Alpha Trianguli - Metallah, Caput Trianguli

At magnitude 3.41, Alpha Trianguli is the second-brightest star in the ancient constellation Triangulum - a long, thin triangle of stars between Aries and Andromeda. Alpha Trianguli has the traditional Arabic names Metallah or Mothallah ("the triangle") and Ras al Muthallah. In Latin it is referred to as "Caput Trianguli," the "head of the triangle," from its position at the Triangle's sharp southwestern apex.

Mothallah is also a guide to the Triangulum Galaxy, M 33, a dim patch of light lies between Metallah and Mirach in Andromeda. It is galaxy over two million light years away that contains billions of stars, and can be seen with binoculars in a dark sky.

Properties

Metallah is a yellow-white class F6 IV subgiant with a temperature of 6350 K, only 10% hotter than the Sun. From 64 light years away, Metallah shines with 13 solar luminosities, and is three times larger than the Sun. Metallah is a 1.5 solar mass subgiant, more evolved than the Sun, that is close to shutting down its core hydrogen fusion. Yet because stars of higher mass live shorter lives, Metallah is only about 2.7 billion years old.

Metallah is an astrometric binary, accompanied by a small companion with a very short period of only 1.74 days. The separation between them must be only 0.04 AU; other than this, nothing is known about it.

[Adapted from STARS by Jim Kaler, Professor Emeritus of Astronomy, University of Illinois]