R Coronae Borealis (RCB) stars are evolved, hydrogen deficient, carbon rich stars,
which show sporadic spectacular declines in optical brightness of the orders of 8 magnitdes
or more on time-scales of weeks. Though these stars have been known for a while now(Ref),
no one seems to have figured out what physical processes can explain the features that are
observed in these rare but enigmatic objects.
In an effort to explain some of these features, and consequently achieve an overall
understanding of the RCB's, i intend to study a peculiar feature in the RCB spectrum, the
Helium 10830 line.
As mentioned RCB stars are highly evolved, H-deficient, C-rich stars, known for a long time,
which show spectacular declines in their optical brightness on time scales of a few weeks. They are
relatively rare, and only abt 30 are known in the galaxy.
In general, there exist 2 models for these stars which researchers in the field seem to favour.
In general, though there is some consensus on the following... the decline is caused due to formation
of a carbon-rich dust cloud along the line of sight (LoS) which initially obscures the protosphere of the star.
This reveals the surrounding chromospheric spectrum, rich in emission lines. The emission lines are primarily
low level neutral or singly ionized lines, but some 'hot' lines like HeI 10830 are also seen. Whats interesting is
the P-Cygni profile of this particular line. The following questions need to be addressed...