The detection of a massive planetary or low mass brown dwarf companion to the K giant star HD 13189 is based on precise differential radial velocity measurements obtained with the 2.0 m Alfred Jensch telescope at the Thueringer Landessternwarte Tautenburg (Germany) and with the 2.7 m Harlan J. Smith telescope as well as the Hobby-Eberly Telescope (HET) at McDonald Observatory. The giant status (K2 II) of the host star makes this discovery exceptional. Based on a comparison with evolutionary tracks we estimate a mass of the primary between 2 and 7 solar masses. HD 13189 may be the most massive star known to possess an extrasolar planet. This also demonstrates that planet formation can occur around massive early-type stars. The projected mass of the companion HD 13189 b ranges from m sin i = 8 to 20 Jupiter masses, depending on the true mass of the giant star.

Radial velocity data for HD 13189 (K2 II) from the 2.0 m Alfred Jensch telescope at Tautenburg observatory (TLS, blue circles), the Harlan J. Smith 2.7 m telescope (HJS, red triangles) and the Hobby-Eberly Telescope (HET, green boxes) at McDonald Observatory. The best-fit Keplerian orbital solution is plotted as a solid black line.
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The HD 13189 Doppler data phased to the orbital period of 472 days (empty circles are repeated data for the next cycle). The semi amplitude (K) of the signal is 173 m/s. Obviously, there is a large amount of residual scatter around this orbit. This scatter is probably caused by stellar oscillations, which are typical for K-type giant stars.
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Parameters of the companion and its orbit:
Period = 471.6 ± 6.0 [days]
T periastron = 2452327.9 ± 20.2 [days]
e = 0.27 ± 0.06
omega = 160.7 ± 12.0 [deg]
K = 173.3 ± 9.8 [m/s]
f(m) = (2.26 ± 0.37) x 1.E-07 [solar masses]
M sin i = 8 - 20 M [Jupiter masses] (depending on the mass of the primary)
a = 1.5 - 2.2 [AU]

Parameters of the host star:
Spectral type = K2 II
V = 7.57 [mag]
Hipparcos parallax = 0.54 ± 0.93 mas
M = 2 - 7 M [Sun]

References:
Hatzes A.P., Guenther E., Endl M., Cochran W.D., Doellinger M.P., and Bedalov A. 2005, A&A, accepted
paper (postscript file)

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