae surrounding the PPNe are characterized by thin, limb brightened shells with elliptical, toroidal or extreme bipolar structures indicating that the last stage of AGB mass loss is inherently aspherical, short lived and very intensive. We claim that these mid-IR images form the first clear and direct observational evidence of superwinds. An evolutionary sequence of five carbon rich objects clearly traces the origin of bipolarity in carbon rich PNe to this superwind stage. We derive an average dynamical age for F-G spectral type PPNe to be approximately 220 years, with an upper limit of less than 400 years and an average dynamical age of approximately 290 years for the young PNe that we imaged. These short timescales favor stellar evolutionary models that incorporate mass loss in the post-AGB evolution. The dust in mid-IR bright young PNe is heated primarily by direct stellar radiation and not Ly-alpha which dominates the dust heating in more evolved PNe.

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