NASHIRA (Gamma Capricorni). Though Capricornus is a relatively faint constellation, its
stars are arranged to make a rather prominent figure. Across the
top are four reasonably bright stars that claimed Bayer's first
four Greek letters, Alpha (Algedi)
through Delta (Deneb Algedi). Bayer
seems to have used position more than brightness, as Delta is
easily the brightest of them. Nashira, the Gamma star, at bright
fourth magnitude (3.68), comes in fourth. The meaning of the
Arabic name is unknown. At one time it was applied to both the
Gamma and Delta stars (which appear to lie close together in the
sky), but is now applied to Gamma alone. For a star so reasonably
bright, Nashira has a rather checkered classification history. It
has been traditionally listed as a class F (F0) star whose
evolutionary status is uncertain, and was by default considered a
main sequence dwarf, one that like the Sun quietly fuses hydrogen
into helium in its deep core. However better observations now
suggest a white class A (A7) star. That and the star's distance of
139 light years allows a calculation of luminosity, showing it
radiate 47 times more energy than the Sun.
The combination of the star's 7950 Kelvin temperature and the
luminosity reveal a mass of 2.5 times that of the Sun and show
Nashira most likely to be a nascent giant star, one that has
stopped its internal hydrogen fusion or is very close to doing so.
Nashira seems to be rotating slowly, only 30 kilometers per second
(or more) at the equator. That is 15 times greater than the solar
rotation speed, but still small compared to the common much more
rapid speeds of class A (and hotter) stars. Relatively slow
rotation means less atmospheric stirring and a possible separation
of elements (some kinds of atoms falling inward, others lofted
outward), and indeed Nashira seems to be classified as "metallic-
line star," though there has been no in-depth study of it. Few of
the "facts" about the star are secure. If nothing else, Nashira
shows that we still have a great deal to learn about even modestly
bright stars that are prominent parts of their constellations.