Data on HR5185
(2000 Coordinates: RA= 13 47 15.7, Dec= +17 27 24)
Phased Doppler velocity measurements for HR 5185 (tau Boo, HD 120136).
The orbital period is 3.3128 days, and the amplitude is 468 m/s.
These observations span 1.3 years, or a total of 150 orbits. The
orbital distance (semi-major axis) of the planet is 0.0462 AU
(1 AU = 1 Earth-Sun distance). Thus the planet orbits only 8.3
stellar radii from the primary star. The inferred M sin i mass
of the planet is 3.87 Jupiter masses. This system is very
similar to the planets that have been found orbiting 51 Peg and
55 Cancer, though this planet is 5 to 10 times more massive than
them. Like the previous cases, the orbit is circular, and the
metallicity of the primary star is enhanced relative to the Sun.
Tau Boo was already suspected to be a spectroscopic binary
by Duquennoy and Mayor (1991) Astron.Astrophys. 248,485 .
Their 33 CORAVEL measurements of Tau Boo covered 5586 days (15.3 years).
A periodic variation of the radial velocity has now been detected with a period
of P=3.3120 +- 0.0002 days. This agrees well with our results.
Thus, Tau Boo represents the second planet (along with 51 Peg) for which
a confirmation has occurred.
The primary star in this system is spectral type F7V. The distance of
the star is 19 parsecs (Heintz 1993, AJ 105 1188). It is assumed
that the mass and the radius of this star are both 1.2 times greater
than the Sun. The primary star is photometrically stable at the
milli-mag level (Greg Henry, private communication).
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