Precise Radial Velocities of Giant Stars. II. Pollux and Its Planetary Companion

It has long been speculated that the observed periodic radial velocity pattern for the K giant Pollux might be explained in terms of an orbiting planetary companion. We have collected 80 high-resolution spectra for Pollux at Lick Observatory yielding precise radial velocities with a mean error of 3.8 m s-1, providing the most comprehensive and precise data set available for this star. Our data confirm the periodicity previously seen in the radial velocities. We derive a period of 589.7 ± 3.5 days and, assuming a primary mass of 1.86 M☉, a minimum companion mass of 2.9 ± 0.3MJup, consistent with earlier determinations. No evidence for any periodicities is visible in our analysis of the shapes of the spectral lines via the bisector method, so we conclude that evidence is accumulating and compelling for a planet around Pollux. However, some final doubt remains about this interpretation, because nonradial pulsations that might be present in giant stars could in principle also explain the observed radial velocities, while the accompanying bisector variations might be too small to be detectable with current data.

[1]  G. Walker,et al.  Yellow giants - A new class of radial velocity variable , 1989 .

[2]  W. D. Cochran,et al.  Confirmation of the planet hypothesis for the long-period radial velocity variations of β Geminorum , 2006, astro-ph/0606517.

[3]  C. Aerts,et al.  Discovery of solar-like oscillations in the red giant $\varepsilon$ Ophiuchi , 2006 .

[4]  W. Cochran,et al.  Long-Period Radial Velocity Variations in Three K Giants , 1993 .

[5]  P. C. Keenan,et al.  The Perkins catalog of revised MK types for the cooler stars , 1989 .

[6]  L. Girardi,et al.  Evolutionary tracks and isochrones for low- and intermediate-mass stars: From 0.15 to 7 , and from to 0.03 , 1999, astro-ph/9910164.

[7]  J. Drake,et al.  A fine analysis of calcium and iron lines in the spectrum of the K0 giant Pollux : accurate fundamental parameters , 1991 .

[8]  R. P. Butler,et al.  Precise radial velocities of giant stars I. Stable stars , 2006, astro-ph/0604502.

[9]  M. Giampapa,et al.  Limits on Line Bisector Variability for Stars with Extrasolar Planets , 2001 .

[10]  A. Walker,et al.  A LOW-AMPLITUDE PERIODICITY IN THE RADIAL VELOCITY AND CHROMOSPHERIC EMISSION OF BETA GEMINORUM , 1993 .

[11]  Sabine Frink,et al.  A Strategy for Identifying the Grid Stars for the Space Interferometry Mission , 2001 .

[12]  R. P. Butler,et al.  ATTAINING DOPPLER PRECISION OF 3 M S-1 , 1996 .

[13]  A. Hatzes.  SIMULATIONS OF STELLAR RADIAL VELOCITY AND SPECTRAL LINE BISECTOR VARIATIONS: I. NONRADIAL PULSATIONS , 1996 .

[14]  D. F. Gray.  ON THE CONSTANCY OF SPECTRAL-LINE BISECTORS. , 1983 .

[15]  R. P. Butler,et al.  Discovery of a Substellar Companion to the K2 III Giant ι Draconis , 2002 .

[16]  Detection of Solar-like Oscillations in the G7 Giant Star xi Hya , 2002, astro-ph/0209325.

[17]  H. C. Stempels,et al.  VALD{2: Progress of the Vienna Atomic Line Data Base ? , 1999 .