EPS PER (Epsilon Persei). Set with bright Jewel-like stars, Perseus oddly has relatively few with well-
known proper names. Among those missing them are bright third
magnitude (2.89) Epsilon Persei, which lies in the middle of the
eastern of the streams of stars that make the Hero's figure.
Luminous, blue, beautiful, and possibly multiple, this class B
(B0.5) hydrogen fusing dwarf is (at 27,600 Kelvin) among the
hottest stars of the naked-eye sky. At a distance of 538 light
years, and set within the Milky Way, it is subject to a bit of
dimming by interstellar dust. Were there none in the way, Eps Per
would make it almost to second magnitude. This correction, plus a
goodly allowance for ultraviolet radiation from the hot surface,
gives a great luminosity of 24,900 times that of the Sun, from which we derive a radius 7 times
solar. The large mass, 14 times that of the Sun, puts Eps Per well
over the limit of stars that are destined to explode as supernovae. Less than 10
million years old, it has only a few million years left before the
grand event takes place. Though young, the star is slightly
evolved, and has entered the realm of the subtly-unstable "Beta
Cephei stars," which pulsate with multiple periods, the instability
driven by layers deep within the star. Epsilon Persei is also
famed among stellar astronomers as one of the most extreme
"spectrum variables," in which the shapes of the absorptions seen in the spectrum
vary rapidly over multiple periods between 2.27 and 8.46 hours (and
are related to the small brightness variations that the star
undergoes). The minimum equatorial rotation velocity of 134
kilometers per second implies a period less than 2.6 days, while
the spectral oscillations suggest a consistent 1.7 days, leading to
an axial tilt relative to us of about 50 degrees (though the
rotation speed is vigorously argued). Spectral variations also
suggest that Epsilon Per has a close companion with an eccentric
orbit and a 14 day period, which would imply a separation of around
0.3 Astronomical Units (AU). It seems possible, however, that the
pulsations merely fool us into thinking the companion is there.
More real is a class A2 dwarf companion (Epsilon Persei B)
separated from Eps Per proper by about 10 seconds of arc, or at
least 1600 AU, implying a period of at least 16,000 years. The
smaller star's apparent brightness shows that it lies at a distance
similar to Eps Per A, so it is probably a real companion. Farther
out, 78 seconds of arc (at least 13,000 AU) away is Eps Per C. If
a real companion, which seems unlikely, its brightness shows that
it is a class K (K7) dwarf with a period of at least 370,000 years.
It is probably line a line of sight coincidence, the best guess
making Eps Per a visual double.