The Caldwell Objects

NGC 2867 is a nitrogen-rich planetary nebula; its
nitrogen abundance is 1.6 times greater than that
found in our Sun. Excess nitrogen in planetaries
is created when carbon is destroyed in nuclear
reactions; this takes place when the nebula's
precursor star starts out with 3 to 11 solar masses.
Spectra of NGC 2867 also have shown it to have
more carbon (per unit of hydrogen) than our Sun
contains. The carbon and nitrogen both may have
been dredged up by an episode of convection late
in the star's life, when carbon, oxygen, and nitrogen
were catalyzing the fusion of hydrogen into
helium. On the other hand, spectroscopic
observations from the Anglo-Australian Telescope
and the International Ultraviolet Explorer
satellite show no significant chemical-abundance
abnormalities. That being said, in 1998 Walter
Feibelman did describe a rich variety of
90
previously unreported emission lines in the IUE
spectrum of the nebula and its central star. That
star, by the way, is a 15th-magnitude Wolf-Rayet
star of sorts; it has a spectrum similar to the much
more massive Wolf-Rayets like HD 192163 in
NGC 6888 (Caldwell 27). NGC 2867's nebulous
shell is believed to contain 20 or 30 percent as
much mass as our Sun and (as seen from Earth
today) to be about 3,000 years old.
Just over the border in Vela, 1½° northeast of
NGC 2867 and 30' west of the star Ν Carinae, is
the 6th-magnitude (my estimate) open cluster IC
2488 — a splash of 9th- to llth-magni-tude stars
that look like a drooping bow tie. And just a little
less than 1° due south of Kappa (κ) Velorum, the
northeastern tip of the False Cross, is the bright
binocular variable V Velorum, a classical Cepheid
whose brightness fluctuates between magnitude
7.2 and 7.9 every 4.37 days.
The Caldwell Objects 357