paper

Radial velocity follow-up of GJ1132 with HARPS. A precise mass for planet 'b' and the discovery of a second planet

arXiv:1806.03870 · doi:10.1051/0004-6361/201731884

Abstract

GJ1132 is a nearby red dwarf known to host a transiting Earth-size planet. After its initial detection, we pursued an intense follow-up with the HARPS velocimeter. We now confirm the detection of GJ1132b with radial velocities only. We refined its orbital parameters and, in particular, its mass ( $m_{b} = 1.66 \pm 0.23 M_{\oplus}$ ), density ( $I ¨ _{b} = 6.3 \pm 1.3$ g.cm $^{- 3}$ ) and eccentricity ( $e_{b} < 0.22$ ; 95\%). We also detect at least one more planet in the system. GJ1132c is a super-Earth with period $P_{c} = 8.93 \pm 0.01$ days and minimum mass $m_{c} sin i_{c} = 2.64 \pm 0.44 M_{\oplus}$ . Receiving about 1.9 times more flux than Earth in our solar system, its equilibrium temperature is that of a temperate planet ( $T_{e q} = 230 - 300$ K for albedos $A = 0.75 - 0.00$ ) and places GJ1132c near the inner edge of the so-called habitable zone. Despite an a priori favourable orientation for the system, $S p i t z er$ observations reject most transit configurations, leaving a posterior probability $< 1%$ that GJ1132c transits. GJ1132(d) is a third signal with period $P_{d} = 177 \pm 5$ days attributed to either a planet candidate with minimum mass $m_{d} sin i_{d} = 8. 4_{- 2.5}^{+ 1.7} M_{\oplus}$ or stellar activity. (abridged)

accepted in Astronomy and Astrophysics