TUREIS (Rho Puppis). Within the great ship Argo, in which Jason sailed to find the golden fleece,
is a group of stars that represents a "little shield." The term
was erroneously applied in Greek to the star Aspidiske (Iota Carinae) and then in
Arabic to the star we now know as Rho Puppis (Carina the hull of the ship, Puppis the stern). Lying rather prominently to the
west of Wezen in Canis Major, Tureis shines at an easily-visible third
magnitude (2.81), and is one of the most northerly of the brighter
stars of the constellation. From its
distance of only 63 light years, this yellow-white class F (F6) giant star radiates 22 times more
energy than the Sun from its 6540 Kelvin surface. Temperature and
luminosity then yield a radius of 3.7 times that of the Sun. An equatorial rotation speed of at least
14 kilometers per second leads to a rotation period under 13 days.
With a mass estimated at 1.85 times that of the Sun, the star has
recently shut down its internal hydrogen fusion, making it more of
a subgiant than a giant. Tureis, otherwise quite ordinary, makes
its mark as one of the sky's brightest "Delta Scuti" variables.
The Delta Scuti stars represent the
low-luminosity tail of the bright giant and supergiant Cepheid variables that in turn
are represented so well by the prototype Delta Cephei and by Mekbuda in Gemini. Having lower masses, luminosities, and radii
than classical Cepheids (Tureis just under twice the solar mass),
they pulsate subtly and quickly. Tureis changes by only about 10%
over a precisely known period of 0.14088143 days (3 hours 22
minutes 52 seconds). Far lesser variations make the star pulsate
at 0.13 and 0.16 days as well. The variations (which influence the
spectrum) once led us to think
that the star had a close companion, but that is no longer
believed. Though Tureis is only 22 times brighter than the Sun, it
is anomalously classed as a far grander "bright giant," which for
unknown reasons is typical of Delta Scuti stars. Among the Delta
Scuti crowd, Tureis closely sets the low-temperature limit. While
having no close companion, it does seem to have a distant 14th
magnitude neighbor 30 seconds
of arc away about which nothing is known. Most likely it is just
a line-of-sight coincidence. If it is in fact a real companion, it
would (from its brightness) to be an M5 dwarf. Lying at least 570
astronomical units away (14 times Pluto's average distance from the
Sun), it would, if real, take a minimum of 10,000 years to orbit.
Only additional observations (there is but one) can tell if the
little one moves in concert with Tureis proper.
Written by Jim Kaler; updated 9/05/08.
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