Stellar activity of planetary host star HD 189 733
Abstract
Aims: Extra-solar planet search programs require high-precision velocity measurements. They need to determine how to differentiate between radial-velocity variations due to Doppler motion and the noise induced by stellar activity.
Methods: We monitored the active K2V star HD 189 733 and its transiting planetary companion, which has a 2.2-day orbital period. We used the high-resolution spectograph SOPHIE mounted on the 1.93-m telescope at the Observatoire de Haute-Provence to obtain 55 spectra of HD 189 733 over nearly two months. We refined the HD 189 733b orbit parameters and placed limits on both the eccentricity and long-term velocity gradient. After subtracting the orbital motion of the planet, we compared the variability in spectroscopic activity indices with the evolution in the radial-velocity residuals and the shape of spectral lines.
Results: The radial velocity, the spectral-line profile, and the activity indices measured in He I (5875.62 Å), Hα (6562.81 Å), and both of the Ca II H&K lines (3968.47 Å and 3933.66 Å, respectively) exhibit a periodicity close to the stellar-rotation period and the correlations between them are consistent with a spotted stellar surface in rotation. We used these correlations to correct for the radial-velocity jitter due to stellar activity. This results in achieving high precision in measuring the orbital parameters, with a semi-amplitude K = 200.56 ± 0.88 m s-1 and a derived planet mass of MP = 1.13 ± 0.03 M_Jup.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- March 2009
- DOI:
- 10.1051/0004-6361:200810648
- arXiv:
- arXiv:0811.3923
- Bibcode:
- 2009A&A...495..959B
- Keywords:
-
- techniques: radial velocities;
- stars: planetary systems;
- stars: individual: HD 189 733;
- stars: activity;
- Astrophysics
- E-Print:
- 9 pages, 2 tables, 9 figures, accepted for publication in A&