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. Return to STARS.