Mass-Loss Histories of Three Carbon-rich Evolved Stars as Revealed by 12CO Emission

摘要: We investigate the history and geometry of mass loss in three carbon-rich evolved stars, CIT 6, AFGL 618, IRAS 21282+5050, using observations 12CO J = 1-0 line emission a simple radiative transfer code to model these observations. Combining data from Berkeley-Illinois-Maryland Association millimeter array NRAO 12 m, we have constructed full synthesis cubes 21282+5050 with angular resolutions approximately 8'', 3'', 4'', respectively. find clumpy envelopes zero-order structures bright cores, surrounded by lower surface brightness halos all sources; however, contrast between core halo is greater for 618 than 6. The total flux profile 6 has parabolic shape, flat-topped shape found previous single-dish that resolved envelope, which measure be at least 100'' diameter. similar east-west bipolar morphology as its optical reflection nebulosity, although on much larger scale (90'' × 60''). bulk molecular gas participates symmetric expansion; significant outflow appears heart detected velocities up ~70 km s-1. A blueshifted component (~-40 s-1) this observed absorption against continuum source 618. resolve central hole size, 6'', slightly H II region. ring surrounds hole, ~70'' diameter ring. broken position-velocity cuts due self-absorption gas. develop assumes spherically expansion core-halo sources. assume temperature power-law respect radius fit index -0.7 -0.8 fitted density profiles reflect differences suggest mass-loss histories models both are consistent constant rates (6 ± 2) 10-6 4) 10-5 M☉ yr-1, suggests two phases loss: an older asymptotic giant branch (AGB) wind lasting ~8000 yr when rate decreased (2 1) 10-4 (3 yr-1 more recent superwind ~4000 increased yr-1.