LAMBDA AND (Lambda Andromedae). Radiating at just under third
magnitude (3.52), Lambda Andromedae is modestly bright, but it is
so far north of the major part of the outline of the constellation
Andromeda that it hardly seems a
part of it, and is thereby largely ignored by the backyard
observer. Not, however, by the research astronomer, as
Lambda And
is a rather unusual critter, one of the brightest "RS Canum
Venaticorum" (RS CVn) variable stars in the sky. Glowing as a
"yellow" class G (G8) 4900 Kelvin giant-subgiant, Lambda And
resides at a relatively nearby distance of 84 light years. A "spectroscopic" double, its
companion, which cannot be directly detected, orbits with a period
of 20.5212 days, the bulk of the light coming from the primary star
itself, which shines with the light of 22 Suns, the star's radius 6.5 times solar. These
parameters give us a mass close to double solar. About a billion
years old, with a now-dead helium core, the star is now making its
transition to becoming a true giant. Taking a wild guess at the
companion's mass, say equal to that of the Sun, the separation
between the two would be only 0.24 Astronomical Units (AU). Like
others of the "RS CVn" class, the two stars of Lambda interact
tidally (a tide being a gravitational stretching effect) to affect
each others' rotations. Rotation and convection in the Sun cause
concentrations of magnetic fields that give rise to sunspots and
related magnetic and thus starspot activity. The interaction in
Lambda (and other RS CVn stars) causes increased rotation and thus
vastly enhanced magnetic activity that gives it a powerful outer
corona with temperatures that range between 10 and 40 million
Kelvin (as compared with the Sun's 2 million Kelvin corona). As a
result of either huge starspots or bright active zones that swing
in and out of sight, Lambda varies by about a tenth of a magnitude
with its rotation period of 54 days. Lambda And is a "long period"
RS CVn star, an unusual one in that the orbital and rotation
periods are not synchronized such that the two stars always face
each other. Apparently, the companion is still "spinning up" the
larger giant via tidal action. There is also some evidence for a
long activity cycle akin to the solar 11 year cycle, one that lasts
from 5 to 14 years. Lambda has two other facets that recommend it.
Intense magnetic activity makes it visible to radio telescopes. As
a result it is one of the stars that can help correlate precise
radio coordinate positions of celestial objects with optical
positions of stars made by satellite. The double that makes Lambda
And proper is also surrounded by a quartet of low mass class M
dwarfs that make something of a double-double with the bright star
(at least as long as there are no line-of-sight coincidences
involved). 48 seconds of arc (at least 1300 AU) away is a 13th
magnitude component that would take at least 25,000 years to orbit.
217 seconds (at least 5600 AU) away is a pair of 11th magnitude M
stars separated by 69 seconds that would take at least 96,000 years
to orbit each other, the outer double taking at least 200,000 years
to go around the inner trio, the whole system a fascinating
quintuple star.