Abstract
A set of high-resolution 2 microns infrared spectral observations of the
prototype obscured carbon star IRC+10216 have been modeled using a
co-moving frame-of-reference formalism and monotonic spherically
symmetric gas flow. The data set spans more than a decade and shows that
the line profile shapes of the CO (0-2) overtone band transitions have
changed during the period of observation. Preliminary results indicate
that these lines are formed within 15 stellar radii (R_*) of the central
star and suggest an evolution of this inner section of the circumstellar
shell over a time span of a few years. This supports recent ideas which
argue against constant outflow models for mass loss in evolved stars.
The presented gas models required to fit the data show distinct
phenomena: 1) An abrupt acceleration of the gas flow (Delta v ~ 10 km
s(-1) ) is located in approximately the same region where the dust
condensation occurs in the model (2.5 to 5 R_*). This observation is
consistent with theories which predict that dust grains, accelerated by
radiation pressure from the central star, drag the gas molecules
outward. 2) A region of almost constant velocity located just past the
dust condensation point (5 R_*) slowly accelerates from about 10.5 km
s(-1) to the terminal expansion velocity of the shell (14.2 km s(-1) at
12 R_*). The evolution of the line profile shapes during the 12 years
spanned by the data require this velocity plateau to expand radially by
about 4 R_*. In contrast with the 1.75 year period of pulsation of the
central star, these variations in the line profiles suggest a rate of
evolution for the inner envelope of the circumstellar shell on the order
of decades.
Original language | English |
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Journal | American Astronomical Society, 181st AAS Meeting |
Volume | 181 |
Publication status | Published - 1 Dec 1992 |
Externally published | Yes |