The planet search programme at the ESO CES and HARPS

Abstract

Context. In 1992 we began a precision radial velocity survey for planets around solar-like stars with the Coudé Echelle Spectrograph and the Long Camera (CES LC) at the 1.4 m telescope in La Silla (Chile) resulting in the discovery of the planet ι Hor b. We have continued the survey with the upgraded CES Very Long Camera (VLC) and the HARPS spectrographs, both at the 3.6 m telescope, until 2007. Aims. In this paper we present additional radial velocities for 31 stars of the original sample with higher precision. The observations cover a time span of up to 15 years and permit a search for Jupiter analogues. Methods. The survey was carried out with three different instruments/instrument configurations using the iodine absorption cell and the ThAr methods for wavelength calibration. We combine the data sets and perform a joint analysis for variability, trends, and periodicities. We compute Keplerian orbits for companions and detection limits in case of non-detections. Moreover, the HARPS radial velocities are analysed for correlations with activity indicators (CaII H&K and cross-correlation function shape). Results. We achieve a long-term RV precision of 15 m/s (CES+LC, 1992-1998, 9 m/s (CES+VLC, 1999, and 2.8 m/s (HARPS, 2003(HARPS, -2009, including archive data), respectively. This enables us to confirm the known planetary signals in ι Hor and HR 506 as well as the three known planets around HR 3259. A steady RV trend for Ind A can be explained by a planetary companion and calls for direct imaging campaigns. On the other hand, we find previously reported trends to be smaller for β Hyi and not present for α Men. The candidate planet Eri b was not detected despite our better precision. Also the planet announced for HR 4523 cannot be confirmed. Long-term trends in several of our stars are compatible with known stellar companions. We provide a spectroscopic orbital solution for the binary HR 2400 and refined solutions for the planets around HR 506 and ι Hor. For some other stars the variations could be attributed to stellar activity, as e.g. the magnetic cycle in the case of HR 8323. Conclusions. The occurrence of two Jupiter-mass planets in our sample is in line with the estimate of 10% for the frequency of giant planets with periods smaller than 10 yr around solar-like stars. We have not detected a Jupiter analogue, while the detections limits for circular orbits indicate at 5 AU a sensitivity for minimum mass of at least 1M Jup (2M Jup ) for 13% (61%) of the stars.

Signals embedded in the radial velocity noise

“…With a distance of only 3.7 pc, HD 10700 is the third closest star reported to be a host to a putative planetary system after Eridani (Hatzes et al 2000) with a distance of 3.2 pc and α Centauri B (Dumusque et al 2012) with a distance of 1.3 pc, though both of these remain to be confirmed and Zechmeister et al (2013) have casted considerable doubt on the existence of a planet around Eridani. This makes HD 10700 an ideal target for future direct-imaging missions.…”

ζ2Reticuli, its debris disk, and its lonely stellar companionζ1Ret

“…This could be the reason that the T c slopes for this star are less significant compared to those of its companion. The two stars exhibit different levels of activity; ζ 1 Ret ( log R HK = −4.662) is more active than ζ 2 Ret ( log R HK = −4.892) (Zechmeister et al 2013). Although ζ 1 Ret is more active than its companion, the stellar variability should not play a significant role in the observed difference in the chemical abundances between the different spectra of the star since, again, the observations are carried out on the same night.…”

Magnetic field measurements of ϵ Eridani from Zeeman broadening

“…Benedict et al (2006) and Reffert & Quirrenbach (2011) refined the orbital solution and combined the radial velocities with astrometric observations and derived a likely mass for the planet of 1.55 M Jup . However, Zechmeister et al (2013) could not confirm the existence of this planet from higherprecision radial-velocity data nor did Anglada- Escudé & Butler (2012) succeed to coherently combine the different radial velocity data sets with the original 2500-d period.…”