ALPHA LYN (Alpha Lyncis) and ALSCIAUKAT (31 Lyncis). In the far
northern sky stalk three faint animals, modern constellations that
hardly anyone points out, Camelopardalis
(the Giraffe), Lacerta (the Lizard), and
long straggly Lynx, the eponymous Lynx.
Two stars oddly stand out, and they are so remarkably similar that
they deserve to be taken together. The third magnitude (3.16)
luminary by far tops the brightness list, well-deserving its Greek letter designation. Alpha is also the
constellation's ONLY star that carries a Greek letter! Most of the
other stars that form Lynx use Flamsteed numbers, including 31
Lyncis, which at fourth magnitude (4.26) is also fourth in
brightness. Oddly, 31 Lyncis is the only star that carries a
proper name, jaw-breaking "Alsciaukat," which comes to us from
ancient Arabic lore and refers to a "thorn." The similarity of the
stars is amazing, yet like identical twins there are subtle
differences as well. Alpha Lyn is brighter because it is closer,
220 light years, as opposed to 31 Lyn, which is 390 light years
away. A class K (K7) giant, Alpha (3860 Kelvin) is also slightly
cooler than the class K (K4.5) giant (3930 Kelvin) 31 Lyn. (The
temperatures are not known really all that well). When we take
infrared radiation into account, the luminosities are nearly
identical, 700 Suns for Alpha, 740 for "31."
From their temperatures and luminosities, Alpha is 59 solar
diameters across, as is "31"! Direct measure of angular diameter
gives respective values of 65 and 75, suggesting that some of the
parameters for "31" are in error. Both weigh in at around two
solar masses and have metal contents that are either like that of
the Sun or just a bit lower. It is difficult to know whether they
are becoming brighter giants with dead helium cores, dimming a bit
with helium cores fusing into carbon and oxygen, or brightening
with dead carbon cores and preparing to slough off their outer
envelopes. They may in fact each be in different stages.
Nevertheless, each is around 1.4 billion years old, and gave up
core hydrogen fusion about 300 million years ago. Alsciaukat ("31"
is so much easier) has the distinction of being a variable star,
and as such is also known as BN Lyncis (the double Roman letter always
denoting variability). But not by much, the variation a subtle
0.05 magnitudes (about 5 percent). The variability, however, is a
tipoff that the star is indeed becoming a brightening giant for the
second time with a dead carbon core, and will shortly turn into a
long-period variable like Mira. The
coincidence within this obscure constellation is quite remarkable,
yet even with characteristics this close, the stars are true
individuals. Thanks to Shawn Urban, who suggested 31 Lyncis.