37 and 39 TAU (37 and 39 Tauri), a two for one special.
Halfway between the Hyades and Pleiades of Taurus lies a pair of unequal stars that is
something of a faint version of Mizar and Alcor in the Big
Dipper, the two separated by only 10 minutes of arc (the Dipper's
pair by 11.8 minutes). The brighter, 37 Tau (the number from the Flamsteed list), is a fourth
magnitude (4.36) common class K (K0) helium fusing giant. Its significance is more
that it leads the eye to the fainter, sixth magnitude (5.90) 39 Tau,
which is the kind of star that fascinates, a near solar class G (G5)
dwarf. Other than that, the
two have nothing to do with each other, 37 Tau 187 light years away
(give or take 3), 39 at a distance of 55.2 light years (plus or minus
0.3).
With a temperature of 4760 Kelvin, from which we can gauge the amount
of infrared radiation, 37 Tauri shines with a total radiance of 70 times
that of the Sun, from which we find a radius
of 12.3 solar and a mass of about 2.5 Suns. A direct measure of angular
diameter gives a radius of 10.5 times solar, showing that something
is as bit off. With a current age of nearly 600 million years, the
star quit hydrogen fusion some 70 million years ago. After getting
rid of its outer layers following the cessation of helium fusion, it
will turn into a white
dwarf of about 0.67 solar masses. Hovering 134 and 236 seconds
of arc away are tenth and thirteenth magnitude "companions," 37 Tau B and C, which
from their motions are just line of sight coincidences.
The fainter, 39 Tau, is not far from being another Sun, though no planets have ever been detected. Even though of a
cooler G5 spectral class (the Sun G2), the measured temperature of 5860
Kelvin is a bit warmer than the solar value of 5780 Kelvin, which might
have something to do with a somewhat higher metal content (up 25
percent) for 39 Tau. The star's luminosity is but 6 percent higher
than solar, the mass right on a solar mass, and the age a bit higher
at 6 billion years as opposed to the Sun's 4.6 billion. Another
analysis suggests a higher mass (1.1 Suns) and a much lower age of only
a billion years. The lower age is supported by a higher equatorial
rotation velocity of at least 5.5 kilometers per second, which gives
a rotation period of under 9 days (as opposed to the Sun's 25 days).
Two companions of 8th and 12th magnitude, 39 Tauri B and C, lie 177
and 149 seconds of arc away, but they too are just line of sight
happenstances. While 39 Tauri does not exactly light up the sky,
neither would the Sun as seen from 39 Tauri. At magnitude 6.0, our
seemingly brilliant Sun would be near lost amidst the stars of Scorpius near Delta
Sco.
Written by Jim Kaler 3/21/14. Return to STARS.