The CORALIE survey for southern extra-solar planets VII. Two short-period Saturnian companions to HD108147 and HD168746

TL;DR

This paper reports the discovery of two Saturn-mass exoplanets with short orbital periods around stars HD108147 and HD168746, using high-precision Doppler measurements from the CORALIE spectrograph, and introduces improved data analysis techniques.

Contribution

It presents the discovery of two new Saturn-mass exoplanets and introduces enhanced radial velocity measurement methods for detecting such planets.

Findings

Discovered two Saturn-mass planets with short periods.

Achieved radial velocity precision better than 3 m/s.

Improved data analysis techniques for telluric line mitigation.

Abstract

We present the discovery of two Saturn-mass companions to HD108147 and HD168746. Both belong to the lightest ever discovered planets. The minimum mass of the companion to HD168746 is of only 0.77 the mass of Saturn and its orbital period is 6.4 days. The companion to HD108147 orbits its parent star in 10.9 days and its minimum mass is 1.34 that of Saturn. Its orbit is characterized by a high eccentricity, e=0.50, indicating possibly the presence of a second companion. The detection of Saturn-mass planets by means of the Doppler technique demands high radial-velocity measurement precision. The two new candidates were discovered by means of the CORALIE echelle spectrograph. The instrumental accuracy of CORALIE combined with the simultaneous ThAr-reference technique has reached a level better than 3m/s. On many observed objects the precision is now limited by photon noise. We present in this paper the weighted cross-correlation technique, which leads to an improvement in the photon noise of the computed radial velocity. We discuss as well a modification of the numerical cross-correlation mask which reduces significantly the residual perturbation effects produced by telluric absorption lines.