LAMBDA CET (Lambda Ceti, the former "Menkar"). Except for those that belong to the brighter or otherwise prominent stars, proper names, while charming, can be problematic if not downright confusing. Many are the duplications. Think first of Deneb, Deneb Algedi, Denebola, Deneb Kaitos, and the multitudinous rest of them. Then there are the real duplications. There is a Gienah in Corvus, another in Cygnus. At least they are in different constellations. Worse are the numerous stars WITHIN a constellation that share a name. Zeta and Epsilon Aquilae are both "Deneb al Okab," a situation moderated by respectively calling them "Australis" and "Borealis." Then there are Lambda and Alpha Ceti, both within the head of Cetus, the Whale or Sea Monster. Rather faint fifth magnitude (4.70) Lambda was the original "Menkar," which from Arabic refers to the Beast's nostrils. Someone in medieval times, however, took it upon himself to transfer the name to brighter, nearly-second-magnitude Alpha, which is in Cetus's jaw. The wrongful title stuck, and Lambda lost out. Alpha, whether properly of not, is "Menkar." The long story rather makes up for the relative lack of knowledge about the star itself, which falls in league in the neglected category with Beta Equulei and Beta Piscis Austrini. And rather too bad. As a relatively hot (13,400 Kelvin) class B (B6) giant (but see below) 576 light years away (give or take 18), it's rather out of place, as it is well off the path of the Milky Way, the natural home of youthful class B stars. And it's really quite an impressive star (surely deserving of keeping its more ancient mythological title) with a total luminosity (including a lot of ultraviolet radiation and a small ten-percent correction for interstellar dust) 920 times that of the Sun. From temperature and brightness, we find a radius of just 5.4 solar, not much for a "giant,' an ill- determined projected rotation speed of 128 kilometers per second (appropriate for the class) yielding a rotation period of under two days. Theory gives an impressive mass between 4.5 and 4.8 Suns (depending on exact details of internal structure) and shows the star to be more a subgiant (one that has given up, or soon will give up, core hydrogen fusion). Youthful indeed, the star is only 100 to 125 million years old. Its fate is to become a fairly white dwarf of about 0.85 solar masses (white dwarfs the cores of the once far more massive stars), massive for such a leftover remnant, but not quite up to the classic example, Sirius B.
Written by Jim Kaler 1/22/10. Return to STARS.