ALPHA LAC (Alpha Lacertae). Lacerta, the
Lizard, one of the dimmest constellations of the sky, is a modern
figure ("modern" referring here to the 17th century) invented to
fill in the relative blank area between bright Cygnus, Cassiopeia, and Andromeda. Lacerta's brightest star,
appropriately given Alpha but otherwise quite un-named, is only
fourth magnitude (3.77), which is rather odd for a constellation
that lies within the confines of the Milky Way. Alpha Lac is among
the more common of naked-eye stars, a white class A (A1) hydrogen-
fusing dwarf. Just over 102 light years away, Alpha Lac gives us
a chance to see what our brightest star Sirius would look like if it were a dozen
times more distant. With a temperature of 9200 Kelvin, Alpha Lac
shines with a radiance 27 times that of the Sun, its radius double solar. Unlike many
class A stars, which have odd chemical anomalies that are the
result of diffusion of the elements in quiet atmospheres (some
settling down under gravity, others raised by the pressure of
radiation, exemplified by Alpheratz,
Elnath, and Mizar), Alpha Lac is "normal," the result of
a high rotation speed that keeps things stirred up. Spinning at
least 146 kilometers per second at the equator, the star makes a
full rotation in under 17 hours. At first glance, Alpha Lac seems
to have a companion, a dim twelfth magnitude (11.8) star located 36
seconds of arc away. Alas, the pairing is only line-of-sight. Not
only are the two separating from each other much too quickly for
the motion to be orbital, but spectroscopy of the "companion" shows
it to be a class A5 star. To be that dim, the star must have a
distance of 2700 light years, nearly 27 times farther than Alpha
Lac proper. The "lack" (no pun intended) of an orbiting companion
means we have to calculate Alpha Lac's mass and status from its
luminosity and temperature. Just over twice the solar mass, the
star is fairly young, and not all that long ago began its billion-
year stable hydrogen-fusing lifetime, after which it will become a
red giant and then a far- dimmer white dwarf like the true
companion to Sirius.