UPS PER (Upsilon Persei) = 51 AND (51 Andromedae).
The constellations provide a good background
for the initial naming and cataloging of
stars, but in the long run are insufficient. Proper names (Betelgeuse, Altair) are fine as far as they go, but who can
remember thousands, especially when many are so similar to one another.
The first person to bring some order out of the chaos was Johannes
Bayer, who in his Uranometria of 1602 gave the brighter stars Greek letters attached to the Latin genitives
of the constellation names, with the stars ordered by apparent
brightness, location, perhaps whimsy. He was followed by John Flamsteed, the first Astronomer
Royal, who published his great atlas of 2935 stars in 1725, to which
numbers had already been applied to the stars from west to east within
the relevant constellation by Newton and Halley. Vega is thus Alpha Lyrae and also 3 Lyrae. As
expected the schemes were not without problems. Other astronomers had
to complete the work for stars in the far southern hemisphere, and they
did not always agree. Bayer also let several individual stars do double
duty to complete the outlines of adjoining constellations. Alpha Andromedae is also Gamma Pegasi and
Beta Tauri is Gamma Aurigae. (the first of
the pairs always the ones used). Constellation boundaries were also
individualistic and flexible, and could differ considerably from one
astronomer to another. When Eugene Delporte's modern rectangular
boundaries were adopted by the International Astronomical Union in
1930, quite a few Flamsteed stars were orphaned into the wrong
constellation despite Delporte's heroic attmpts to keep everything in
order. Thus Beta Scuti is 6 Aquilae, 3
Arietis is in Pisces, and Gamma Scorpii is also 20 Librae as well as
being Sigma Lib. Various astronomers from Ptolemy onward played around
with 51 Andromedae, which is also Upsilon Persei in northwestern Perseus. Even though the fairly bright fourth
magnitude star (3.57, nearly third) is actually within the confines
of Andromeda, it still goes by the name
Upsilon Per in the modern literature. Sometimes it's best to use a
catalogue that's free of the constellations altogether and just
numbers stars to the east from the Vernal
Equniox. Beyond that bit of arcane history, Ups Per is not terribly
special. At a distance of 111 light years (give or take just 1), Upsilon
is yet another class K (K3) helium-fusing giant like so many others
that populate the sky. With a temperature of 4380 Kelvin (much of its
radiation in the infrared),
Upsilon Per shines with the light of 164 Suns,
from which we derive a radius of 22.3 times solar and a mass of roughly
double solar. Interferometer measures give discordant radii: 22.0
times that of the Sun at visual wavelengths, but 28.6 solar in the deep
red. It's quite possible that both are correct, or close to it, as
stars, being gaseous, can easily have different opacities (and thus
different apparent radii) as measured in different colors. A projected
equatorial rotation velocity of 5.9 kilometers per second suggests a
rotation period as long as 190 days. Two names it may have, but the
star itself seems decidedly single with no companion following along.
(Thanks to "Lost Stars," M. Wagman, McDonald and Woodward,
Blacsksburg, VA ,for discussion, and to Martin Trevisan for suggesting
this star.)
Written byJim Kaler 05/05/17. Return to STARS.