GAMMA PAV (Gamma Pavonis). Way down to the south, not far from the
South Celestial Pole, struts Pavo, the Peacock. Just 25 degrees off the
pole is fourth magnitude (4.22) Gamma Pavonis. Instead of ranking
third in brightness, as one might expect from its Greek letter, Gamma ties Lambda Pav
for fifth place, and is well outranked by quite bright second
magnitude Alpha Pav, which marks the
northern fringe of the constellation
eleven degrees northwest of Gamma. Not only is the star in the
midlands of its rather large constellation, it falls well into the
middle of the main sequence of hydrogen-fusing dwarfs, far from the spectacular
fringe of stellar properties. As a mid-class F (F6) dwarf, it's
much more in league with the class G2 Sun.
Indeed the two are not all that different, the similarity sparking
interest as we more or less look back at ourselves. The star is
not very far away, just 30.2 light years (give or take a tenth).
With a surface temperature of 6035 Kelvin, not all that much warmer
than the 5780 Kelvin Sun, most of the light comes out in the visual spectrum, the star just
45 percent more luminous than the Sun. Luminosity and temperature
then conspire to give a radius only 10 percent larger than solar.
With a projected equatorial rotation speed of 3.7 kilometers per
second, Gamma Pav makes a full turn in under 15 days, somewhat more
than half the solar period (though one study suggests more). The
theory of stellar structure and evolution then indicates a mass a
bit higher than that of the Sun, perhaps five percent, and suggest
that Gamma Pav might be somewhat more advanced in relative age.
Alas, no planets have ever been found, nor
has any debris disk that might mark their existence. With a
Galactic speed relative to the Sun of around three times the usual
value, and a metal content about 20 percent solar, Gamma Pavonis
seems to be a member of the so-called old disk of the Galaxy, which houses stars a bit
older than the dust-filled thin
disk in which stars are currently being born, the low metal content
perhaps explaining the lack of planetary companions. Nor for that
matter are there any known stellar companions, the star
perhaps just requiring a deeper look.
Written by Jim Kaler 11/01/13. Return to STARS.