From jkaler@shout.net Wed Mar 14 11:16:09 2001 Date: Wed, 14 Mar 2001 11:14:10 -0600 From: Jim Kaler To: kaler@astro.uiuc.edu [ Part 2: "Attached Text" ] Tureis 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 6 times more energy than the Sun from its 6540 Kelvin surface. As a giant with a mass about 1.5 times that of the Sun, it has recently (or will soon) shut down its internal hydrogen fusion. Tureis, otherwise quite ordinary, makes its mark as one of the sky's brightest "Delta Scuti" variable stars. 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 Mekbuda in Gemini. Having lower masses, luminosities, and radii than classical Cepheids (Tureis only twice the solar size), 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 believe that the star had a close companion, but that is no longer believed. Though Tureis is only 6 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 encircling 14th magnitude neighbor about which little is known. Lying at least 570 astronomical units away (14 times Pluto's average distance from the Sun), this (probable) class M5 red dwarf (similar to Proxima Centauri) takes a minimum of 10,000 years to orbit, if in fact the two are connected at all. ^Z [ Part 3: "Attached Text" ]